include/linux/relayfs_fs.h

   1 /*
   2  * linux/include/linux/relayfs_fs.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  * RelayFS definitions and declarations
   8  */
   9
  10 #ifndef _LINUX_RELAYFS_FS_H
  11 #define _LINUX_RELAYFS_FS_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 /*
  23  * Tracks changes to rchan/rchan_buf structs
  24  */
  25 #define RELAYFS_CHANNEL_VERSION         6
  26
  27 /*
  28  * Per-cpu relay channel buffer
  29  */
  30 struct rchan_buf
  31 {
  32         void *start;                    /* start of channel buffer */
  33         void *data;                     /* start of current sub-buffer */
  34         size_t offset;                  /* current offset into sub-buffer */
  35         size_t subbufs_produced;        /* count of sub-buffers produced */
  36         size_t subbufs_consumed;        /* count of sub-buffers consumed */
  37         struct rchan *chan;             /* associated channel */
  38         wait_queue_head_t read_wait;    /* reader wait queue */
  39         struct work_struct wake_readers; /* reader wake-up work struct */
  40         struct dentry *dentry;          /* channel file dentry */
  41         struct kref kref;               /* channel buffer refcount */
  42         struct page **page_array;       /* array of current buffer pages */
  43         unsigned int page_count;        /* number of current buffer pages */
  44         unsigned int finalized;         /* buffer has been finalized */
  45         size_t *padding;                /* padding counts per sub-buffer */
  46         size_t prev_padding;            /* temporary variable */
  47         size_t bytes_consumed;          /* bytes consumed in cur read subbuf */
  48         unsigned int cpu;               /* this buf's cpu */
  49 } ____cacheline_aligned;
  50
  51 /*
  52  * Relay channel data structure
  53  */
  54 struct rchan
  55 {
  56         u32 version;                    /* the version of this struct */
  57         size_t subbuf_size;             /* sub-buffer size */
  58         size_t n_subbufs;               /* number of sub-buffers per buffer */
  59         size_t alloc_size;              /* total buffer size allocated */
  60         struct rchan_callbacks *cb;     /* client callbacks */
  61         struct kref kref;               /* channel refcount */
  62         void *private_data;             /* for user-defined data */
  63         size_t last_toobig;             /* tried to log event > subbuf size */
  64         struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */
  65 };
  66
  67 /*
  68  * Relay channel client callbacks
  69  */
  70 struct rchan_callbacks
  71 {
  72         /*
  73          * subbuf_start - called on buffer-switch to a new sub-buffer
  74          * @buf: the channel buffer containing the new sub-buffer
  75          * @subbuf: the start of the new sub-buffer
  76          * @prev_subbuf: the start of the previous sub-buffer
  77          * @prev_padding: unused space at the end of previous sub-buffer
  78          *
  79          * The client should return 1 to continue logging, 0 to stop
  80          * logging.
  81          *
  82          * NOTE: subbuf_start will also be invoked when the buffer is
  83          *       created, so that the first sub-buffer can be initialized
  84          *       if necessary.  In this case, prev_subbuf will be NULL.
  85          *
  86          * NOTE: the client can reserve bytes at the beginning of the new
  87          *       sub-buffer by calling subbuf_start_reserve() in this callback.
  88          */
  89         int (*subbuf_start) (struct rchan_buf *buf,
  90                              void *subbuf,
  91                              void *prev_subbuf,
  92                              size_t prev_padding);
  93
  94         /*
  95          * buf_mapped - relayfs buffer mmap notification
  96          * @buf: the channel buffer
  97          * @filp: relayfs file pointer
  98          *
  99          * Called when a relayfs file is successfully mmapped
 100          */
 101         void (*buf_mapped)(struct rchan_buf *buf,
 102                            struct file *filp);
 103
 104         /*
 105          * buf_unmapped - relayfs buffer unmap notification
 106          * @buf: the channel buffer
 107          * @filp: relayfs file pointer
 108          *
 109          * Called when a relayfs file is successfully unmapped
 110          */
 111         void (*buf_unmapped)(struct rchan_buf *buf,
 112                              struct file *filp);
 113         /*
 114          * create_buf_file - create file to represent a relayfs channel buffer
 115          * @filename: the name of the file to create
 116          * @parent: the parent of the file to create
 117          * @mode: the mode of the file to create
 118          * @buf: the channel buffer
 119          * @is_global: outparam - set non-zero if the buffer should be global
 120          *
 121          * Called during relay_open(), once for each per-cpu buffer,
 122          * to allow the client to create a file to be used to
 123          * represent the corresponding channel buffer.  If the file is
 124          * created outside of relayfs, the parent must also exist in
 125          * that filesystem.
 126          *
 127          * The callback should return the dentry of the file created
 128          * to represent the relay buffer.
 129          *
 130          * Setting the is_global outparam to a non-zero value will
 131          * cause relay_open() to create a single global buffer rather
 132          * than the default set of per-cpu buffers.
 133          *
 134          * See Documentation/filesystems/relayfs.txt for more info.
