// SPDX-License-Identifier: GPL-2.0
/*
 * trace_events_hist - trace event hist triggers
 *
 * Copyright (C) 2015 Tom Zanussi <tom.zanussi@linux.intel.com>
 */

#include <linux/module.h>
#include <linux/kallsyms.h>
#include <linux/security.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/stacktrace.h>
#include <linux/rculist.h>
#include <linux/tracefs.h>

/* for gfp flag names */
#include <linux/trace_events.h>
#include <trace/events/mmflags.h>

#include "tracing_map.h"
#include "trace_synth.h"

#define ERRORS                                                          \
        C(NONE,                 "No error"),                            \
        C(DUPLICATE_VAR,        "Variable already defined"),            \
        C(VAR_NOT_UNIQUE,       "Variable name not unique, need to use fully qualified name (subsys.event.var) for variable"), \
        C(TOO_MANY_VARS,        "Too many variables defined"),          \
        C(MALFORMED_ASSIGNMENT, "Malformed assignment"),                \
        C(NAMED_MISMATCH,       "Named hist trigger doesn't match existing named trigger (includes variables)"), \
        C(TRIGGER_EEXIST,       "Hist trigger already exists"),         \
        C(TRIGGER_ENOENT_CLEAR, "Can't clear or continue a nonexistent hist trigger"), \
        C(SET_CLOCK_FAIL,       "Couldn't set trace_clock"),            \
        C(BAD_FIELD_MODIFIER,   "Invalid field modifier"),              \
        C(TOO_MANY_SUBEXPR,     "Too many subexpressions (3 max)"),     \
        C(TIMESTAMP_MISMATCH,   "Timestamp units in expression don't match"), \
        C(TOO_MANY_FIELD_VARS,  "Too many field variables defined"),    \
        C(EVENT_FILE_NOT_FOUND, "Event file not found"),                \
        C(HIST_NOT_FOUND,       "Matching event histogram not found"),  \
        C(HIST_CREATE_FAIL,     "Couldn't create histogram for field"), \
        C(SYNTH_VAR_NOT_FOUND,  "Couldn't find synthetic variable"),    \
        C(SYNTH_EVENT_NOT_FOUND,"Couldn't find synthetic event"),       \
        C(SYNTH_TYPE_MISMATCH,  "Param type doesn't match synthetic event field type"), \
        C(SYNTH_COUNT_MISMATCH, "Param count doesn't match synthetic event field count"), \
        C(FIELD_VAR_PARSE_FAIL, "Couldn't parse field variable"),       \
        C(VAR_CREATE_FIND_FAIL, "Couldn't create or find variable"),    \
        C(ONX_NOT_VAR,          "For onmax(x) or onchange(x), x must be a variable"), \
        C(ONX_VAR_NOT_FOUND,    "Couldn't find onmax or onchange variable"), \
        C(ONX_VAR_CREATE_FAIL,  "Couldn't create onmax or onchange variable"), \
        C(FIELD_VAR_CREATE_FAIL,"Couldn't create field variable"),      \
        C(TOO_MANY_PARAMS,      "Too many action params"),              \
        C(PARAM_NOT_FOUND,      "Couldn't find param"),                 \
        C(INVALID_PARAM,        "Invalid action param"),                \
        C(ACTION_NOT_FOUND,     "No action found"),                     \
        C(NO_SAVE_PARAMS,       "No params found for save()"),          \
        C(TOO_MANY_SAVE_ACTIONS,"Can't have more than one save() action per hist"), \
        C(ACTION_MISMATCH,      "Handler doesn't support action"),      \
        C(NO_CLOSING_PAREN,     "No closing paren found"),              \
        C(SUBSYS_NOT_FOUND,     "Missing subsystem"),                   \
        C(INVALID_SUBSYS_EVENT, "Invalid subsystem or event name"),     \
        C(INVALID_REF_KEY,      "Using variable references in keys not supported"), \
        C(VAR_NOT_FOUND,        "Couldn't find variable"),              \
        C(FIELD_NOT_FOUND,      "Couldn't find field"),                 \
        C(EMPTY_ASSIGNMENT,     "Empty assignment"),                    \
        C(INVALID_SORT_MODIFIER,"Invalid sort modifier"),               \
        C(EMPTY_SORT_FIELD,     "Empty sort field"),                    \
        C(TOO_MANY_SORT_FIELDS, "Too many sort fields (Max = 2)"),      \
        C(INVALID_SORT_FIELD,   "Sort field must be a key or a val"),

#undef C
#define C(a, b)         HIST_ERR_##a

enum { ERRORS };

#undef C
#define C(a, b)         b

static const char *err_text[] = { ERRORS };

struct hist_field;

typedef u64 (*hist_field_fn_t) (struct hist_field *field,
                                struct tracing_map_elt *elt,
                                struct ring_buffer_event *rbe,
                                void *event);

#define HIST_FIELD_OPERANDS_MAX 2
#define HIST_FIELDS_MAX         (TRACING_MAP_FIELDS_MAX + TRACING_MAP_VARS_MAX)
#define HIST_ACTIONS_MAX        8

enum field_op_id {
        FIELD_OP_NONE,
        FIELD_OP_PLUS,
        FIELD_OP_MINUS,
        FIELD_OP_UNARY_MINUS,
};

/*
 * A hist_var (histogram variable) contains variable information for
 * hist_fields having the HIST_FIELD_FL_VAR or HIST_FIELD_FL_VAR_REF
 * flag set.  A hist_var has a variable name e.g. ts0, and is
 * associated with a given histogram trigger, as specified by
 * hist_data.  The hist_var idx is the unique index assigned to the
 * variable by the hist trigger's tracing_map.  The idx is what is
 * used to set a variable's value and, by a variable reference, to
 * retrieve it.
 */
struct hist_var {
        char                            *name;
        struct hist_trigger_data        *hist_data;
        unsigned int                    idx;
};

struct hist_field {
        struct ftrace_event_field       *field;
        unsigned long                   flags;
        hist_field_fn_t                 fn;
        unsigned int                    ref;
        unsigned int                    size;
        unsigned int                    offset;
        unsigned int                    is_signed;
        const char                      *type;
        struct hist_field               *operands[HIST_FIELD_OPERANDS_MAX];
        struct hist_trigger_data        *hist_data;

        /*
         * Variable fields contain variable-specific info in var.
         */
        struct hist_var                 var;
        enum field_op_id                operator;
        char                            *system;
        char                            *event_name;

        /*
         * The name field is used for EXPR and VAR_REF fields.  VAR
         * fields contain the variable name in var.name.
         */
        char                            *name;

        /*
         * When a histogram trigger is hit, if it has any references
         * to variables, the values of those variables are collected
         * into a var_ref_vals array by resolve_var_refs().  The
         * current value of each variable is read from the tracing_map
         * using the hist field's hist_var.idx and entered into the
         * var_ref_idx entry i.e. var_ref_vals[var_ref_idx].
         */
        unsigned int                    var_ref_idx;
        bool                            read_once;

        unsigned int                    var_str_idx;
};

static u64 hist_field_none(struct hist_field *field,
                           struct tracing_map_elt *elt,
                           struct ring_buffer_event *rbe,
                           void *event)
{
        return 0;
}

static u64 hist_field_counter(struct hist_field *field,
                              struct tracing_map_elt *elt,
                              struct ring_buffer_event *rbe,
                              void *event)
{
        return 1;
}

static u64 hist_field_string(struct hist_field *hist_field,
                             struct tracing_map_elt *elt,
                             struct ring_buffer_event *rbe,
                             void *event)
{
        char *addr = (char *)(event + hist_field->field->offset);

        return (u64)(unsigned long)addr;
}

static u64 hist_field_dynstring(struct hist_field *hist_field,
                                struct tracing_map_elt *elt,
                                struct ring_buffer_event *rbe,
                                void *event)
{
        u32 str_item = *(u32 *)(event + hist_field->field->offset);
        int str_loc = str_item & 0xffff;
        char *addr = (char *)(event + str_loc);

        return (u64)(unsigned long)addr;
}

static u64 hist_field_pstring(struct hist_field *hist_field,
                              struct tracing_map_elt *elt,
                              struct ring_buffer_event *rbe,
                              void *event)
{
        char **addr = (char **)(event + hist_field->field->offset);

        return (u64)(unsigned long)*addr;
}

static u64 hist_field_log2(struct hist_field *hist_field,
                           struct tracing_map_elt *elt,
                           struct ring_buffer_event *rbe,
                           void *event)
{
        struct hist_field *operand = hist_field->operands[0];

        u64 val = operand->fn(operand, elt, rbe, event);

        return (u64) ilog2(roundup_pow_of_two(val));
}

static u64 hist_field_plus(struct hist_field *hist_field,
                           struct tracing_map_elt *elt,
                           struct ring_buffer_event *rbe,
                           void *event)
{
        struct hist_field *operand1 = hist_field->operands[0];
        struct hist_field *operand2 = hist_field->operands[1];

        u64 val1 = operand1->fn(operand1, elt, rbe, event);
        u64 val2 = operand2->fn(operand2, elt, rbe, event);

        return val1 + val2;
}

static u64 hist_field_minus(struct hist_field *hist_field,
                            struct tracing_map_elt *elt,
                            struct ring_buffer_event *rbe,
                            void *event)
{
        struct hist_field *operand1 = hist_field->operands[0];
        struct hist_field *operand2 = hist_field->operands[1];

        u64 val1 = operand1->fn(operand1, elt, rbe, event);
        u64 val2 = operand2->fn(operand2, elt, rbe, event);

        return val1 - val2;
}

static u64 hist_field_unary_minus(struct hist_field *hist_field,
                                  struct tracing_map_elt *elt,
                                  struct ring_buffer_event *rbe,
                                  void *event)
{
        struct hist_field *operand = hist_field->operands[0];

        s64 sval = (s64)operand->fn(operand, elt, rbe, event);
        u64 val = (u64)-sval;

        return val;
}

#define DEFINE_HIST_FIELD_FN(type)                                      \
        static u64 hist_field_##type(struct hist_field *hist_field,     \
                                     struct tracing_map_elt *elt,       \
                                     struct ring_buffer_event *rbe,     \
                                     void *event)                       \
{                                                                       \
        type *addr = (type *)(event + hist_field->field->offset);       \
                                                                        \
        return (u64)(unsigned long)*addr;                               \
}

DEFINE_HIST_FIELD_FN(s64);
DEFINE_HIST_FIELD_FN(u64);
DEFINE_HIST_FIELD_FN(s32);
DEFINE_HIST_FIELD_FN(u32);
DEFINE_HIST_FIELD_FN(s16);
DEFINE_HIST_FIELD_FN(u16);
DEFINE_HIST_FIELD_FN(s8);
DEFINE_HIST_FIELD_FN(u8);

#define for_each_hist_field(i, hist_data)       \
        for ((i) = 0; (i) < (hist_data)->n_fields; (i)++)

#define for_each_hist_val_field(i, hist_data)   \
        for ((i) = 0; (i) < (hist_data)->n_vals; (i)++)

#define for_each_hist_key_field(i, hist_data)   \
        for ((i) = (hist_data)->n_vals; (i) < (hist_data)->n_fields; (i)++)

