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