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         6
  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 work_struct 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 };
  68
  69 /*
  70  * Relay channel client callbacks
  71  */
  72 struct rchan_callbacks
  73 {
  74         /*
  75          * subbuf_start - called on buffer-switch to a new sub-buffer
  76          * @buf: the channel buffer containing the new sub-buffer
  77          * @subbuf: the start of the new sub-buffer
  78          * @prev_subbuf: the start of the previous sub-buffer
  79          * @prev_padding: unused space at the end of previous sub-buffer
  80          *
  81          * The client should return 1 to continue logging, 0 to stop
  82          * logging.
  83          *
  84          * NOTE: subbuf_start will also be invoked when the buffer is
  85          *       created, so that the first sub-buffer can be initialized
  86          *       if necessary.  In this case, prev_subbuf will be NULL.
  87          *
  88          * NOTE: the client can reserve bytes at the beginning of the new
  89          *       sub-buffer by calling subbuf_start_reserve() in this callback.
  90          */
  91         int (*subbuf_start) (struct rchan_buf *buf,
  92                              void *subbuf,
  93                              void *prev_subbuf,
  94                              size_t prev_padding);
  95
  96         /*
  97          * buf_mapped - relay buffer mmap notification
  98          * @buf: the channel buffer
  99          * @filp: relay file pointer
 100          *
 101          * Called when a relay file is successfully mmapped
 102          */
 103         void (*buf_mapped)(struct rchan_buf *buf,
 104                            struct file *filp);
 105
 106         /*
 107          * buf_unmapped - relay buffer unmap notification
 108          * @buf: the channel buffer
 109          * @filp: relay file pointer
 110          *
 111          * Called when a relay file is successfully unmapped
 112          */
 113         void (*buf_unmapped)(struct rchan_buf *buf,
 114                              struct file *filp);
 115         /*
 116          * create_buf_file - create file to represent a relay channel buffer
 117          * @filename: the name of the file to create
 118          * @parent: the parent of the file to create
 119          * @mode: the mode of the file to create
 120          * @buf: the channel buffer
 121          * @is_global: outparam - set non-zero if the buffer should be global
 122          *
 123          * Called during relay_open(), once for each per-cpu buffer,
 124          * to allow the client to create a file to be used to
 125          * represent the corresponding channel buffer.  If the file is
 126          * created outside of relay, the parent must also exist in
 127          * that filesystem.
 128          *
 129          * The callback should return the dentry of the file created
 130          * to represent the relay buffer.
 131          *
 132          * Setting the is_global outparam to a non-zero value will
 133          * cause relay_open() to create a single global buffer rather
 134          * than the default set of per-cpu buffers.
 135          *
 136          * See Documentation/filesystems/relayfs.txt for more info.
 137          */
 138         struct dentry *(*create_buf_file)(const char *filename,
 139                                           struct dentry *parent,
 140                                           int mode,
 141                                           struct rchan_buf *buf,
 142                                           int *is_global);
 143
 144         /*
 145          * remove_buf_file - remove file representing a relay channel buffer
 146          * @dentry: the dentry of the file to remove
 147          *
 148          * Called during relay_close(), once for each per-cpu buffer,
 149          * to allow the client to remove a file used to represent a
 150          * channel buffer.
 151          *
 152          * The callback should return 0 if successful, negative if not.
 153          */
 154         int (*remove_buf_file)(struct dentry *dentry);
 155 };
 156
 157 /*
 158  * CONFIG_RELAY kernel API, kernel/relay.c
 159  */
 160
 161 struct rchan *relay_open(const char *base_filename,
 162                          struct dentry *parent,
 163                          size_t subbuf_size,
 164                          size_t n_subbufs,
 165                          struct rchan_callbacks *cb);
 166 extern void relay_close(struct rchan *chan);
 167 extern void relay_flush(struct rchan *chan);
 168 extern void relay_subbufs_consumed(struct rchan *chan,
 169                                    unsigned int cpu,
 170                                    size_t consumed);
 171 extern void relay_reset(struct rchan *chan);
 172 extern int relay_buf_full(struct rchan_buf *buf);
 173
 174 extern size_t relay_switch_subbuf(struct rchan_buf *buf,
 175                                   size_t length);
 176
 177 /**
 178  *      relay_write - write data into the channel
 179  *      @chan: relay channel
 180  *      @data: data to be written
 181  *      @length: number of bytes to write
 182  *
 183  *      Writes data into the current cpu's channel buffer.