#define HIST_STACKTRACE_DEPTH   16
#define HIST_STACKTRACE_SIZE    (HIST_STACKTRACE_DEPTH * sizeof(unsigned long))
#define HIST_STACKTRACE_SKIP    5

#define HITCOUNT_IDX            0
#define HIST_KEY_SIZE_MAX       (MAX_FILTER_STR_VAL + HIST_STACKTRACE_SIZE)

enum hist_field_flags {
        HIST_FIELD_FL_HITCOUNT          = 1 << 0,
        HIST_FIELD_FL_KEY               = 1 << 1,
        HIST_FIELD_FL_STRING            = 1 << 2,
        HIST_FIELD_FL_HEX               = 1 << 3,
        HIST_FIELD_FL_SYM               = 1 << 4,
        HIST_FIELD_FL_SYM_OFFSET        = 1 << 5,
        HIST_FIELD_FL_EXECNAME          = 1 << 6,
        HIST_FIELD_FL_SYSCALL           = 1 << 7,
        HIST_FIELD_FL_STACKTRACE        = 1 << 8,
        HIST_FIELD_FL_LOG2              = 1 << 9,
        HIST_FIELD_FL_TIMESTAMP         = 1 << 10,
        HIST_FIELD_FL_TIMESTAMP_USECS   = 1 << 11,
        HIST_FIELD_FL_VAR               = 1 << 12,
        HIST_FIELD_FL_EXPR              = 1 << 13,
        HIST_FIELD_FL_VAR_REF           = 1 << 14,
        HIST_FIELD_FL_CPU               = 1 << 15,
        HIST_FIELD_FL_ALIAS             = 1 << 16,
};

struct var_defs {
        unsigned int    n_vars;
        char            *name[TRACING_MAP_VARS_MAX];
        char            *expr[TRACING_MAP_VARS_MAX];
};

struct hist_trigger_attrs {
        char            *keys_str;
        char            *vals_str;
        char            *sort_key_str;
        char            *name;
        char            *clock;
        bool            pause;
        bool            cont;
        bool            clear;
        bool            ts_in_usecs;
        unsigned int    map_bits;

        char            *assignment_str[TRACING_MAP_VARS_MAX];
        unsigned int    n_assignments;

        char            *action_str[HIST_ACTIONS_MAX];
        unsigned int    n_actions;

        struct var_defs var_defs;
};

struct field_var {
        struct hist_field       *var;
        struct hist_field       *val;
};

struct field_var_hist {
        struct hist_trigger_data        *hist_data;
        char                            *cmd;
};

struct hist_trigger_data {
        struct hist_field               *fields[HIST_FIELDS_MAX];
        unsigned int                    n_vals;
        unsigned int                    n_keys;
        unsigned int                    n_fields;
        unsigned int                    n_vars;
        unsigned int                    n_var_str;
        unsigned int                    key_size;
        struct tracing_map_sort_key     sort_keys[TRACING_MAP_SORT_KEYS_MAX];
        unsigned int                    n_sort_keys;
        struct trace_event_file         *event_file;
        struct hist_trigger_attrs       *attrs;
        struct tracing_map              *map;
        bool                            enable_timestamps;
        bool                            remove;
        struct hist_field               *var_refs[TRACING_MAP_VARS_MAX];
        unsigned int                    n_var_refs;

        struct action_data              *actions[HIST_ACTIONS_MAX];
        unsigned int                    n_actions;

        struct field_var                *field_vars[SYNTH_FIELDS_MAX];
        unsigned int                    n_field_vars;
        unsigned int                    n_field_var_str;
        struct field_var_hist           *field_var_hists[SYNTH_FIELDS_MAX];
        unsigned int                    n_field_var_hists;

        struct field_var                *save_vars[SYNTH_FIELDS_MAX];
        unsigned int                    n_save_vars;
        unsigned int                    n_save_var_str;
};

struct action_data;

typedef void (*action_fn_t) (struct hist_trigger_data *hist_data,
                             struct tracing_map_elt *elt, void *rec,
                             struct ring_buffer_event *rbe, void *key,
                             struct action_data *data, u64 *var_ref_vals);

typedef bool (*check_track_val_fn_t) (u64 track_val, u64 var_val);

enum handler_id {
        HANDLER_ONMATCH = 1,
        HANDLER_ONMAX,
        HANDLER_ONCHANGE,
};

enum action_id {
        ACTION_SAVE = 1,
        ACTION_TRACE,
        ACTION_SNAPSHOT,
};

struct action_data {
        enum handler_id         handler;
        enum action_id          action;
        char                    *action_name;
        action_fn_t             fn;

        unsigned int            n_params;
        char                    *params[SYNTH_FIELDS_MAX];

        /*
         * When a histogram trigger is hit, the values of any
         * references to variables, including variables being passed
         * as parameters to synthetic events, are collected into a
         * var_ref_vals array.  This var_ref_idx array is an array of
         * indices into the var_ref_vals array, one for each synthetic
         * event param, and is passed to the synthetic event
         * invocation.
         */
        unsigned int            var_ref_idx[TRACING_MAP_VARS_MAX];
        struct synth_event      *synth_event;
        bool                    use_trace_keyword;
        char                    *synth_event_name;

        union {
                struct {
                        char                    *event;
                        char                    *event_system;
                } match_data;

                struct {
                        /*
                         * var_str contains the $-unstripped variable
                         * name referenced by var_ref, and used when
                         * printing the action.  Because var_ref
                         * creation is deferred to create_actions(),
                         * we need a per-action way to save it until
                         * then, thus var_str.
                         */
                        char                    *var_str;

                        /*
                         * var_ref refers to the variable being
                         * tracked e.g onmax($var).
                         */
                        struct hist_field       *var_ref;

                        /*
                         * track_var contains the 'invisible' tracking
                         * variable created to keep the current
                         * e.g. max value.
                         */
                        struct hist_field       *track_var;

                        check_track_val_fn_t    check_val;
                        action_fn_t             save_data;
                } track_data;
        };
};

struct track_data {
        u64                             track_val;
        bool                            updated;

        unsigned int                    key_len;
        void                            *key;
        struct tracing_map_elt          elt;

        struct action_data              *action_data;
        struct hist_trigger_data        *hist_data;
};

struct hist_elt_data {
        char *comm;
        u64 *var_ref_vals;
        char *field_var_str[SYNTH_FIELDS_MAX];
};

struct snapshot_context {
        struct tracing_map_elt  *elt;
        void                    *key;
};

static void track_data_free(struct track_data *track_data)
{
        struct hist_elt_data *elt_data;

        if (!track_data)
                return;

        kfree(track_data->key);

        elt_data = track_data->elt.private_data;
        if (elt_data) {
                kfree(elt_data->comm);
                kfree(elt_data);
        }

        kfree(track_data);
}

static struct track_data *track_data_alloc(unsigned int key_len,
                                           struct action_data *action_data,
                                           struct hist_trigger_data *hist_data)
{
        struct track_data *data = kzalloc(sizeof(*data), GFP_KERNEL);
        struct hist_elt_data *elt_data;

        if (!data)
                return ERR_PTR(-ENOMEM);

        data->key = kzalloc(key_len, GFP_KERNEL);
        if (!data->key) {
                track_data_free(data);
                return ERR_PTR(-ENOMEM);
        }

        data->key_len = key_len;
        data->action_data = action_data;
        data->hist_data = hist_data;

        elt_data = kzalloc(sizeof(*elt_data), GFP_KERNEL);
        if (!elt_data) {
                track_data_free(data);
                return ERR_PTR(-ENOMEM);
        }

        data->elt.private_data = elt_data;

        elt_data->comm = kzalloc(TASK_COMM_LEN, GFP_KERNEL);
        if (!elt_data->comm) {
                track_data_free(data);
                return ERR_PTR(-ENOMEM);
        }

        return data;
}

static char last_cmd[MAX_FILTER_STR_VAL];
static char last_cmd_loc[MAX_FILTER_STR_VAL];

static int errpos(char *str)
{
        return err_pos(last_cmd, str);
}

static void last_cmd_set(struct trace_event_file *file, char *str)
{
        const char *system = NULL, *name = NULL;
        struct trace_event_call *call;

        if (!str)
                return;

        strcpy(last_cmd, "hist:");
        strncat(last_cmd, str, MAX_FILTER_STR_VAL - 1 - sizeof("hist:"));

        if (file) {
                call = file->event_call;
                system = call->class->system;
                if (system) {
                        name = trace_event_name(call);
                        if (!name)
                                system = NULL;
                }
        }

        if (system)
                snprintf(last_cmd_loc, MAX_FILTER_STR_VAL, "hist:%s:%s", system, name);
}

static void hist_err(struct trace_array *tr, u8 err_type, u8 err_pos)
{
        tracing_log_err(tr, last_cmd_loc, last_cmd, err_text,
                        err_type, err_pos);
}

static void hist_err_clear(void)
{
        last_cmd[0] = '\0';
        last_cmd_loc[0] = '\0';
}

typedef void (*synth_probe_func_t) (void *__data, u64 *var_ref_vals,
                                    unsigned int *var_ref_idx);

static inline void trace_synth(struct synth_event *event, u64 *var_ref_vals,
                               unsigned int *var_ref_idx)
{
        struct tracepoint *tp = event->tp;

        if (unlikely(atomic_read(&tp->key.enabled) > 0)) {
                struct tracepoint_func *probe_func_ptr;
                synth_probe_func_t probe_func;
                void *__data;

                if (!(cpu_online(raw_smp_processor_id())))
                        return;

                probe_func_ptr = rcu_dereference_sched((tp)->funcs);
                if (probe_func_ptr) {
                        do {
                                probe_func = probe_func_ptr->func;
                                __data = probe_func_ptr->data;
                                probe_func(__data, var_ref_vals, var_ref_idx);
                        } while ((++probe_func_ptr)->func);
                }
        }
}

static void action_trace(struct hist_trigger_data *hist_data,
                         struct tracing_map_elt *elt, void *rec,
                         struct ring_buffer_event *rbe, void *key,
                         struct action_data *data, u64 *var_ref_vals)
{
        struct synth_event *event = data->synth_event;

        trace_synth(event, var_ref_vals, data->var_ref_idx);
}

struct hist_var_data {
        struct list_head list;
        struct hist_trigger_data *hist_data;
};

static u64 hist_field_timestamp(struct hist_field *hist_field,
                                struct tracing_map_elt *elt,
                                struct ring_buffer_event *rbe,
                                void *event)
{
        struct hist_trigger_data *hist_data = hist_field->hist_data;
        struct trace_array *tr = hist_data->event_file->tr;

        u64 ts = ring_buffer_event_time_stamp(rbe);

        if (hist_data->attrs->ts_in_usecs && trace_clock_in_ns(tr))
                ts = ns2usecs(ts);

        return ts;
}

static u64 hist_field_cpu(struct hist_field *hist_field,
                          struct tracing_map_elt *elt,
                          struct ring_buffer_event *rbe,
                          void *event)
{
        int cpu = smp_processor_id();

