linux/include/linux/relay.h
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   1/*
   2 * linux/include/linux/relay.h
   3 *
   4 * Copyright (C) 2002, 2003 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
   5 * Copyright (C) 1999, 2000, 2001, 2002 - Karim Yaghmour (karim@opersys.com)
   6 *
   7 * CONFIG_RELAY definitions and declarations
   8 */
   9
  10#ifndef _LINUX_RELAY_H
  11#define _LINUX_RELAY_H
  12
  13#include <linux/types.h>
  14#include <linux/sched.h>
  15#include <linux/timer.h>
  16#include <linux/wait.h>
  17#include <linux/list.h>
  18#include <linux/bug.h>
  19#include <linux/fs.h>
  20#include <linux/poll.h>
  21#include <linux/kref.h>
  22
  23/* Needs a _much_ better name... */
  24#define FIX_SIZE(x) ((((x) - 1) & PAGE_MASK) + PAGE_SIZE)
  25
  26/*
  27 * Tracks changes to rchan/rchan_buf structs
  28 */
  29#define RELAYFS_CHANNEL_VERSION         7
  30
  31/*
  32 * Per-cpu relay channel buffer
  33 */
  34struct rchan_buf
  35{
  36        void *start;                    /* start of channel buffer */
  37        void *data;                     /* start of current sub-buffer */
  38        size_t offset;                  /* current offset into sub-buffer */
  39        size_t subbufs_produced;        /* count of sub-buffers produced */
  40        size_t subbufs_consumed;        /* count of sub-buffers consumed */
  41        struct rchan *chan;             /* associated channel */
  42        wait_queue_head_t read_wait;    /* reader wait queue */
  43        struct timer_list timer;        /* reader wake-up timer */
  44        struct dentry *dentry;          /* channel file dentry */
  45        struct kref kref;               /* channel buffer refcount */
  46        struct page **page_array;       /* array of current buffer pages */
  47        unsigned int page_count;        /* number of current buffer pages */
  48        unsigned int finalized;         /* buffer has been finalized */
  49        size_t *padding;                /* padding counts per sub-buffer */
  50        size_t prev_padding;            /* temporary variable */
  51        size_t bytes_consumed;          /* bytes consumed in cur read subbuf */
  52        size_t early_bytes;             /* bytes consumed before VFS inited */
  53        unsigned int cpu;               /* this buf's cpu */
  54} ____cacheline_aligned;
  55
  56/*
  57 * Relay channel data structure
  58 */
  59struct rchan
  60{
  61        u32 version;                    /* the version of this struct */
  62        size_t subbuf_size;             /* sub-buffer size */
  63        size_t n_subbufs;               /* number of sub-buffers per buffer */
  64        size_t alloc_size;              /* total buffer size allocated */
  65        struct rchan_callbacks *cb;     /* client callbacks */
  66        struct kref kref;               /* channel refcount */
  67        void *private_data;             /* for user-defined data */
  68        size_t last_toobig;             /* tried to log event > subbuf size */
  69        struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */
  70        int is_global;                  /* One global buffer ? */
  71        struct list_head list;          /* for channel list */
  72        struct dentry *parent;          /* parent dentry passed to open */
  73        int has_base_filename;          /* has a filename associated? */
  74        char base_filename[NAME_MAX];   /* saved base filename */
  75};
  76
  77/*
  78 * Relay channel client callbacks
  79 */
  80struct rchan_callbacks
  81{
  82        /*
  83         * subbuf_start - called on buffer-switch to a new sub-buffer
  84         * @buf: the channel buffer containing the new sub-buffer
  85         * @subbuf: the start of the new sub-buffer
  86         * @prev_subbuf: the start of the previous sub-buffer
  87         * @prev_padding: unused space at the end of previous sub-buffer
  88         *
  89         * The client should return 1 to continue logging, 0 to stop
  90         * logging.
  91         *
  92         * NOTE: subbuf_start will also be invoked when the buffer is
  93         *       created, so that the first sub-buffer can be initialized
  94         *       if necessary.  In this case, prev_subbuf will be NULL.
  95         *
  96         * NOTE: the client can reserve bytes at the beginning of the new
  97         *       sub-buffer by calling subbuf_start_reserve() in this callback.
  98         */
  99        int (*subbuf_start) (struct rchan_buf *buf,
 100                             void *subbuf,
 101                             void *prev_subbuf,
 102                             size_t prev_padding);
 103
 104        /*
 105         * buf_mapped - relay buffer mmap notification
 106         * @buf: the channel buffer
 107         * @filp: relay file pointer
 108         *
 109         * Called when a relay file is successfully mmapped
 110         */
 111        void (*buf_mapped)(struct rchan_buf *buf,
 112                           struct file *filp);
 113
 114        /*
 115         * buf_unmapped - relay buffer unmap notification
 116         * @buf: the channel buffer
 117         * @filp: relay file pointer
 118         *
 119         * Called when a relay file is successfully unmapped
 120         */
 121        void (*buf_unmapped)(struct rchan_buf *buf,
 122                             struct file *filp);
 123        /*
 124         * create_buf_file - create file to represent a relay channel buffer
 125         * @filename: the name of the file to create
 126         * @parent: the parent of the file to create
 127         * @mode: the mode of the file to create
 128         * @buf: the channel buffer
 129         * @is_global: outparam - set non-zero if the buffer should be global
 130         *
 131         * Called during relay_open(), once for each per-cpu buffer,
 132         * to allow the client to create a file to be used to
 133         * represent the corresponding channel buffer.  If the file is
 134         * created outside of relay, the parent must also exist in
 135         * that filesystem.