 135          */
 136         struct dentry *(*create_buf_file)(const char *filename,
 137                                           struct dentry *parent,
 138                                           int mode,
 139                                           struct rchan_buf *buf,
 140                                           int *is_global);
 141
 142         /*
 143          * remove_buf_file - remove file representing a relayfs channel buffer
 144          * @dentry: the dentry of the file to remove
 145          *
 146          * Called during relay_close(), once for each per-cpu buffer,
 147          * to allow the client to remove a file used to represent a
 148          * channel buffer.
 149          *
 150          * The callback should return 0 if successful, negative if not.
 151          */
 152         int (*remove_buf_file)(struct dentry *dentry);
 153 };
 154
 155 /*
 156  * relayfs kernel API, fs/relayfs/relay.c
 157  */
 158
 159 struct rchan *relay_open(const char *base_filename,
 160                          struct dentry *parent,
 161                          size_t subbuf_size,
 162                          size_t n_subbufs,
 163                          struct rchan_callbacks *cb);
 164 extern void relay_close(struct rchan *chan);
 165 extern void relay_flush(struct rchan *chan);
 166 extern void relay_subbufs_consumed(struct rchan *chan,
 167                                    unsigned int cpu,
 168                                    size_t consumed);
 169 extern void relay_reset(struct rchan *chan);
 170 extern int relay_buf_full(struct rchan_buf *buf);
 171
 172 extern size_t relay_switch_subbuf(struct rchan_buf *buf,
 173                                   size_t length);
 174 extern struct dentry *relayfs_create_dir(const char *name,
 175                                          struct dentry *parent);
 176 extern int relayfs_remove_dir(struct dentry *dentry);
 177 extern struct dentry *relayfs_create_file(const char *name,
 178                                           struct dentry *parent,
 179                                           int mode,
 180                                           struct file_operations *fops,
 181                                           void *data);
 182 extern int relayfs_remove_file(struct dentry *dentry);
 183
 184 /**
 185  *      relay_write - write data into the channel
 186  *      @chan: relay channel
 187  *      @data: data to be written
 188  *      @length: number of bytes to write
 189  *
 190  *      Writes data into the current cpu's channel buffer.
 191  *
 192  *      Protects the buffer by disabling interrupts.  Use this
 193  *      if you might be logging from interrupt context.  Try
 194  *      __relay_write() if you know you won't be logging from
 195  *      interrupt context.
 196  */
 197 static inline void relay_write(struct rchan *chan,
 198                                const void *data,
 199                                size_t length)
 200 {
 201         unsigned long flags;
 202         struct rchan_buf *buf;
 203
 204         local_irq_save(flags);
 205         buf = chan->buf[smp_processor_id()];
 206         if (unlikely(buf->offset + length > chan->subbuf_size))
 207                 length = relay_switch_subbuf(buf, length);
 208         memcpy(buf->data + buf->offset, data, length);
 209         buf->offset += length;
 210         local_irq_restore(flags);
 211 }
 212
 213 /**
 214  *      __relay_write - write data into the channel
 215  *      @chan: relay channel
 216  *      @data: data to be written
 217  *      @length: number of bytes to write
 218  *
 219  *      Writes data into the current cpu's channel buffer.
 220  *
 221  *      Protects the buffer by disabling preemption.  Use
 222  *      relay_write() if you might be logging from interrupt
 223  *      context.
 224  */
 225 static inline void __relay_write(struct rchan *chan,
 226                                  const void *data,
 227                                  size_t length)
 228 {
 229         struct rchan_buf *buf;
 230
 231         buf = chan->buf[get_cpu()];
 232         if (unlikely(buf->offset + length > buf->chan->subbuf_size))
 233                 length = relay_switch_subbuf(buf, length);
 234         memcpy(buf->data + buf->offset, data, length);
 235         buf->offset += length;
 236         put_cpu();
 237 }
 238
 239 /**
 240  *      relay_reserve - reserve slot in channel buffer
 241  *      @chan: relay channel
 242  *      @length: number of bytes to reserve
 243  *
 244  *      Returns pointer to reserved slot, NULL if full.
 245  *
 246  *      Reserves a slot in the current cpu's channel buffer.
 247  *      Does not protect the buffer at all - caller must provide
 248  *      appropriate synchronization.
 249  */
 250 static inline void *relay_reserve(struct rchan *chan, size_t length)
 251 {
 252         void *reserved;
 253         struct rchan_buf *buf = chan->buf[smp_processor_id()];
 254
 255         if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
 256                 length = relay_switch_subbuf(buf, length);
 257                 if (!length)
 258                         return NULL;
 259         }
 260         reserved = buf->data + buf->offset;
 261         buf->offset += length;
 262
 263         return reserved;
 264 }
 265
 266 /**
 267  *      subbuf_start_reserve - reserve bytes at the start of a sub-buffer
 268  *      @buf: relay channel buffer
 269  *      @length: number of bytes to reserve
 270  *
 271  *      Helper function used to reserve bytes at the beginning of
 272  *      a sub-buffer in the subbuf_start() callback.
 273  */
 274 static inline void subbuf_start_reserve(struct rchan_buf *buf,
 275                                         size_t length)
 276 {
 277         BUG_ON(length >= buf->chan->subbuf_size - 1);
 278         buf->offset = length;
 279 }
 280
 281 /*
 282  * exported relay file operations, fs/relayfs/inode.c
 283  */
 284 extern struct file_operations relay_file_operations;
 285
 286 #endif /* _LINUX_RELAYFS_FS_H */
 287