        return cpu;
}

/**
 * check_field_for_var_ref - Check if a VAR_REF field references a variable
 * @hist_field: The VAR_REF field to check
 * @var_data: The hist trigger that owns the variable
 * @var_idx: The trigger variable identifier
 *
 * Check the given VAR_REF field to see whether or not it references
 * the given variable associated with the given trigger.
 *
 * Return: The VAR_REF field if it does reference the variable, NULL if not
 */
static struct hist_field *
check_field_for_var_ref(struct hist_field *hist_field,
                        struct hist_trigger_data *var_data,
                        unsigned int var_idx)
{
        WARN_ON(!(hist_field && hist_field->flags & HIST_FIELD_FL_VAR_REF));

        if (hist_field && hist_field->var.idx == var_idx &&
            hist_field->var.hist_data == var_data)
                return hist_field;

        return NULL;
}

/**
 * find_var_ref - Check if a trigger has a reference to a trigger variable
 * @hist_data: The hist trigger that might have a reference to the variable
 * @var_data: The hist trigger that owns the variable
 * @var_idx: The trigger variable identifier
 *
 * Check the list of var_refs[] on the first hist trigger to see
 * whether any of them are references to the variable on the second
 * trigger.
 *
 * Return: The VAR_REF field referencing the variable if so, NULL if not
 */
static struct hist_field *find_var_ref(struct hist_trigger_data *hist_data,
                                       struct hist_trigger_data *var_data,
                                       unsigned int var_idx)
{
        struct hist_field *hist_field;
        unsigned int i;

        for (i = 0; i < hist_data->n_var_refs; i++) {
                hist_field = hist_data->var_refs[i];
                if (check_field_for_var_ref(hist_field, var_data, var_idx))
                        return hist_field;
        }

        return NULL;
}

/**
 * find_any_var_ref - Check if there is a reference to a given trigger variable
 * @hist_data: The hist trigger
 * @var_idx: The trigger variable identifier
 *
 * Check to see whether the given variable is currently referenced by
 * any other trigger.
 *
 * The trigger the variable is defined on is explicitly excluded - the
 * assumption being that a self-reference doesn't prevent a trigger
 * from being removed.
 *
 * Return: The VAR_REF field referencing the variable if so, NULL if not
 */
static struct hist_field *find_any_var_ref(struct hist_trigger_data *hist_data,
                                           unsigned int var_idx)
{
        struct trace_array *tr = hist_data->event_file->tr;
        struct hist_field *found = NULL;
        struct hist_var_data *var_data;

        list_for_each_entry(var_data, &tr->hist_vars, list) {
                if (var_data->hist_data == hist_data)
                        continue;
                found = find_var_ref(var_data->hist_data, hist_data, var_idx);
                if (found)
                        break;
        }

        return found;
}

/**
 * check_var_refs - Check if there is a reference to any of trigger's variables
 * @hist_data: The hist trigger
 *
 * A trigger can define one or more variables.  If any one of them is
 * currently referenced by any other trigger, this function will
 * determine that.

 * Typically used to determine whether or not a trigger can be removed
 * - if there are any references to a trigger's variables, it cannot.
 *
 * Return: True if there is a reference to any of trigger's variables
 */
static bool check_var_refs(struct hist_trigger_data *hist_data)
{
        struct hist_field *field;
        bool found = false;
        int i;

        for_each_hist_field(i, hist_data) {
                field = hist_data->fields[i];
                if (field && field->flags & HIST_FIELD_FL_VAR) {
                        if (find_any_var_ref(hist_data, field->var.idx)) {
                                found = true;
                                break;
                        }
                }
        }

        return found;
}

static struct hist_var_data *find_hist_vars(struct hist_trigger_data *hist_data)
{
        struct trace_array *tr = hist_data->event_file->tr;
        struct hist_var_data *var_data, *found = NULL;

        list_for_each_entry(var_data, &tr->hist_vars, list) {
                if (var_data->hist_data == hist_data) {
                        found = var_data;
                        break;
                }
        }

        return found;
}

static bool field_has_hist_vars(struct hist_field *hist_field,
                                unsigned int level)
{
        int i;

        if (level > 3)
                return false;

        if (!hist_field)
                return false;

        if (hist_field->flags & HIST_FIELD_FL_VAR ||
            hist_field->flags & HIST_FIELD_FL_VAR_REF)
                return true;

        for (i = 0; i < HIST_FIELD_OPERANDS_MAX; i++) {
                struct hist_field *operand;

                operand = hist_field->operands[i];
                if (field_has_hist_vars(operand, level + 1))
                        return true;
        }

        return false;
}

static bool has_hist_vars(struct hist_trigger_data *hist_data)
{
        struct hist_field *hist_field;
        int i;

        for_each_hist_field(i, hist_data) {
                hist_field = hist_data->fields[i];
                if (field_has_hist_vars(hist_field, 0))
                        return true;
        }

        return false;
}

static int save_hist_vars(struct hist_trigger_data *hist_data)
{
        struct trace_array *tr = hist_data->event_file->tr;
        struct hist_var_data *var_data;

        var_data = find_hist_vars(hist_data);
        if (var_data)
                return 0;

        if (tracing_check_open_get_tr(tr))
                return -ENODEV;

        var_data = kzalloc(sizeof(*var_data), GFP_KERNEL);
        if (!var_data) {
                trace_array_put(tr);
                return -ENOMEM;
        }

        var_data->hist_data = hist_data;
        list_add(&var_data->list, &tr->hist_vars);

        return 0;
}

static void remove_hist_vars(struct hist_trigger_data *hist_data)
{
        struct trace_array *tr = hist_data->event_file->tr;
        struct hist_var_data *var_data;

        var_data = find_hist_vars(hist_data);
        if (!var_data)
                return;

        if (WARN_ON(check_var_refs(hist_data)))
                return;

        list_del(&var_data->list);

        kfree(var_data);

        trace_array_put(tr);
}

static struct hist_field *find_var_field(struct hist_trigger_data *hist_data,
                                         const char *var_name)
{
        struct hist_field *hist_field, *found = NULL;
        int i;

        for_each_hist_field(i, hist_data) {
                hist_field = hist_data->fields[i];
                if (hist_field && hist_field->flags & HIST_FIELD_FL_VAR &&
                    strcmp(hist_field->var.name, var_name) == 0) {
                        found = hist_field;
                        break;
                }
        }

        return found;
}

static struct hist_field *find_var(struct hist_trigger_data *hist_data,
                                   struct trace_event_file *file,
                                   const char *var_name)
{
        struct hist_trigger_data *test_data;
        struct event_trigger_data *test;
        struct hist_field *hist_field;

        lockdep_assert_held(&event_mutex);

        hist_field = find_var_field(hist_data, var_name);
        if (hist_field)
                return hist_field;

        list_for_each_entry(test, &file->triggers, list) {
                if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
                        test_data = test->private_data;
                        hist_field = find_var_field(test_data, var_name);
                        if (hist_field)
                                return hist_field;
                }
        }

        return NULL;
}

static struct trace_event_file *find_var_file(struct trace_array *tr,
                                              char *system,
                                              char *event_name,
                                              char *var_name)
{
        struct hist_trigger_data *var_hist_data;
        struct hist_var_data *var_data;
        struct trace_event_file *file, *found = NULL;

        if (system)
                return find_event_file(tr, system, event_name);

        list_for_each_entry(var_data, &tr->hist_vars, list) {
                var_hist_data = var_data->hist_data;
                file = var_hist_data->event_file;
                if (file == found)
                        continue;

                if (find_var_field(var_hist_data, var_name)) {
                        if (found) {
                                hist_err(tr, HIST_ERR_VAR_NOT_UNIQUE, errpos(var_name));
                                return NULL;
                        }

                        found = file;
                }
        }

        return found;
}

static struct hist_field *find_file_var(struct trace_event_file *file,
                                        const char *var_name)
{
        struct hist_trigger_data *test_data;
        struct event_trigger_data *test;
        struct hist_field *hist_field;

        lockdep_assert_held(&event_mutex);

        list_for_each_entry(test, &file->triggers, list) {
                if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
                        test_data = test->private_data;
                        hist_field = find_var_field(test_data, var_name);
                        if (hist_field)
                                return hist_field;
                }
        }

        return NULL;
}

static struct hist_field *
find_match_var(struct hist_trigger_data *hist_data, char *var_name)
{
        struct trace_array *tr = hist_data->event_file->tr;
        struct hist_field *hist_field, *found = NULL;
        struct trace_event_file *file;
        unsigned int i;

        for (i = 0; i < hist_data->n_actions; i++) {
                struct action_data *data = hist_data->actions[i];

                if (data->handler == HANDLER_ONMATCH) {
                        char *system = data->match_data.event_system;
                        char *event_name = data->match_data.event;

                        file = find_var_file(tr, system, event_name, var_name);
                        if (!file)
                                continue;
                        hist_field = find_file_var(file, var_name);
                        if (hist_field) {
                                if (found) {
                                        hist_err(tr, HIST_ERR_VAR_NOT_UNIQUE,
                                                 errpos(var_name));
                                        return ERR_PTR(-EINVAL);
                                }

                                found = hist_field;
                        }
                }
        }
        return found;
}

static struct hist_field *find_event_var(struct hist_trigger_data *hist_data,
                                         char *system,
                                         char *event_name,
                                         char *var_name)
{
        struct trace_array *tr = hist_data->event_file->tr;

        struct hist_field *hist_field = NULL;
        struct trace_event_file *file;

        if (!system || !event_name) {
                hist_field = find_match_var(hist_data, var_name);
                if (IS_ERR(hist_field))
                        return NULL;
                if (hist_field)
                        return hist_field;
        }

        file = find_var_file(tr, system, event_name, var_name);
        if (!file)
                return NULL;

        hist_field = find_file_var(file, var_name);

        return hist_field;
}

static u64 hist_field_var_ref(struct hist_field *hist_field,
                              struct tracing_map_elt *elt,
                              struct ring_buffer_event *rbe,
                              void *event)
{
        struct hist_elt_data *elt_data;
        u64 var_val = 0;

        if (WARN_ON_ONCE(!elt))
                return var_val;

        elt_data = elt->private_data;
        var_val = elt_data->var_ref_vals[hist_field->var_ref_idx];

        return var_val;
}

static bool resolve_var_refs(struct hist_trigger_data *hist_data, void *key,
                             u64 *var_ref_vals, bool self)
{
        struct hist_trigger_data *var_data;
        struct tracing_map_elt *var_elt;
        struct hist_field *hist_field;
        unsigned int i, var_idx;
        bool resolved = true;
        u64 var_val = 0;

        for (i = 0; i < hist_data->n_var_refs; i++) {
                hist_field = hist_data->var_refs[i];
                var_idx = hist_field->var.idx;
                var_data = hist_field->var.hist_data;

                if (var_data == NULL) {
                        resolved = false;
                        break;
                }

                if ((self && var_data != hist_data) ||
                    (!self && var_data == hist_data))
                        continue;

                var_elt = tracing_map_lookup(var_data->map, key);
                if (!var_elt) {
                        resolved = false;
                        break;
                }

                if (!tracing_map_var_set(var_elt, var_idx)) {
                        resolved = false;
                        break;
                }

                if (self || !hist_field->read_once)
                        var_val = tracing_map_read_var(var_elt, var_idx);
                else
                        var_val = tracing_map_read_var_once(var_elt, var_idx);

                var_ref_vals[i] = var_val;
        }

        return resolved;
}

static const char *hist_field_name(struct hist_field *field,
                                   unsigned int level)
{
        const char *field_name = "";

        if (level > 1)
                return field_name;

        if (field->field)
                field_name = field->field->name;
        else if (field->flags & HIST_FIELD_FL_LOG2 ||
                 field->flags & HIST_FIELD_FL_ALIAS)
                field_name = hist_field_name(field->operands[0], ++level);
        else if (field->flags & HIST_FIELD_FL_CPU)
                field_name = "cpu";
        else if (field->flags & HIST_FIELD_FL_EXPR ||
                 field->flags & HIST_FIELD_FL_VAR_REF) {
                if (field->system) {
                        static char full_name[MAX_FILTER_STR_VAL];