 184  *
 185  *      Protects the buffer by disabling interrupts.  Use this
 186  *      if you might be logging from interrupt context.  Try
 187  *      __relay_write() if you know you won't be logging from
 188  *      interrupt context.
 189  */
 190 static inline void relay_write(struct rchan *chan,
 191                                const void *data,
 192                                size_t length)
 193 {
 194         unsigned long flags;
 195         struct rchan_buf *buf;
 196
 197         local_irq_save(flags);
 198         buf = chan->buf[smp_processor_id()];
 199         if (unlikely(buf->offset + length > chan->subbuf_size))
 200                 length = relay_switch_subbuf(buf, length);
 201         memcpy(buf->data + buf->offset, data, length);
 202         buf->offset += length;
 203         local_irq_restore(flags);
 204 }
 205
 206 /**
 207  *      __relay_write - write data into the channel
 208  *      @chan: relay channel
 209  *      @data: data to be written
 210  *      @length: number of bytes to write
 211  *
 212  *      Writes data into the current cpu's channel buffer.
 213  *
 214  *      Protects the buffer by disabling preemption.  Use
 215  *      relay_write() if you might be logging from interrupt
 216  *      context.
 217  */
 218 static inline void __relay_write(struct rchan *chan,
 219                                  const void *data,
 220                                  size_t length)
 221 {
 222         struct rchan_buf *buf;
 223
 224         buf = chan->buf[get_cpu()];
 225         if (unlikely(buf->offset + length > buf->chan->subbuf_size))
 226                 length = relay_switch_subbuf(buf, length);
 227         memcpy(buf->data + buf->offset, data, length);
 228         buf->offset += length;
 229         put_cpu();
 230 }
 231
 232 /**
 233  *      relay_reserve - reserve slot in channel buffer
 234  *      @chan: relay channel
 235  *      @length: number of bytes to reserve
 236  *
 237  *      Returns pointer to reserved slot, NULL if full.
 238  *
 239  *      Reserves a slot in the current cpu's channel buffer.
 240  *      Does not protect the buffer at all - caller must provide
 241  *      appropriate synchronization.
 242  */
 243 static inline void *relay_reserve(struct rchan *chan, size_t length)
 244 {
 245         void *reserved;
 246         struct rchan_buf *buf = chan->buf[smp_processor_id()];
 247
 248         if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
 249                 length = relay_switch_subbuf(buf, length);
 250                 if (!length)
 251                         return NULL;
 252         }
 253         reserved = buf->data + buf->offset;
 254         buf->offset += length;
 255
 256         return reserved;
 257 }
 258
 259 /**
 260  *      subbuf_start_reserve - reserve bytes at the start of a sub-buffer
 261  *      @buf: relay channel buffer
 262  *      @length: number of bytes to reserve
 263  *
 264  *      Helper function used to reserve bytes at the beginning of
 265  *      a sub-buffer in the subbuf_start() callback.
 266  */
 267 static inline void subbuf_start_reserve(struct rchan_buf *buf,
 268                                         size_t length)
 269 {
 270         BUG_ON(length >= buf->chan->subbuf_size - 1);
 271         buf->offset = length;
 272 }
 273
 274 /*
 275  * exported relay file operations, kernel/relay.c
 276  */
 277 extern struct file_operations relay_file_operations;
 278
 279 #endif /* _LINUX_RELAY_H */
 280