LXR linux/include/linux/pid.h

   1/* SPDX-License-Identifier: GPL-2.0 */
   2#ifndef _LINUX_PID_H
   3#define _LINUX_PID_H
   4
   5#include <linux/rculist.h>
   6
   7enum pid_type
   8{
   9        PIDTYPE_PID,
  10        PIDTYPE_PGID,
  11        PIDTYPE_SID,
  12#ifndef __GENKSYMS__
  13        PIDTYPE_TGID,
  14#endif
  15        PIDTYPE_MAX,
  16#ifdef __GENKSYMS__
  17        __PIDTYPE_TGID
  18#endif
  19};
  20
  21/*
  22 * What is struct pid?
  23 *
  24 * A struct pid is the kernel's internal notion of a process identifier.
  25 * It refers to individual tasks, process groups, and sessions.  While
  26 * there are processes attached to it the struct pid lives in a hash
  27 * table, so it and then the processes that it refers to can be found
  28 * quickly from the numeric pid value.  The attached processes may be
  29 * quickly accessed by following pointers from struct pid.
  30 *
  31 * Storing pid_t values in the kernel and referring to them later has a
  32 * problem.  The process originally with that pid may have exited and the
  33 * pid allocator wrapped, and another process could have come along
  34 * and been assigned that pid.
  35 *
  36 * Referring to user space processes by holding a reference to struct
  37 * task_struct has a problem.  When the user space process exits
  38 * the now useless task_struct is still kept.  A task_struct plus a
  39 * stack consumes around 10K of low kernel memory.  More precisely
  40 * this is THREAD_SIZE + sizeof(struct task_struct).  By comparison
  41 * a struct pid is about 64 bytes.
  42 *
  43 * Holding a reference to struct pid solves both of these problems.
  44 * It is small so holding a reference does not consume a lot of
  45 * resources, and since a new struct pid is allocated when the numeric pid
  46 * value is reused (when pids wrap around) we don't mistakenly refer to new
  47 * processes.
  48 */
  49
  50
  51/*
  52 * struct upid is used to get the id of the struct pid, as it is
  53 * seen in particular namespace. Later the struct pid is found with
  54 * find_pid_ns() using the int nr and struct pid_namespace *ns.
  55 */
  56
  57struct upid {
  58        int nr;
  59        struct pid_namespace *ns;
  60};
  61
  62struct pid
  63{
  64        atomic_t count;
  65        unsigned int level;
  66        /* lists of tasks that use this pid */
  67        struct hlist_head tasks[PIDTYPE_MAX];
  68        struct rcu_head rcu;
  69        struct upid numbers[1];
  70};
  71
  72extern struct pid init_struct_pid;
  73
  74struct pid_link
  75{
  76        struct hlist_node node;
  77        struct pid *pid;
  78};
  79
  80static inline struct pid *get_pid(struct pid *pid)
  81{
  82        if (pid)
  83                atomic_inc(&pid->count);
  84        return pid;
  85}
  86
  87extern void put_pid(struct pid *pid);
  88extern struct task_struct *pid_task(struct pid *pid, enum pid_type);
  89extern struct task_struct *get_pid_task(struct pid *pid, enum pid_type);
  90
  91extern struct pid *get_task_pid(struct task_struct *task, enum pid_type type);
  92
  93/*
  94 * these helpers must be called with the tasklist_lock write-held.
  95 */
  96extern void attach_pid(struct task_struct *task, enum pid_type);
  97extern void detach_pid(struct task_struct *task, enum pid_type);
  98extern void change_pid(struct task_struct *task, enum pid_type,
  99                        struct pid *pid);
 100extern void transfer_pid(struct task_struct *old, struct task_struct *new,
 101                         enum pid_type);
 102
 103struct pid_namespace;
 104extern struct pid_namespace init_pid_ns;
 105
 106/*
 107 * look up a PID in the hash table. Must be called with the tasklist_lock
 108 * or rcu_read_lock() held.
 109 *
 110 * find_pid_ns() finds the pid in the namespace specified
 111 * find_vpid() finds the pid by its virtual id, i.e. in the current namespace
 112 *
 113 * see also find_task_by_vpid() set in include/linux/sched.h
 114 */
 115extern struct pid *find_pid_ns(int nr, struct pid_namespace *ns);
 116extern struct pid *find_vpid(int nr);
 117
 118/*
 119 * Lookup a PID in the hash table, and return with it's count elevated.
 120 */
 121extern struct pid *find_get_pid(int nr);
 122extern struct pid *find_ge_pid(int nr, struct pid_namespace *);
 123int next_pidmap(struct pid_namespace *pid_ns, unsigned int last);
 124
 125extern struct pid *alloc_pid(struct pid_namespace *ns);
 126extern void free_pid(struct pid *pid);
 127extern void disable_pid_allocation(struct pid_namespace *ns);
 128
 129/*
 130 * ns_of_pid() returns the pid namespace in which the specified pid was
 131 * allocated.
 132 *
 133 * NOTE:
 134 *      ns_of_pid() is expected to be called for a process (task) that has
 135 *      an attached 'struct pid' (see attach_pid(), detach_pid()) i.e @pid
 136 *      is expected to be non-NULL. If @pid is NULL, caller should handle
 137 *      the resulting NULL pid-ns.
 138 */
 139static inline struct pid_namespace *ns_of_pid(struct pid *pid)
 140{
 141        struct pid_namespace *ns = NULL;
 142        if (pid)
 143                ns = pid->numbers[pid->level].ns;
 144        return ns;
 145}
 146
 147/*
 148 * is_child_reaper returns true if the pid is the init process
 149 * of the current namespace. As this one could be checked before
 150 * pid_ns->child_reaper is assigned in copy_process, we check
 151 * with the pid number.
 152 */
 153static inline bool is_child_reaper(struct pid *pid)
 154{
 155        return pid->numbers[pid->level].nr == 1;
 156}
 157
 158/*
 159 * the helpers to get the pid's id seen from different namespaces
 160 *
 161 * pid_nr()    : global id, i.e. the id seen from the init namespace;
 162 * pid_vnr()   : virtual id, i.e. the id seen from the pid namespace of
 163 *               current.
 164 * pid_nr_ns() : id seen from the ns specified.
 165 *
 166 * see also task_xid_nr() etc in include/linux/sched.h
 167 */
 168
 169static inline pid_t pid_nr(struct pid *pid)
 170{
 171        pid_t nr = 0;
 172        if (pid)
 173                nr = pid->numbers[0].nr;
 174        return nr;
 175}
 176
 177pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
 178pid_t pid_vnr(struct pid *pid);
 179
 180#define do_each_pid_task(pid, type, task)                               \
 181        do {                                                            \
 182                if ((pid) != NULL)                                      \
 183                        hlist_for_each_entry_rcu((task),                \
 184                                &(pid)->tasks[type], pid_links[type]) {
 185
 186                        /*
 187                         * Both old and new leaders may be attached to
 188                         * the same pid in the middle of de_thread().
 189                         */
 190#define while_each_pid_task(pid, type, task)                            \
 191                                if (type == PIDTYPE_PID)                \
 192                                        break;                          \
 193                        }                                               \
 194        } while (0)
 195
 196#define do_each_pid_thread(pid, type, task)                             \
 197        do_each_pid_task(pid, type, task) {                             \
 198                struct task_struct *tg___ = task;                       \
 199                for_each_thread(tg___, task) {
 200
 201#define while_each_pid_thread(pid, type, task)                          \
 202                }                                                       \
 203                task = tg___;                                           \
 204        } while_each_pid_task(pid, type, task)
 205#endif /* _LINUX_PID_H */
 206