                        strcat(full_name, field->system);
                        strcat(full_name, ".");
                        strcat(full_name, field->event_name);
                        strcat(full_name, ".");
                        strcat(full_name, field->name);
                        field_name = full_name;
                } else
                        field_name = field->name;
        } else if (field->flags & HIST_FIELD_FL_TIMESTAMP)
                field_name = "common_timestamp";

        if (field_name == NULL)
                field_name = "";

        return field_name;
}

static hist_field_fn_t select_value_fn(int field_size, int field_is_signed)
{
        hist_field_fn_t fn = NULL;

        switch (field_size) {
        case 8:
                if (field_is_signed)
                        fn = hist_field_s64;
                else
                        fn = hist_field_u64;
                break;
        case 4:
                if (field_is_signed)
                        fn = hist_field_s32;
                else
                        fn = hist_field_u32;
                break;
        case 2:
                if (field_is_signed)
                        fn = hist_field_s16;
                else
                        fn = hist_field_u16;
                break;
        case 1:
                if (field_is_signed)
                        fn = hist_field_s8;
                else
                        fn = hist_field_u8;
                break;
        }

        return fn;
}

static int parse_map_size(char *str)
{
        unsigned long size, map_bits;
        int ret;

        ret = kstrtoul(str, 0, &size);
        if (ret)
                goto out;

        map_bits = ilog2(roundup_pow_of_two(size));
        if (map_bits < TRACING_MAP_BITS_MIN ||
            map_bits > TRACING_MAP_BITS_MAX)
                ret = -EINVAL;
        else
                ret = map_bits;
 out:
        return ret;
}

static void destroy_hist_trigger_attrs(struct hist_trigger_attrs *attrs)
{
        unsigned int i;

        if (!attrs)
                return;

        for (i = 0; i < attrs->n_assignments; i++)
                kfree(attrs->assignment_str[i]);

        for (i = 0; i < attrs->n_actions; i++)
                kfree(attrs->action_str[i]);

        kfree(attrs->name);
        kfree(attrs->sort_key_str);
        kfree(attrs->keys_str);
        kfree(attrs->vals_str);
        kfree(attrs->clock);
        kfree(attrs);
}

static int parse_action(char *str, struct hist_trigger_attrs *attrs)
{
        int ret = -EINVAL;

        if (attrs->n_actions >= HIST_ACTIONS_MAX)
                return ret;

        if ((str_has_prefix(str, "onmatch(")) ||
            (str_has_prefix(str, "onmax(")) ||
            (str_has_prefix(str, "onchange("))) {
                attrs->action_str[attrs->n_actions] = kstrdup(str, GFP_KERNEL);
                if (!attrs->action_str[attrs->n_actions]) {
                        ret = -ENOMEM;
                        return ret;
                }
                attrs->n_actions++;
                ret = 0;
        }
        return ret;
}

static int parse_assignment(struct trace_array *tr,
                            char *str, struct hist_trigger_attrs *attrs)
{
        int len, ret = 0;

        if ((len = str_has_prefix(str, "key=")) ||
            (len = str_has_prefix(str, "keys="))) {
                attrs->keys_str = kstrdup(str + len, GFP_KERNEL);
                if (!attrs->keys_str) {
                        ret = -ENOMEM;
                        goto out;
                }
        } else if ((len = str_has_prefix(str, "val=")) ||
                   (len = str_has_prefix(str, "vals=")) ||
                   (len = str_has_prefix(str, "values="))) {
                attrs->vals_str = kstrdup(str + len, GFP_KERNEL);
                if (!attrs->vals_str) {
                        ret = -ENOMEM;
                        goto out;
                }
        } else if ((len = str_has_prefix(str, "sort="))) {
                attrs->sort_key_str = kstrdup(str + len, GFP_KERNEL);
                if (!attrs->sort_key_str) {
                        ret = -ENOMEM;
                        goto out;
                }
        } else if (str_has_prefix(str, "name=")) {
                attrs->name = kstrdup(str, GFP_KERNEL);
                if (!attrs->name) {
                        ret = -ENOMEM;
                        goto out;
                }
        } else if ((len = str_has_prefix(str, "clock="))) {
                str += len;

                str = strstrip(str);
                attrs->clock = kstrdup(str, GFP_KERNEL);
                if (!attrs->clock) {
                        ret = -ENOMEM;
                        goto out;
                }
        } else if ((len = str_has_prefix(str, "size="))) {
                int map_bits = parse_map_size(str + len);

                if (map_bits < 0) {
                        ret = map_bits;
                        goto out;
                }
                attrs->map_bits = map_bits;
        } else {
                char *assignment;

                if (attrs->n_assignments == TRACING_MAP_VARS_MAX) {
                        hist_err(tr, HIST_ERR_TOO_MANY_VARS, errpos(str));
                        ret = -EINVAL;
                        goto out;
                }

                assignment = kstrdup(str, GFP_KERNEL);
                if (!assignment) {
                        ret = -ENOMEM;
                        goto out;
                }

                attrs->assignment_str[attrs->n_assignments++] = assignment;
        }
 out:
        return ret;
}

static struct hist_trigger_attrs *
parse_hist_trigger_attrs(struct trace_array *tr, char *trigger_str)
{
        struct hist_trigger_attrs *attrs;
        int ret = 0;

        attrs = kzalloc(sizeof(*attrs), GFP_KERNEL);
        if (!attrs)
                return ERR_PTR(-ENOMEM);

        while (trigger_str) {
                char *str = strsep(&trigger_str, ":");
                char *rhs;

                rhs = strchr(str, '=');
                if (rhs) {
                        if (!strlen(++rhs)) {
                                ret = -EINVAL;
                                hist_err(tr, HIST_ERR_EMPTY_ASSIGNMENT, errpos(str));
                                goto free;
                        }
                        ret = parse_assignment(tr, str, attrs);
                        if (ret)
                                goto free;
                } else if (strcmp(str, "pause") == 0)
                        attrs->pause = true;
                else if ((strcmp(str, "cont") == 0) ||
                         (strcmp(str, "continue") == 0))
                        attrs->cont = true;
                else if (strcmp(str, "clear") == 0)
                        attrs->clear = true;
                else {
                        ret = parse_action(str, attrs);
                        if (ret)
                                goto free;
                }
        }

        if (!attrs->keys_str) {
                ret = -EINVAL;
                goto free;
        }

        if (!attrs->clock) {
                attrs->clock = kstrdup("global", GFP_KERNEL);
                if (!attrs->clock) {
                        ret = -ENOMEM;
                        goto free;
                }
        }

        return attrs;
 free:
        destroy_hist_trigger_attrs(attrs);

        return ERR_PTR(ret);
}

static inline void save_comm(char *comm, struct task_struct *task)
{
        if (!task->pid) {
                strcpy(comm, "<idle>");
                return;
        }

        if (WARN_ON_ONCE(task->pid < 0)) {
                strcpy(comm, "<XXX>");
                return;
        }

        strncpy(comm, task->comm, TASK_COMM_LEN);
}

static void hist_elt_data_free(struct hist_elt_data *elt_data)
{
        unsigned int i;

        for (i = 0; i < SYNTH_FIELDS_MAX; i++)
                kfree(elt_data->field_var_str[i]);

        kfree(elt_data->comm);
        kfree(elt_data);
}

static void hist_trigger_elt_data_free(struct tracing_map_elt *elt)
{
        struct hist_elt_data *elt_data = elt->private_data;

        hist_elt_data_free(elt_data);
}

static int hist_trigger_elt_data_alloc(struct tracing_map_elt *elt)
{
        struct hist_trigger_data *hist_data = elt->map->private_data;
        unsigned int size = TASK_COMM_LEN;
        struct hist_elt_data *elt_data;
        struct hist_field *key_field;
        unsigned int i, n_str;

        elt_data = kzalloc(sizeof(*elt_data), GFP_KERNEL);
        if (!elt_data)
                return -ENOMEM;

        for_each_hist_key_field(i, hist_data) {
                key_field = hist_data->fields[i];

                if (key_field->flags & HIST_FIELD_FL_EXECNAME) {
                        elt_data->comm = kzalloc(size, GFP_KERNEL);
                        if (!elt_data->comm) {
                                kfree(elt_data);
                                return -ENOMEM;
                        }
                        break;
                }
        }

        n_str = hist_data->n_field_var_str + hist_data->n_save_var_str +
                hist_data->n_var_str;
        if (n_str > SYNTH_FIELDS_MAX) {
                hist_elt_data_free(elt_data);
                return -EINVAL;
        }

        BUILD_BUG_ON(STR_VAR_LEN_MAX & (sizeof(u64) - 1));

        size = STR_VAR_LEN_MAX;

        for (i = 0; i < n_str; i++) {
                elt_data->field_var_str[i] = kzalloc(size, GFP_KERNEL);
                if (!elt_data->field_var_str[i]) {
                        hist_elt_data_free(elt_data);
                        return -ENOMEM;
                }
        }

        elt->private_data = elt_data;

        return 0;
}

static void hist_trigger_elt_data_init(struct tracing_map_elt *elt)
{
        struct hist_elt_data *elt_data = elt->private_data;

        if (elt_data->comm)
                save_comm(elt_data->comm, current);
}

static const struct tracing_map_ops hist_trigger_elt_data_ops = {
        .elt_alloc      = hist_trigger_elt_data_alloc,
        .elt_free       = hist_trigger_elt_data_free,
        .elt_init       = hist_trigger_elt_data_init,
};

static const char *get_hist_field_flags(struct hist_field *hist_field)
{
        const char *flags_str = NULL;

        if (hist_field->flags & HIST_FIELD_FL_HEX)
                flags_str = "hex";
        else if (hist_field->flags & HIST_FIELD_FL_SYM)
                flags_str = "sym";
        else if (hist_field->flags & HIST_FIELD_FL_SYM_OFFSET)
                flags_str = "sym-offset";
        else if (hist_field->flags & HIST_FIELD_FL_EXECNAME)
                flags_str = "execname";
        else if (hist_field->flags & HIST_FIELD_FL_SYSCALL)
                flags_str = "syscall";
        else if (hist_field->flags & HIST_FIELD_FL_LOG2)
                flags_str = "log2";
        else if (hist_field->flags & HIST_FIELD_FL_TIMESTAMP_USECS)
                flags_str = "usecs";

        return flags_str;
}

static void expr_field_str(struct hist_field *field, char *expr)
{
        if (field->flags & HIST_FIELD_FL_VAR_REF)
                strcat(expr, "$");

