include/linux/relay.h

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