/* SPDX-License-Identifier: GPL-2.0 */
/*
 * linux/include/linux/relay.h
 *
 * Copyright (C) 2002, 2003 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
 * Copyright (C) 1999, 2000, 2001, 2002 - Karim Yaghmour (karim@opersys.com)
 *
 * CONFIG_RELAY definitions and declarations
 */

#ifndef _LINUX_RELAY_H
#define _LINUX_RELAY_H

#include <linux/types.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/wait.h>
#include <linux/list.h>
#include <linux/irq_work.h>
#include <linux/bug.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/kref.h>
#include <linux/percpu.h>

/*
 * Tracks changes to rchan/rchan_buf structs
 */
#define RELAYFS_CHANNEL_VERSION         7

/*
 * Per-cpu relay channel buffer
 */
struct rchan_buf
{
        void *start;                    /* start of channel buffer */
        void *data;                     /* start of current sub-buffer */
        size_t offset;                  /* current offset into sub-buffer */
        size_t subbufs_produced;        /* count of sub-buffers produced */
        size_t subbufs_consumed;        /* count of sub-buffers consumed */
        struct rchan *chan;             /* associated channel */
        wait_queue_head_t read_wait;    /* reader wait queue */
        struct irq_work wakeup_work;    /* reader wakeup */
        struct dentry *dentry;          /* channel file dentry */
        struct kref kref;               /* channel buffer refcount */
        struct page **page_array;       /* array of current buffer pages */
        unsigned int page_count;        /* number of current buffer pages */
        unsigned int finalized;         /* buffer has been finalized */
        size_t *padding;                /* padding counts per sub-buffer */
        size_t prev_padding;            /* temporary variable */
        size_t bytes_consumed;          /* bytes consumed in cur read subbuf */
        size_t early_bytes;             /* bytes consumed before VFS inited */
        unsigned int cpu;               /* this buf's cpu */
} ____cacheline_aligned;

/*
 * Relay channel data structure
 */
struct rchan
{
        u32 version;                    /* the version of this struct */
        size_t subbuf_size;             /* sub-buffer size */
        size_t n_subbufs;               /* number of sub-buffers per buffer */
        size_t alloc_size;              /* total buffer size allocated */
        const struct rchan_callbacks *cb; /* client callbacks */
        struct kref kref;               /* channel refcount */
        void *private_data;             /* for user-defined data */
        size_t last_toobig;             /* tried to log event > subbuf size */
        struct rchan_buf * __percpu *buf; /* per-cpu channel buffers */
        int is_global;                  /* One global buffer ? */
        struct list_head list;          /* for channel list */
        struct dentry *parent;          /* parent dentry passed to open */
        int has_base_filename;          /* has a filename associated? */
        char base_filename[NAME_MAX];   /* saved base filename */
};

/*
 * Relay channel client callbacks
 */
struct rchan_callbacks
{
        /*
         * subbuf_start - called on buffer-switch to a new sub-buffer
         * @buf: the channel buffer containing the new sub-buffer
         * @subbuf: the start of the new sub-buffer
         * @prev_subbuf: the start of the previous sub-buffer
         * @prev_padding: unused space at the end of previous sub-buffer
         *
         * The client should return 1 to continue logging, 0 to stop
         * logging.
         *
         * This callback is optional.
         *
         * NOTE: subbuf_start will also be invoked when the buffer is
         *       created, so that the first sub-buffer can be initialized
         *       if necessary.  In this case, prev_subbuf will be NULL.
         *
         * NOTE: the client can reserve bytes at the beginning of the new
         *       sub-buffer by calling subbuf_start_reserve() in this callback.
         */
        int (*subbuf_start) (struct rchan_buf *buf,
                             void *subbuf,
                             void *prev_subbuf,
                             size_t prev_padding);

        /*
         * create_buf_file - create file to represent a relay channel buffer
         * @filename: the name of the file to create
         * @parent: the parent of the file to create
         * @mode: the mode of the file to create
         * @buf: the channel buffer
         * @is_global: outparam - set non-zero if the buffer should be global
         *
         * Called during relay_open(), once for each per-cpu buffer,
         * to allow the client to create a file to be used to
         * represent the corresponding channel buffer.  If the file is
         * created outside of relay, the parent must also exist in
         * that filesystem.
         *
         * The callback should return the dentry of the file created
         * to represent the relay buffer.
         *
         * Setting the is_global outparam to a non-zero value will
         * cause relay_open() to create a single global buffer rather
         * than the default set of per-cpu buffers.
         *
         * This callback is mandatory.
         *
         * See Documentation/filesystems/relay.rst for more info.
         */
        struct dentry *(*create_buf_file)(const char *filename,
                                          struct dentry *parent,
                                          umode_t mode,
                                          struct rchan_buf *buf,
                                          int *is_global);