        strcat(expr, hist_field_name(field, 0));

        if (field->flags && !(field->flags & HIST_FIELD_FL_VAR_REF)) {
                const char *flags_str = get_hist_field_flags(field);

                if (flags_str) {
                        strcat(expr, ".");
                        strcat(expr, flags_str);
                }
        }
}

static char *expr_str(struct hist_field *field, unsigned int level)
{
        char *expr;

        if (level > 1)
                return NULL;

        expr = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
        if (!expr)
                return NULL;

        if (!field->operands[0]) {
                expr_field_str(field, expr);
                return expr;
        }

        if (field->operator == FIELD_OP_UNARY_MINUS) {
                char *subexpr;

                strcat(expr, "-(");
                subexpr = expr_str(field->operands[0], ++level);
                if (!subexpr) {
                        kfree(expr);
                        return NULL;
                }
                strcat(expr, subexpr);
                strcat(expr, ")");

                kfree(subexpr);

                return expr;
        }

        expr_field_str(field->operands[0], expr);

        switch (field->operator) {
        case FIELD_OP_MINUS:
                strcat(expr, "-");
                break;
        case FIELD_OP_PLUS:
                strcat(expr, "+");
                break;
        default:
                kfree(expr);
                return NULL;
        }

        expr_field_str(field->operands[1], expr);

        return expr;
}

static int contains_operator(char *str)
{
        enum field_op_id field_op = FIELD_OP_NONE;
        char *op;

        op = strpbrk(str, "+-");
        if (!op)
                return FIELD_OP_NONE;

        switch (*op) {
        case '-':
                if (*str == '-')
                        field_op = FIELD_OP_UNARY_MINUS;
                else
                        field_op = FIELD_OP_MINUS;
                break;
        case '+':
                field_op = FIELD_OP_PLUS;
                break;
        default:
                break;
        }

        return field_op;
}

static void get_hist_field(struct hist_field *hist_field)
{
        hist_field->ref++;
}

static void __destroy_hist_field(struct hist_field *hist_field)
{
        if (--hist_field->ref > 1)
                return;

        kfree(hist_field->var.name);
        kfree(hist_field->name);
        kfree(hist_field->type);

        kfree(hist_field->system);
        kfree(hist_field->event_name);

        kfree(hist_field);
}

static void destroy_hist_field(struct hist_field *hist_field,
                               unsigned int level)
{
        unsigned int i;

        if (level > 3)
                return;

        if (!hist_field)
                return;

        if (hist_field->flags & HIST_FIELD_FL_VAR_REF)
                return; /* var refs will be destroyed separately */

        for (i = 0; i < HIST_FIELD_OPERANDS_MAX; i++)
                destroy_hist_field(hist_field->operands[i], level + 1);

        __destroy_hist_field(hist_field);
}

static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
                                            struct ftrace_event_field *field,
                                            unsigned long flags,
                                            char *var_name)
{
        struct hist_field *hist_field;

        if (field && is_function_field(field))
                return NULL;

        hist_field = kzalloc(sizeof(struct hist_field), GFP_KERNEL);
        if (!hist_field)
                return NULL;

        hist_field->ref = 1;

        hist_field->hist_data = hist_data;

        if (flags & HIST_FIELD_FL_EXPR || flags & HIST_FIELD_FL_ALIAS)
                goto out; /* caller will populate */

        if (flags & HIST_FIELD_FL_VAR_REF) {
                hist_field->fn = hist_field_var_ref;
                goto out;
        }

        if (flags & HIST_FIELD_FL_HITCOUNT) {
                hist_field->fn = hist_field_counter;
                hist_field->size = sizeof(u64);
                hist_field->type = kstrdup("u64", GFP_KERNEL);
                if (!hist_field->type)
                        goto free;
                goto out;
        }

        if (flags & HIST_FIELD_FL_STACKTRACE) {
                hist_field->fn = hist_field_none;
                goto out;
        }

        if (flags & HIST_FIELD_FL_LOG2) {
                unsigned long fl = flags & ~HIST_FIELD_FL_LOG2;
                hist_field->fn = hist_field_log2;
                hist_field->operands[0] = create_hist_field(hist_data, field, fl, NULL);
                hist_field->size = hist_field->operands[0]->size;
                hist_field->type = kstrdup(hist_field->operands[0]->type, GFP_KERNEL);
                if (!hist_field->type)
                        goto free;
                goto out;
        }

        if (flags & HIST_FIELD_FL_TIMESTAMP) {
                hist_field->fn = hist_field_timestamp;
                hist_field->size = sizeof(u64);
                hist_field->type = kstrdup("u64", GFP_KERNEL);
                if (!hist_field->type)
                        goto free;
                goto out;
        }

        if (flags & HIST_FIELD_FL_CPU) {
                hist_field->fn = hist_field_cpu;
                hist_field->size = sizeof(int);
                hist_field->type = kstrdup("unsigned int", GFP_KERNEL);
                if (!hist_field->type)
                        goto free;
                goto out;
        }

        if (WARN_ON_ONCE(!field))
                goto out;

        if (is_string_field(field)) {
                flags |= HIST_FIELD_FL_STRING;

                hist_field->size = MAX_FILTER_STR_VAL;
                hist_field->type = kstrdup(field->type, GFP_KERNEL);
                if (!hist_field->type)
                        goto free;

                if (field->filter_type == FILTER_STATIC_STRING)
                        hist_field->fn = hist_field_string;
                else if (field->filter_type == FILTER_DYN_STRING)
                        hist_field->fn = hist_field_dynstring;
                else
                        hist_field->fn = hist_field_pstring;
        } else {
                hist_field->size = field->size;
                hist_field->is_signed = field->is_signed;
                hist_field->type = kstrdup(field->type, GFP_KERNEL);
                if (!hist_field->type)
                        goto free;

                hist_field->fn = select_value_fn(field->size,
                                                 field->is_signed);
                if (!hist_field->fn) {
                        destroy_hist_field(hist_field, 0);
                        return NULL;
                }
        }
 out:
        hist_field->field = field;
        hist_field->flags = flags;

        if (var_name) {
                hist_field->var.name = kstrdup(var_name, GFP_KERNEL);
                if (!hist_field->var.name)
                        goto free;
        }

        return hist_field;
 free:
        destroy_hist_field(hist_field, 0);
        return NULL;
}

static void destroy_hist_fields(struct hist_trigger_data *hist_data)
{
        unsigned int i;

        for (i = 0; i < HIST_FIELDS_MAX; i++) {
                if (hist_data->fields[i]) {
                        destroy_hist_field(hist_data->fields[i], 0);
                        hist_data->fields[i] = NULL;
                }
        }

        for (i = 0; i < hist_data->n_var_refs; i++) {
                WARN_ON(!(hist_data->var_refs[i]->flags & HIST_FIELD_FL_VAR_REF));
                __destroy_hist_field(hist_data->var_refs[i]);
                hist_data->var_refs[i] = NULL;
        }
}

static int init_var_ref(struct hist_field *ref_field,
                        struct hist_field *var_field,
                        char *system, char *event_name)
{
        int err = 0;

        ref_field->var.idx = var_field->var.idx;
        ref_field->var.hist_data = var_field->hist_data;
        ref_field->size = var_field->size;
        ref_field->is_signed = var_field->is_signed;
        ref_field->flags |= var_field->flags &
                (HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS);

        if (system) {
                ref_field->system = kstrdup(system, GFP_KERNEL);
                if (!ref_field->system)
                        return -ENOMEM;
        }

        if (event_name) {
                ref_field->event_name = kstrdup(event_name, GFP_KERNEL);
                if (!ref_field->event_name) {
                        err = -ENOMEM;
                        goto free;
                }
        }

        if (var_field->var.name) {
                ref_field->name = kstrdup(var_field->var.name, GFP_KERNEL);
                if (!ref_field->name) {
                        err = -ENOMEM;
                        goto free;
                }
        } else if (var_field->name) {
                ref_field->name = kstrdup(var_field->name, GFP_KERNEL);
                if (!ref_field->name) {
                        err = -ENOMEM;
                        goto free;
                }
        }

        ref_field->type = kstrdup(var_field->type, GFP_KERNEL);
        if (!ref_field->type) {
                err = -ENOMEM;
                goto free;
        }
 out:
        return err;
 free:
        kfree(ref_field->system);
        kfree(ref_field->event_name);
        kfree(ref_field->name);

        goto out;
}

static int find_var_ref_idx(struct hist_trigger_data *hist_data,
                            struct hist_field *var_field)
{
        struct hist_field *ref_field;
        int i;

        for (i = 0; i < hist_data->n_var_refs; i++) {
                ref_field = hist_data->var_refs[i];
                if (ref_field->var.idx == var_field->var.idx &&
                    ref_field->var.hist_data == var_field->hist_data)
                        return i;
        }

        return -ENOENT;
}

/**
 * create_var_ref - Create a variable reference and attach it to trigger
 * @hist_data: The trigger that will be referencing the variable
 * @var_field: The VAR field to create a reference to
 * @system: The optional system string
 * @event_name: The optional event_name string
 *
 * Given a variable hist_field, create a VAR_REF hist_field that
 * represents a reference to it.
 *
 * This function also adds the reference to the trigger that
 * now references the variable.
 *
 * Return: The VAR_REF field if successful, NULL if not
 */
static struct hist_field *create_var_ref(struct hist_trigger_data *hist_data,
                                         struct hist_field *var_field,
                                         char *system, char *event_name)
{
        unsigned long flags = HIST_FIELD_FL_VAR_REF;
        struct hist_field *ref_field;
        int i;

