relay.h

Go to the documentation of this file.

/*
 * linux/include/linux/relay.h
 *
 * Copyright (C) 2002, 2003 - Tom Zanussi ([email protected]), IBM Corp
 * Copyright (C) 1999, 2000, 2001, 2002 - Karim Yaghmour ([email protected])
 *
 * 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/bug.h>
#include <linux/fs.h>
#include <linux/poll.h>
#include <linux/kref.h>

/* Needs a _much_ better name... */
#define FIX_SIZE(x) ((((x) - 1) & PAGE_MASK) + PAGE_SIZE)

/*
 * 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 timer_list timer;    /* reader wake-up timer */
    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 */
    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 *buf[NR_CPUS]; /* 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.
     *
     * 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);

    /*
     * buf_mapped - relay buffer mmap notification
     * @buf: the channel buffer
     * @filp: relay file pointer
     *
     * Called when a relay file is successfully mmapped
     */
        void (*buf_mapped)(struct rchan_buf *buf,
               struct file *filp);

    /*
     * buf_unmapped - relay buffer unmap notification
     * @buf: the channel buffer
     * @filp: relay file pointer
     *
     * Called when a relay file is successfully unmapped
     */
        void (*buf_unmapped)(struct rchan_buf *buf,
                 struct file *filp);
    /*
     * 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.
     *
     * See Documentation/filesystems/relay.txt 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.
     */
    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,
             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);

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 = chan->buf[smp_processor_id()];
    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);
}

static inline void __relay_write(struct rchan *chan,
                 const void *data,
                 size_t length)
{
    struct rchan_buf *buf;

    buf = chan->buf[get_cpu()];
    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();
}

static inline void *relay_reserve(struct rchan *chan, size_t length)
{
    void *reserved;
    struct rchan_buf *buf = chan->buf[smp_processor_id()];

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

    return reserved;
}

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;

#endif /* _LINUX_RELAY_H */