        /*
         * remove_buf_file - remove file representing a relay channel buffer
         * @dentry: the dentry of the file to remove
         *
         * Called during relay_close(), once for each per-cpu buffer,
         * to allow the client to remove a file used to represent a
         * channel buffer.
         *
         * The callback should return 0 if successful, negative if not.
         *
         * This callback is mandatory.
         */
        int (*remove_buf_file)(struct dentry *dentry);
};

/*
 * CONFIG_RELAY kernel API, kernel/relay.c
 */

struct rchan *relay_open(const char *base_filename,
                         struct dentry *parent,
                         size_t subbuf_size,
                         size_t n_subbufs,
                         const struct rchan_callbacks *cb,
                         void *private_data);
extern int relay_late_setup_files(struct rchan *chan,
                                  const char *base_filename,
                                  struct dentry *parent);
extern void relay_close(struct rchan *chan);
extern void relay_flush(struct rchan *chan);
extern void relay_subbufs_consumed(struct rchan *chan,
                                   unsigned int cpu,
                                   size_t consumed);
extern void relay_reset(struct rchan *chan);
extern int relay_buf_full(struct rchan_buf *buf);

extern size_t relay_switch_subbuf(struct rchan_buf *buf,
                                  size_t length);

/**
 *      relay_write - write data into the channel
 *      @chan: relay channel
 *      @data: data to be written
 *      @length: number of bytes to write
 *
 *      Writes data into the current cpu's channel buffer.
 *
 *      Protects the buffer by disabling interrupts.  Use this
 *      if you might be logging from interrupt context.  Try
 *      __relay_write() if you know you won't be logging from
 *      interrupt context.
 */
static inline void relay_write(struct rchan *chan,
                               const void *data,
                               size_t length)
{
        unsigned long flags;
        struct rchan_buf *buf;

        local_irq_save(flags);
        buf = *this_cpu_ptr(chan->buf);
        if (unlikely(buf->offset + length > chan->subbuf_size))
                length = relay_switch_subbuf(buf, length);
        memcpy(buf->data + buf->offset, data, length);
        buf->offset += length;
        local_irq_restore(flags);
}

/**
 *      __relay_write - write data into the channel
 *      @chan: relay channel
 *      @data: data to be written
 *      @length: number of bytes to write
 *
 *      Writes data into the current cpu's channel buffer.
 *
 *      Protects the buffer by disabling preemption.  Use
 *      relay_write() if you might be logging from interrupt
 *      context.
 */
static inline void __relay_write(struct rchan *chan,
                                 const void *data,
                                 size_t length)
{
        struct rchan_buf *buf;

        buf = *get_cpu_ptr(chan->buf);
        if (unlikely(buf->offset + length > buf->chan->subbuf_size))
                length = relay_switch_subbuf(buf, length);
        memcpy(buf->data + buf->offset, data, length);
        buf->offset += length;
        put_cpu_ptr(chan->buf);
}

/**
 *      relay_reserve - reserve slot in channel buffer
 *      @chan: relay channel
 *      @length: number of bytes to reserve
 *
 *      Returns pointer to reserved slot, NULL if full.
 *
 *      Reserves a slot in the current cpu's channel buffer.
 *      Does not protect the buffer at all - caller must provide
 *      appropriate synchronization.
 */
static inline void *relay_reserve(struct rchan *chan, size_t length)
{
        void *reserved = NULL;
        struct rchan_buf *buf = *get_cpu_ptr(chan->buf);

        if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
                length = relay_switch_subbuf(buf, length);
                if (!length)
                        goto end;
        }
        reserved = buf->data + buf->offset;
        buf->offset += length;

end:
        put_cpu_ptr(chan->buf);
        return reserved;
}

/**
 *      subbuf_start_reserve - reserve bytes at the start of a sub-buffer
 *      @buf: relay channel buffer
 *      @length: number of bytes to reserve
 *
 *      Helper function used to reserve bytes at the beginning of
 *      a sub-buffer in the subbuf_start() callback.
 */
static inline void subbuf_start_reserve(struct rchan_buf *buf,
                                        size_t length)
{
        BUG_ON(length >= buf->chan->subbuf_size - 1);
        buf->offset = length;
}

/*
 * exported relay file operations, kernel/relay.c
 */
extern const struct file_operations relay_file_operations;

#ifdef CONFIG_RELAY
int relay_prepare_cpu(unsigned int cpu);
#else
#define relay_prepare_cpu     NULL
#endif

#endif /* _LINUX_RELAY_H */