        /* Check if the variable already exists */
        for (i = 0; i < hist_data->n_var_refs; i++) {
                ref_field = hist_data->var_refs[i];
                if (ref_field->var.idx == var_field->var.idx &&
                    ref_field->var.hist_data == var_field->hist_data) {
                        get_hist_field(ref_field);
                        return ref_field;
                }
        }

        ref_field = create_hist_field(var_field->hist_data, NULL, flags, NULL);
        if (ref_field) {
                if (init_var_ref(ref_field, var_field, system, event_name)) {
                        destroy_hist_field(ref_field, 0);
                        return NULL;
                }

                hist_data->var_refs[hist_data->n_var_refs] = ref_field;
                ref_field->var_ref_idx = hist_data->n_var_refs++;
        }

        return ref_field;
}

static bool is_var_ref(char *var_name)
{
        if (!var_name || strlen(var_name) < 2 || var_name[0] != '$')
                return false;

        return true;
}

static char *field_name_from_var(struct hist_trigger_data *hist_data,
                                 char *var_name)
{
        char *name, *field;
        unsigned int i;

        for (i = 0; i < hist_data->attrs->var_defs.n_vars; i++) {
                name = hist_data->attrs->var_defs.name[i];

                if (strcmp(var_name, name) == 0) {
                        field = hist_data->attrs->var_defs.expr[i];
                        if (contains_operator(field) || is_var_ref(field))
                                continue;
                        return field;
                }
        }

        return NULL;
}

static char *local_field_var_ref(struct hist_trigger_data *hist_data,
                                 char *system, char *event_name,
                                 char *var_name)
{
        struct trace_event_call *call;

        if (system && event_name) {
                call = hist_data->event_file->event_call;

                if (strcmp(system, call->class->system) != 0)
                        return NULL;

                if (strcmp(event_name, trace_event_name(call)) != 0)
                        return NULL;
        }

        if (!!system != !!event_name)
                return NULL;

        if (!is_var_ref(var_name))
                return NULL;

        var_name++;

        return field_name_from_var(hist_data, var_name);
}

static struct hist_field *parse_var_ref(struct hist_trigger_data *hist_data,
                                        char *system, char *event_name,
                                        char *var_name)
{
        struct hist_field *var_field = NULL, *ref_field = NULL;
        struct trace_array *tr = hist_data->event_file->tr;

        if (!is_var_ref(var_name))
                return NULL;

        var_name++;

        var_field = find_event_var(hist_data, system, event_name, var_name);
        if (var_field)
                ref_field = create_var_ref(hist_data, var_field,
                                           system, event_name);

        if (!ref_field)
                hist_err(tr, HIST_ERR_VAR_NOT_FOUND, errpos(var_name));

        return ref_field;
}

static struct ftrace_event_field *
parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
            char *field_str, unsigned long *flags)
{
        struct ftrace_event_field *field = NULL;
        char *field_name, *modifier, *str;
        struct trace_array *tr = file->tr;

        modifier = str = kstrdup(field_str, GFP_KERNEL);
        if (!modifier)
                return ERR_PTR(-ENOMEM);

        field_name = strsep(&modifier, ".");
        if (modifier) {
                if (strcmp(modifier, "hex") == 0)
                        *flags |= HIST_FIELD_FL_HEX;
                else if (strcmp(modifier, "sym") == 0)
                        *flags |= HIST_FIELD_FL_SYM;
                else if (strcmp(modifier, "sym-offset") == 0)
                        *flags |= HIST_FIELD_FL_SYM_OFFSET;
                else if ((strcmp(modifier, "execname") == 0) &&
                         (strcmp(field_name, "common_pid") == 0))
                        *flags |= HIST_FIELD_FL_EXECNAME;
                else if (strcmp(modifier, "syscall") == 0)
                        *flags |= HIST_FIELD_FL_SYSCALL;
                else if (strcmp(modifier, "log2") == 0)
                        *flags |= HIST_FIELD_FL_LOG2;
                else if (strcmp(modifier, "usecs") == 0)
                        *flags |= HIST_FIELD_FL_TIMESTAMP_USECS;
                else {
                        hist_err(tr, HIST_ERR_BAD_FIELD_MODIFIER, errpos(modifier));
                        field = ERR_PTR(-EINVAL);
                        goto out;
                }
        }

        if (strcmp(field_name, "common_timestamp") == 0) {
                *flags |= HIST_FIELD_FL_TIMESTAMP;
                hist_data->enable_timestamps = true;
                if (*flags & HIST_FIELD_FL_TIMESTAMP_USECS)
                        hist_data->attrs->ts_in_usecs = true;
        } else if (strcmp(field_name, "cpu") == 0)
                *flags |= HIST_FIELD_FL_CPU;
        else {
                field = trace_find_event_field(file->event_call, field_name);
                if (!field || !field->size) {
                        hist_err(tr, HIST_ERR_FIELD_NOT_FOUND, errpos(field_name));
                        field = ERR_PTR(-EINVAL);
                        goto out;
                }
        }
 out:
        kfree(str);

        return field;
}

static struct hist_field *create_alias(struct hist_trigger_data *hist_data,
                                       struct hist_field *var_ref,
                                       char *var_name)
{
        struct hist_field *alias = NULL;
        unsigned long flags = HIST_FIELD_FL_ALIAS | HIST_FIELD_FL_VAR;

        alias = create_hist_field(hist_data, NULL, flags, var_name);
        if (!alias)
                return NULL;

        alias->fn = var_ref->fn;
        alias->operands[0] = var_ref;

        if (init_var_ref(alias, var_ref, var_ref->system, var_ref->event_name)) {
                destroy_hist_field(alias, 0);

                return NULL;
        }

        alias->var_ref_idx = var_ref->var_ref_idx;

        return alias;
}

static struct hist_field *parse_atom(struct hist_trigger_data *hist_data,
                                     struct trace_event_file *file, char *str,
                                     unsigned long *flags, char *var_name)
{
        char *s, *ref_system = NULL, *ref_event = NULL, *ref_var = str;
        struct ftrace_event_field *field = NULL;
        struct hist_field *hist_field = NULL;
        int ret = 0;

        s = strchr(str, '.');
        if (s) {
                s = strchr(++s, '.');
                if (s) {
                        ref_system = strsep(&str, ".");
                        if (!str) {
                                ret = -EINVAL;
                                goto out;
                        }
                        ref_event = strsep(&str, ".");
                        if (!str) {
                                ret = -EINVAL;
                                goto out;
                        }
                        ref_var = str;
                }
        }

        s = local_field_var_ref(hist_data, ref_system, ref_event, ref_var);
        if (!s) {
                hist_field = parse_var_ref(hist_data, ref_system,
                                           ref_event, ref_var);
                if (hist_field) {
                        if (var_name) {
                                hist_field = create_alias(hist_data, hist_field, var_name);
                                if (!hist_field) {
                                        ret = -ENOMEM;
                                        goto out;
                                }
                        }
                        return hist_field;
                }
        } else
                str = s;

        field = parse_field(hist_data, file, str, flags);
        if (IS_ERR(field)) {
                ret = PTR_ERR(field);
                goto out;
        }

        hist_field = create_hist_field(hist_data, field, *flags, var_name);
        if (!hist_field) {
                ret = -ENOMEM;
                goto out;
        }

        return hist_field;
 out:
        return ERR_PTR(ret);
}

static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
                                     struct trace_event_file *file,
                                     char *str, unsigned long flags,
                                     char *var_name, unsigned int level);

static struct hist_field *parse_unary(struct hist_trigger_data *hist_data,
                                      struct trace_event_file *file,
                                      char *str, unsigned long flags,
                                      char *var_name, unsigned int level)
{
        struct hist_field *operand1, *expr = NULL;
        unsigned long operand_flags;
        int ret = 0;
        char *s;

        /* we support only -(xxx) i.e. explicit parens required */

        if (level > 3) {
                hist_err(file->tr, HIST_ERR_TOO_MANY_SUBEXPR, errpos(str));
                ret = -EINVAL;
                goto free;
        }

        str++; /* skip leading '-' */

        s = strchr(str, '(');
        if (s)
                str++;
        else {
                ret = -EINVAL;
                goto free;
        }

        s = strrchr(str, ')');
        if (s)
                *s = '\0';
        else {
                ret = -EINVAL; /* no closing ')' */
                goto free;
        }

        flags |= HIST_FIELD_FL_EXPR;
        expr = create_hist_field(hist_data, NULL, flags, var_name);
        if (!expr) {
                ret = -ENOMEM;
                goto free;
        }

        operand_flags = 0;
        operand1 = parse_expr(hist_data, file, str, operand_flags, NULL, ++level);
        if (IS_ERR(operand1)) {
                ret = PTR_ERR(operand1);
                goto free;
        }

        expr->flags |= operand1->flags &
                (HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS);
        expr->fn = hist_field_unary_minus;
        expr->operands[0] = operand1;
        expr->operator = FIELD_OP_UNARY_MINUS;
        expr->name = expr_str(expr, 0);
        expr->type = kstrdup(operand1->type, GFP_KERNEL);
        if (!expr->type) {
                ret = -ENOMEM;
                goto free;
        }

        return expr;
 free:
        destroy_hist_field(expr, 0);
        return ERR_PTR(ret);
}

static int check_expr_operands(struct trace_array *tr,
                               struct hist_field *operand1,
                               struct hist_field *operand2)
{
        unsigned long operand1_flags = operand1->flags;
        unsigned long operand2_flags = operand2->flags;

        if ((operand1_flags & HIST_FIELD_FL_VAR_REF) ||
            (operand1_flags & HIST_FIELD_FL_ALIAS)) {
                struct hist_field *var;

                var = find_var_field(operand1->var.hist_data, operand1->name);
                if (!var)
                        return -EINVAL;
                operand1_flags = var->flags;
        }

        if ((operand2_flags & HIST_FIELD_FL_VAR_REF) ||
            (operand2_flags & HIST_FIELD_FL_ALIAS)) {
                struct hist_field *var;

                var = find_var_field(operand2->var.hist_data, operand2->name);
                if (!var)
                        return -EINVAL;
                operand2_flags = var->flags;
        }

        if ((operand1_flags & HIST_FIELD_FL_TIMESTAMP_USECS) !=
            (operand2_flags & HIST_FIELD_FL_TIMESTAMP_USECS)) {
                hist_err(tr, HIST_ERR_TIMESTAMP_MISMATCH, 0);
                return -EINVAL;
        }

        return 0;
}

static struct hist_field *parse_expr(struct hist_trigger_data *hist_data,
                                     struct trace_event_file *file,
                                     char *str, unsigned long flags,
                                     char *var_name, unsigned int level)
{
        struct hist_field *operand1 = NULL, *operand2 = NULL, *expr = NULL;
        unsigned long operand_flags;
        int field_op, ret = -EINVAL;
        char *sep, *operand1_str;

        if (level > 3) {
                hist_err(file->tr, HIST_ERR_TOO_MANY_SUBEXPR, errpos(str));
                return ERR_PTR(-EINVAL);
        }

        field_op = contains_operator(str);

        if (field_op == FIELD_OP_NONE)
                return parse_atom(hist_data, file, str, &flags, var_name);

        if (field_op == FIELD_OP_UNARY_MINUS)
                return parse_unary(hist_data, file, str, flags, var_name, ++level);

        switch (field_op) {
        case FIELD_OP_MINUS:
                sep = "-";
                break;
        case FIELD_OP_PLUS:
                sep = "+";
                break;
        default:
                goto free;
        }

        operand1_str = strsep(&str, sep);
        if (!operand1_str || !str)
                goto free;

        operand_flags = 0;
        operand1 = parse_atom(hist_data, file, operand1_str,
                              &operand_flags, NULL);
        if (IS_ERR(operand1)) {
                ret = PTR_ERR(operand1);
                operand1 = NULL;
                goto free;
        }

