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