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