        /* rest of string could be another expression e.g. b+c in a+b+c */
        operand_flags = 0;
        operand2 = parse_expr(hist_data, file, str, operand_flags, NULL, ++level);
        if (IS_ERR(operand2)) {
                ret = PTR_ERR(operand2);
                operand2 = NULL;
                goto free;
        }

        ret = check_expr_operands(file->tr, operand1, operand2);
        if (ret)
                goto free;

        flags |= HIST_FIELD_FL_EXPR;

        flags |= operand1->flags &
                (HIST_FIELD_FL_TIMESTAMP | HIST_FIELD_FL_TIMESTAMP_USECS);

        expr = create_hist_field(hist_data, NULL, flags, var_name);
        if (!expr) {
                ret = -ENOMEM;
                goto free;
        }

        operand1->read_once = true;
        operand2->read_once = true;

        expr->operands[0] = operand1;
        expr->operands[1] = operand2;
        expr->operator = field_op;
        expr->name = expr_str(expr, 0);
        expr->type = kstrdup(operand1->type, GFP_KERNEL);
        if (!expr->type) {
                ret = -ENOMEM;
                goto free;
        }

        switch (field_op) {
        case FIELD_OP_MINUS:
                expr->fn = hist_field_minus;
                break;
        case FIELD_OP_PLUS:
                expr->fn = hist_field_plus;
                break;
        default:
                ret = -EINVAL;
                goto free;
        }

        return expr;
 free:
        destroy_hist_field(operand1, 0);
        destroy_hist_field(operand2, 0);
        destroy_hist_field(expr, 0);

        return ERR_PTR(ret);
}

static char *find_trigger_filter(struct hist_trigger_data *hist_data,
                                 struct trace_event_file *file)
{
        struct event_trigger_data *test;

        lockdep_assert_held(&event_mutex);

        list_for_each_entry(test, &file->triggers, list) {
                if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
                        if (test->private_data == hist_data)
                                return test->filter_str;
                }
        }

        return NULL;
}

static struct event_command trigger_hist_cmd;
static int event_hist_trigger_func(struct event_command *cmd_ops,
                                   struct trace_event_file *file,
                                   char *glob, char *cmd, char *param);

static bool compatible_keys(struct hist_trigger_data *target_hist_data,
                            struct hist_trigger_data *hist_data,
                            unsigned int n_keys)
{
        struct hist_field *target_hist_field, *hist_field;
        unsigned int n, i, j;

        if (hist_data->n_fields - hist_data->n_vals != n_keys)
                return false;

        i = hist_data->n_vals;
        j = target_hist_data->n_vals;

        for (n = 0; n < n_keys; n++) {
                hist_field = hist_data->fields[i + n];
                target_hist_field = target_hist_data->fields[j + n];

                if (strcmp(hist_field->type, target_hist_field->type) != 0)
                        return false;
                if (hist_field->size != target_hist_field->size)
                        return false;
                if (hist_field->is_signed != target_hist_field->is_signed)
                        return false;
        }

        return true;
}

static struct hist_trigger_data *
find_compatible_hist(struct hist_trigger_data *target_hist_data,
                     struct trace_event_file *file)
{
        struct hist_trigger_data *hist_data;
        struct event_trigger_data *test;
        unsigned int n_keys;

        lockdep_assert_held(&event_mutex);

        n_keys = target_hist_data->n_fields - target_hist_data->n_vals;

        list_for_each_entry(test, &file->triggers, list) {
                if (test->cmd_ops->trigger_type == ETT_EVENT_HIST) {
                        hist_data = test->private_data;

                        if (compatible_keys(target_hist_data, hist_data, n_keys))
                                return hist_data;
                }
        }

        return NULL;
}

static struct trace_event_file *event_file(struct trace_array *tr,
                                           char *system, char *event_name)
{
        struct trace_event_file *file;

        file = __find_event_file(tr, system, event_name);
        if (!file)
                return ERR_PTR(-EINVAL);

        return file;
}

static struct hist_field *
find_synthetic_field_var(struct hist_trigger_data *target_hist_data,
                         char *system, char *event_name, char *field_name)
{
        struct hist_field *event_var;
        char *synthetic_name;

        synthetic_name = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
        if (!synthetic_name)
                return ERR_PTR(-ENOMEM);

        strcpy(synthetic_name, "synthetic_");
        strcat(synthetic_name, field_name);

        event_var = find_event_var(target_hist_data, system, event_name, synthetic_name);

        kfree(synthetic_name);

        return event_var;
}

/**
 * create_field_var_hist - Automatically create a histogram and var for a field
 * @target_hist_data: The target hist trigger
 * @subsys_name: Optional subsystem name
 * @event_name: Optional event name
 * @field_name: The name of the field (and the resulting variable)
 *
 * Hist trigger actions fetch data from variables, not directly from
 * events.  However, for convenience, users are allowed to directly
 * specify an event field in an action, which will be automatically
 * converted into a variable on their behalf.

 * If a user specifies a field on an event that isn't the event the
 * histogram currently being defined (the target event histogram), the
 * only way that can be accomplished is if a new hist trigger is
 * created and the field variable defined on that.
 *
 * This function creates a new histogram compatible with the target
 * event (meaning a histogram with the same key as the target
 * histogram), and creates a variable for the specified field, but
 * with 'synthetic_' prepended to the variable name in order to avoid
 * collision with normal field variables.
 *
 * Return: The variable created for the field.
 */
static struct hist_field *
create_field_var_hist(struct hist_trigger_data *target_hist_data,
                      char *subsys_name, char *event_name, char *field_name)
{
        struct trace_array *tr = target_hist_data->event_file->tr;
        struct hist_field *event_var = ERR_PTR(-EINVAL);
        struct hist_trigger_data *hist_data;
        unsigned int i, n, first = true;
        struct field_var_hist *var_hist;
        struct trace_event_file *file;
        struct hist_field *key_field;
        char *saved_filter;
        char *cmd;
        int ret;

        if (target_hist_data->n_field_var_hists >= SYNTH_FIELDS_MAX) {
                hist_err(tr, HIST_ERR_TOO_MANY_FIELD_VARS, errpos(field_name));
                return ERR_PTR(-EINVAL);
        }

        file = event_file(tr, subsys_name, event_name);

        if (IS_ERR(file)) {
                hist_err(tr, HIST_ERR_EVENT_FILE_NOT_FOUND, errpos(field_name));
                ret = PTR_ERR(file);
                return ERR_PTR(ret);
        }

        /*
         * Look for a histogram compatible with target.  We'll use the
         * found histogram specification to create a new matching
         * histogram with our variable on it.  target_hist_data is not
         * yet a registered histogram so we can't use that.
         */
        hist_data = find_compatible_hist(target_hist_data, file);
        if (!hist_data) {
                hist_err(tr, HIST_ERR_HIST_NOT_FOUND, errpos(field_name));
                return ERR_PTR(-EINVAL);
        }

        /* See if a synthetic field variable has already been created */
        event_var = find_synthetic_field_var(target_hist_data, subsys_name,
                                             event_name, field_name);
        if (!IS_ERR_OR_NULL(event_var))
                return event_var;

        var_hist = kzalloc(sizeof(*var_hist), GFP_KERNEL);
        if (!var_hist)
                return ERR_PTR(-ENOMEM);

        cmd = kzalloc(MAX_FILTER_STR_VAL, GFP_KERNEL);
        if (!cmd) {
                kfree(var_hist);
                return ERR_PTR(-ENOMEM);
        }

        /* Use the same keys as the compatible histogram */
        strcat(cmd, "keys=");

        for_each_hist_key_field(i, hist_data) {
                key_field = hist_data->fields[i];
                if (!first)
                        strcat(cmd, ",");
                strcat(cmd, key_field->field->name);
                first = false;
        }

        /* Create the synthetic field variable specification */
        strcat(cmd, ":synthetic_");
        strcat(cmd, field_name);
        strcat(cmd, "=");
        strcat(cmd, field_name);

        /* Use the same filter as the compatible histogram */
        saved_filter = find_trigger_filter(hist_data, file);
        if (saved_filter) {
                strcat(cmd, " if ");
                strcat(cmd, saved_filter);
        }

        var_hist->cmd = kstrdup(cmd, GFP_KERNEL);
        if (!var_hist->cmd) {
                kfree(cmd);
                kfree(var_hist);
                return ERR_PTR(-ENOMEM);
        }

        /* Save the compatible histogram information */
        var_hist->hist_data = hist_data;

        /* Create the new histogram with our variable */
        ret = event_hist_trigger_func(&trigger_hist_cmd, file,
                                      "", "hist", cmd);
        if (ret) {
                kfree(cmd);
                kfree(var_hist->cmd);
                kfree(var_hist);
                hist_err(tr, HIST_ERR_HIST_CREATE_FAIL, errpos(field_name));
                return ERR_PTR(ret);
        }

        kfree(cmd);

        /* If we can't find the variable, something went wrong */
        event_var = find_synthetic_field_var(target_hist_data, subsys_name,
                                             event_name, field_name);
        if (IS_ERR_OR_NULL(event_var)) {
                kfree(var_hist->cmd);
                kfree(var_hist);
                hist_err(tr, HIST_ERR_SYNTH_VAR_NOT_FOUND, errpos(field_name));
                return ERR_PTR(-EINVAL);
        }

        n = target_hist_data->n_field_var_hists;
        target_hist_data->field_var_hists[n] = var_hist;
        target_hist_data->n_field_var_hists++;

        return event_var;
}

static struct hist_field *
find_target_event_var(struct hist_trigger_data *hist_data,
                      char *subsys_name, char *event_name, char *var_name)
{
        struct trace_event_file *file = hist_data->event_file;
        struct hist_field *hist_field = NULL;

        if (subsys_name) {
                struct trace_event_call *call;

                if (!event_name)
                        return NULL;

                call = file->event_call;

                if (strcmp(subsys_name, call->class->system) != 0)
                        return NULL;

                if (strcmp(event_name, trace_event_name(call)) != 0)
                        return NULL;
        }

        hist_field = find_var_field(hist_data, var_name);

        return hist_field;
}

static inline void __update_field_vars(struct tracing_map_elt *elt,
                                       struct ring_buffer_event *rbe,
                                       void *rec,
                                       struct field_var **field_vars,
                                       unsigned int n_field_vars,
                                       unsigned int field_var_str_start)
{
        struct hist_elt_data *elt_data = elt->private_data;
        unsigned int i, j, var_idx;
        u64 var_val;

        for (i = 0, j = field_var_str_start; i < n_field_vars; i++) {
                struct field_var *field_var = field_vars[i];
                struct hist_field *var = field_var->var;
                struct hist_field *val = field_var->val;

                var_val = val->fn(val, elt, rbe, rec);
                var_idx = var->var.idx;

                if (val->flags & HIST_FIELD_FL_STRING) {
                        char *str = elt_data->field_var_str[j++];
                        char *val_str = (char *)(uintptr_t)var_val;