 136         *
 137         * The callback should return the dentry of the file created
 138         * to represent the relay buffer.
 139         *
 140         * Setting the is_global outparam to a non-zero value will
 141         * cause relay_open() to create a single global buffer rather
 142         * than the default set of per-cpu buffers.
 143         *
 144         * See Documentation/filesystems/relay.txt for more info.
 145         */
 146        struct dentry *(*create_buf_file)(const char *filename,
 147                                          struct dentry *parent,
 148                                          umode_t mode,
 149                                          struct rchan_buf *buf,
 150                                          int *is_global);
 151
 152        /*
 153         * remove_buf_file - remove file representing a relay channel buffer
 154         * @dentry: the dentry of the file to remove
 155         *
 156         * Called during relay_close(), once for each per-cpu buffer,
 157         * to allow the client to remove a file used to represent a
 158         * channel buffer.
 159         *
 160         * The callback should return 0 if successful, negative if not.
 161         */
 162        int (*remove_buf_file)(struct dentry *dentry);
 163};
 164
 165/*
 166 * CONFIG_RELAY kernel API, kernel/relay.c
 167 */
 168
 169struct rchan *relay_open(const char *base_filename,
 170                         struct dentry *parent,
 171                         size_t subbuf_size,
 172                         size_t n_subbufs,
 173                         struct rchan_callbacks *cb,
 174                         void *private_data);
 175extern int relay_late_setup_files(struct rchan *chan,
 176                                  const char *base_filename,
 177                                  struct dentry *parent);
 178extern void relay_close(struct rchan *chan);
 179extern void relay_flush(struct rchan *chan);
 180extern void relay_subbufs_consumed(struct rchan *chan,
 181                                   unsigned int cpu,
 182                                   size_t consumed);
 183extern void relay_reset(struct rchan *chan);
 184extern int relay_buf_full(struct rchan_buf *buf);
 185
 186extern size_t relay_switch_subbuf(struct rchan_buf *buf,
 187                                  size_t length);
 188
 189/**
 190 *      relay_write - write data into the channel
 191 *      @chan: relay channel
 192 *      @data: data to be written
 193 *      @length: number of bytes to write
 194 *
 195 *      Writes data into the current cpu's channel buffer.
 196 *
 197 *      Protects the buffer by disabling interrupts.  Use this
 198 *      if you might be logging from interrupt context.  Try
 199 *      __relay_write() if you know you won't be logging from
 200 *      interrupt context.
 201 */
 202static inline void relay_write(struct rchan *chan,
 203                               const void *data,
 204                               size_t length)
 205{
 206        unsigned long flags;
 207        struct rchan_buf *buf;
 208
 209        local_irq_save(flags);
 210        buf = chan->buf[smp_processor_id()];
 211        if (unlikely(buf->offset + length > chan->subbuf_size))
 212                length = relay_switch_subbuf(buf, length);
 213        memcpy(buf->data + buf->offset, data, length);
 214        buf->offset += length;
 215        local_irq_restore(flags);
 216}
 217
 218/**
 219 *      __relay_write - write data into the channel
 220 *      @chan: relay channel
 221 *      @data: data to be written
 222 *      @length: number of bytes to write
 223 *
 224 *      Writes data into the current cpu's channel buffer.
 225 *
 226 *      Protects the buffer by disabling preemption.  Use
 227 *      relay_write() if you might be logging from interrupt
 228 *      context.
 229 */
 230static inline void __relay_write(struct rchan *chan,
 231                                 const void *data,
 232                                 size_t length)
 233{
 234        struct rchan_buf *buf;
 235
 236        buf = chan->buf[get_cpu()];
 237        if (unlikely(buf->offset + length > buf->chan->subbuf_size))
 238                length = relay_switch_subbuf(buf, length);
 239        memcpy(buf->data + buf->offset, data, length);
 240        buf->offset += length;
 241        put_cpu();
 242}
 243
 244/**
 245 *      relay_reserve - reserve slot in channel buffer
 246 *      @chan: relay channel
 247 *      @length: number of bytes to reserve
 248 *
 249 *      Returns pointer to reserved slot, NULL if full.
 250 *
 251 *      Reserves a slot in the current cpu's channel buffer.
 252 *      Does not protect the buffer at all - caller must provide
 253 *      appropriate synchronization.
 254 */
 255static inline void *relay_reserve(struct rchan *chan, size_t length)
 256{
 257        void *reserved;
 258        struct rchan_buf *buf = chan->buf[smp_processor_id()];
 259
 260        if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
 261                length = relay_switch_subbuf(buf, length);
 262                if (!length)
 263                        return NULL;
 264        }
 265        reserved = buf->data + buf->offset;
 266        buf->offset += length;
 267
 268        return reserved;
 269}
 270
 271/**
 272 *      subbuf_start_reserve - reserve bytes at the start of a sub-buffer
 273 *      @buf: relay channel buffer
 274 *      @length: number of bytes to reserve
 275 *
 276 *      Helper function used to reserve bytes at the beginning of
 277 *      a sub-buffer in the subbuf_start() callback.
 278 */
 279static inline void subbuf_start_reserve(struct rchan_buf *buf,
 280                                        size_t length)
 281{
 282        BUG_ON(length >= buf->chan->subbuf_size - 1);
 283        buf->offset = length;
 284}
 285
 286/*
 287 * exported relay file operations, kernel/relay.c
 288 */
 289extern const struct file_operations relay_file_operations;
 290
 291#endif /* _LINUX_RELAY_H */
 292
 293
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