                        strscpy(str, val_str, STR_VAR_LEN_MAX);
                        var_val = (u64)(uintptr_t)str;
                }
                tracing_map_set_var(elt, var_idx, var_val);
        }
}

static void update_field_vars(struct hist_trigger_data *hist_data,
                              struct tracing_map_elt *elt,
                              struct ring_buffer_event *rbe,
                              void *rec)
{
        __update_field_vars(elt, rbe, rec, hist_data->field_vars,
                            hist_data->n_field_vars, 0);
}

static void save_track_data_vars(struct hist_trigger_data *hist_data,
                                 struct tracing_map_elt *elt, void *rec,
                                 struct ring_buffer_event *rbe, void *key,
                                 struct action_data *data, u64 *var_ref_vals)
{
        __update_field_vars(elt, rbe, rec, hist_data->save_vars,
                            hist_data->n_save_vars, hist_data->n_field_var_str);
}

static struct hist_field *create_var(struct hist_trigger_data *hist_data,
                                     struct trace_event_file *file,
                                     char *name, int size, const char *type)
{
        struct hist_field *var;
        int idx;

        if (find_var(hist_data, file, name) && !hist_data->remove) {
                var = ERR_PTR(-EINVAL);
                goto out;
        }

        var = kzalloc(sizeof(struct hist_field), GFP_KERNEL);
        if (!var) {
                var = ERR_PTR(-ENOMEM);
                goto out;
        }

        idx = tracing_map_add_var(hist_data->map);
        if (idx < 0) {
                kfree(var);
                var = ERR_PTR(-EINVAL);
                goto out;
        }

        var->ref = 1;
        var->flags = HIST_FIELD_FL_VAR;
        var->var.idx = idx;
        var->var.hist_data = var->hist_data = hist_data;
        var->size = size;
        var->var.name = kstrdup(name, GFP_KERNEL);
        var->type = kstrdup(type, GFP_KERNEL);
        if (!var->var.name || !var->type) {
                kfree(var->var.name);
                kfree(var->type);
                kfree(var);
                var = ERR_PTR(-ENOMEM);
        }
 out:
        return var;
}

static struct field_var *create_field_var(struct hist_trigger_data *hist_data,
                                          struct trace_event_file *file,
                                          char *field_name)
{
        struct hist_field *val = NULL, *var = NULL;
        unsigned long flags = HIST_FIELD_FL_VAR;
        struct trace_array *tr = file->tr;
        struct field_var *field_var;
        int ret = 0;

        if (hist_data->n_field_vars >= SYNTH_FIELDS_MAX) {
                hist_err(tr, HIST_ERR_TOO_MANY_FIELD_VARS, errpos(field_name));
                ret = -EINVAL;
                goto err;
        }

        val = parse_atom(hist_data, file, field_name, &flags, NULL);
        if (IS_ERR(val)) {
                hist_err(tr, HIST_ERR_FIELD_VAR_PARSE_FAIL, errpos(field_name));
                ret = PTR_ERR(val);
                goto err;
        }

        var = create_var(hist_data, file, field_name, val->size, val->type);
        if (IS_ERR(var)) {
                hist_err(tr, HIST_ERR_VAR_CREATE_FIND_FAIL, errpos(field_name));
                kfree(val);
                ret = PTR_ERR(var);
                goto err;
        }

        field_var = kzalloc(sizeof(struct field_var), GFP_KERNEL);
        if (!field_var) {
                kfree(val);
                kfree(var);
                ret =  -ENOMEM;
                goto err;
        }

        field_var->var = var;
        field_var->val = val;
 out:
        return field_var;
 err:
        field_var = ERR_PTR(ret);
        goto out;
}

/**
 * create_target_field_var - Automatically create a variable for a field
 * @target_hist_data: The target hist trigger
 * @subsys_name: Optional subsystem name
 * @event_name: Optional event name
 * @var_name: The name of the field (and the resulting variable)
 *
 * Hist trigger actions fetch data from variables, not directly from
 * events.  However, for convenience, users are allowed to directly
 * specify an event field in an action, which will be automatically
 * converted into a variable on their behalf.

 * This function creates a field variable with the name var_name on
 * the hist trigger currently being defined on the target event.  If
 * subsys_name and event_name are specified, this function simply
 * verifies that they do in fact match the target event subsystem and
 * event name.
 *
 * Return: The variable created for the field.
 */
static struct field_var *
create_target_field_var(struct hist_trigger_data *target_hist_data,
                        char *subsys_name, char *event_name, char *var_name)
{
        struct trace_event_file *file = target_hist_data->event_file;

        if (subsys_name) {
                struct trace_event_call *call;

                if (!event_name)
                        return NULL;

                call = file->event_call;

                if (strcmp(subsys_name, call->class->system) != 0)
                        return NULL;

                if (strcmp(event_name, trace_event_name(call)) != 0)
                        return NULL;
        }

        return create_field_var(target_hist_data, file, var_name);
}

static bool check_track_val_max(u64 track_val, u64 var_val)
{
        if (var_val <= track_val)
                return false;

        return true;
}

static bool check_track_val_changed(u64 track_val, u64 var_val)
{
        if (var_val == track_val)
                return false;

        return true;
}

static u64 get_track_val(struct hist_trigger_data *hist_data,
                         struct tracing_map_elt *elt,
                         struct action_data *data)
{
        unsigned int track_var_idx = data->track_data.track_var->var.idx;
        u64 track_val;

        track_val = tracing_map_read_var(elt, track_var_idx);

        return track_val;
}

static void save_track_val(struct hist_trigger_data *hist_data,
                           struct tracing_map_elt *elt,
                           struct action_data *data, u64 var_val)
{
        unsigned int track_var_idx = data->track_data.track_var->var.idx;

        tracing_map_set_var(elt, track_var_idx, var_val);
}

static void save_track_data(struct hist_trigger_data *hist_data,
                            struct tracing_map_elt *elt, void *rec,
                            struct ring_buffer_event *rbe, void *key,
                            struct action_data *data, u64 *var_ref_vals)
{
        if (data->track_data.save_data)
                data->track_data.save_data(hist_data, elt, rec, rbe, key, data, var_ref_vals);
}

static bool check_track_val(struct tracing_map_elt *elt,
                            struct action_data *data,
                            u64 var_val)
{
        struct hist_trigger_data *hist_data;
        u64 track_val;

        hist_data = data->track_data.track_var->hist_data;
        track_val = get_track_val(hist_data, elt, data);

        return data->track_data.check_val(track_val, var_val);
}

#ifdef CONFIG_TRACER_SNAPSHOT
static bool cond_snapshot_update(struct trace_array *tr, void *cond_data)
{
        /* called with tr->max_lock held */
        struct track_data *track_data = tr->cond_snapshot->cond_data;
        struct hist_elt_data *elt_data, *track_elt_data;
        struct snapshot_context *context = cond_data;
        struct action_data *action;
        u64 track_val;

        if (!track_data)
                return false;

        action = track_data->action_data;

        track_val = get_track_val(track_data->hist_data, context->elt,
                                  track_data->action_data);

        if (!action->track_data.check_val(track_data->track_val, track_val))
                return false;

        track_data->track_val = track_val;
        memcpy(track_data->key, context->key, track_data->key_len);

        elt_data = context->elt->private_data;
        track_elt_data = track_data->elt.private_data;
        if (elt_data->comm)
                strncpy(track_elt_data->comm, elt_data->comm, TASK_COMM_LEN);

        track_data->updated = true;

        return true;
}

static void save_track_data_snapshot(struct hist_trigger_data *hist_data,
                                     struct tracing_map_elt *elt, void *rec,
                                     struct ring_buffer_event *rbe, void *key,
                                     struct action_data *data,
                                     u64 *var_ref_vals)
{
        struct trace_event_file *file = hist_data->event_file;
        struct snapshot_context context;

        context.elt = elt;
        context.key = key;

        tracing_snapshot_cond(file->tr, &context);
}

static void hist_trigger_print_key(struct seq_file *m,
                                   struct hist_trigger_data *hist_data,
                                   void *key,
                                   struct tracing_map_elt *elt);

static struct action_data *snapshot_action(struct hist_trigger_data *hist_data)
{
        unsigned int i;

        if (!hist_data->n_actions)
                return NULL;

        for (i = 0; i < hist_data->n_actions; i++) {
                struct action_data *data = hist_data->actions[i];

                if (data->action == ACTION_SNAPSHOT)
                        return data;
        }

        return NULL;
}

static void track_data_snapshot_print(struct seq_file *m,
                                      struct hist_trigger_data *hist_data)
{
        struct trace_event_file *file = hist_data->event_file;
        struct track_data *track_data;
        struct action_data *action;

        track_data = tracing_cond_snapshot_data(file->tr);
        if (!track_data)
                return;

        if (!track_data->updated)
                return;

        action = snapshot_action(hist_data);
        if (!action)
                return;

        seq_puts(m, "\nSnapshot taken (see tracing/snapshot).  Details:\n");
        seq_printf(m, "\ttriggering value { %s(%s) }: %10llu",
                   action->handler == HANDLER_ONMAX ? "onmax" : "onchange",
                   action->track_data.var_str, track_data->track_val);

        seq_puts(m, "\ttriggered by event with key: ");
        hist_trigger_print_key(m, hist_data, track_data->key, &track_data->elt);
        seq_putc(m, '\n');
}
#else
static bool cond_snapshot_update(struct trace_array *tr, void *cond_data)
{
        return false;
}
static void save_track_data_snapshot(struct hist_trigger_data *hist_data,
                                     struct tracing_map_elt *elt, void *rec,
                                     struct ring_buffer_event *rbe, void *key,
                                     struct action_data *data,
                                     u64 *var_ref_vals) {}
static void track_data_snapshot_print(struct seq_file *m,
                                      struct hist_trigger_data *hist_data) {}
#endif /* CONFIG_TRACER_SNAPSHOT */

static void track_data_print(struct seq_file *m,
                             struct hist_trigger_data *hist_data,
                             struct tracing_map_elt *elt,
                             struct action_data *data)
{
        u64 track_val = get_track_val(hist_data, elt, data);
        unsigned int i, save_var_idx;

        if (data->handler == HANDLER_ONMAX)
                seq_printf(m, "\n\tmax: %10llu", track_val);
        else if (data->handler == HANDLER_ONCHANGE)
                seq_printf(m, "\n\tchanged: %10llu", track_val);

        if (data->action == ACTION_SNAPSHOT)
                return;

        for (i = 0; i < hist_data->n_save_vars; i++) {
                struct hist_field *save_val = hist_data->save_vars[i]->val;
                struct hist_field *save_var = hist_data->save_vars[i]->var;
                u64 val;

                save_var_idx = save_var->var.idx;

                val = tracing_map_read_var(elt, save_var_idx);

                if (save_val->flags & HIST_FIELD_FL_STRING) {
                        seq_printf(m, "  %s: %-32s", save_var->var.name,
                                   (char *)(uintptr_t)(val));
                } else
                        seq_printf(m, "  %s: %10llu", save_var->var.name, val);
        }
}

static void ontrack_action(struct hist_trigger_data *hist_data,
                           struct tracing_map_elt *elt, void *rec,
                           struct ring_buffer_event *rbe, void *key,
                           struct action_data *data, u64 *var_ref_vals)
{
        u64 var_val = var_ref_vals[data->track_data.var_ref->var_ref_idx];

        if (check_track_val(elt, data, var_val)) {
                save_track_val(hist_data, elt, data, var_val);
                save_track_data(hist_data, elt, rec, rbe, key, data, var_ref_vals);
        }
}

static void action_data_destroy(struct action_data *data)
{
        unsigned int i;

        lockdep_assert_held(&event_mutex);

        kfree(data->action_name);

        for (i = 0; i < data->n_params; i++)
                kfree(data->params[i]);

        if (data->synth_event)
                data->synth_event->ref--;

        kfree(data->synth_event_name);

        kfree(data);
}

static void track_data_destroy(struct hist_trigger_data *hist_data,
                               struct action_data *data)
{
        struct trace_event_file *file = hist_data->event_file;

        destroy_hist_field(data->track_data.track_var, 0);

        if (data->action == ACTION_SNAPSHOT) {
                struct track_data *track_data;

                track_data = tracing_cond_snapshot_data(file->tr);
                if (track_data && track_data->hist_data == hist_data) {
                        tracing_snapshot_cond_disable(file->tr);
                        track_data_free(track_data);
                }
        }

        kfree(data->track_data.var_str);

        action_data_destroy(data);