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/percpu.h>
  23 #include <linux/irq_work.h>
  24
  25 /*
  26  * Tracks changes to rchan/rchan_buf structs
  27  */
  28 #define RELAYFS_CHANNEL_VERSION         7
  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 irq_work wakeup_work;    /* reader wakeup */
  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         size_t early_bytes;             /* bytes consumed before VFS inited */
  52         unsigned int cpu;               /* this buf's cpu */
  53 } ____cacheline_aligned;
  54
  55 /*
  56  * Relay channel data structure
  57  */
  58 struct rchan
  59 {
  60         u32 version;                    /* the version of this struct */
  61         size_t subbuf_size;             /* sub-buffer size */
  62         size_t n_subbufs;               /* number of sub-buffers per buffer */
  63         size_t alloc_size;              /* total buffer size allocated */
  64         struct rchan_callbacks *cb;     /* client callbacks */
  65         struct kref kref;               /* channel refcount */
  66         void *private_data;             /* for user-defined data */
  67         size_t last_toobig;             /* tried to log event > subbuf size */
  68         struct rchan_buf ** __percpu buf; /* per-cpu channel buffers */
  69         int is_global;                  /* One global buffer ? */
  70         struct list_head list;          /* for channel list */
  71         struct dentry *parent;          /* parent dentry passed to open */
  72         int has_base_filename;          /* has a filename associated? */
  73         char base_filename[NAME_MAX];   /* saved base filename */
  74 };
  75
  76 /*
  77  * Relay channel client callbacks
  78  */
  79 struct rchan_callbacks
  80 {
  81         /*
  82          * subbuf_start - called on buffer-switch to a new sub-buffer
  83          * @buf: the channel buffer containing the new sub-buffer
  84          * @subbuf: the start of the new sub-buffer
  85          * @prev_subbuf: the start of the previous sub-buffer
  86          * @prev_padding: unused space at the end of previous sub-buffer
  87          *
  88          * The client should return 1 to continue logging, 0 to stop
  89          * logging.
  90          *
  91          * NOTE: subbuf_start will also be invoked when the buffer is
  92          *       created, so that the first sub-buffer can be initialized
  93          *       if necessary.  In this case, prev_subbuf will be NULL.
  94          *
  95          * NOTE: the client can reserve bytes at the beginning of the new
  96          *       sub-buffer by calling subbuf_start_reserve() in this callback.
  97          */
  98         int (*subbuf_start) (struct rchan_buf *buf,
  99                              void *subbuf,
 100                              void *prev_subbuf,
 101                              size_t prev_padding);
 102
 103         /*
 104          * buf_mapped - relay buffer mmap notification
 105          * @buf: the channel buffer
 106          * @filp: relay file pointer
 107          *
 108          * Called when a relay file is successfully mmapped
 109          */
 110         void (*buf_mapped)(struct rchan_buf *buf,
 111                            struct file *filp);
 112
 113         /*
 114          * buf_unmapped - relay buffer unmap notification
 115          * @buf: the channel buffer
 116          * @filp: relay file pointer
 117          *
 118          * Called when a relay file is successfully unmapped
 119          */
 120         void (*buf_unmapped)(struct rchan_buf *buf,
 121                              struct file *filp);
 122         /*
 123          * create_buf_file - create file to represent a relay channel buffer
 124          * @filename: the name of the file to create
 125          * @parent: the parent of the file to create
 126          * @mode: the mode of the file to create
 127          * @buf: the channel buffer
 128          * @is_global: outparam - set non-zero if the buffer should be global
 129          *
 130          * Called during relay_open(), once for each per-cpu buffer,
 131          * to allow the client to create a file to be used to
 132          * represent the corresponding channel buffer.  If the file is
 133          * created outside of relay, the parent must also exist in
 134          * that filesystem.
 135          *
 136          * The callback should return the dentry of the file created
 137          * to represent the relay buffer.
 138          *
 139          * Setting the is_global outparam to a non-zero value will
 140          * cause relay_open() to create a single global buffer rather
 141          * than the default set of per-cpu buffers.
 142          *
 143          * See Documentation/filesystems/relay.txt for more info.
 144          */
 145         struct dentry *(*create_buf_file)(const char *filename,
 146                                           struct dentry *parent,
 147                                           umode_t mode,
 148                                           struct rchan_buf *buf,
 149                                           int *is_global);
 150
 151         /*
 152          * remove_buf_file - remove file representing a relay channel buffer
 153          * @dentry: the dentry of the file to remove
 154          *
 155          * Called during relay_close(), once for each per-cpu buffer,
 156          * to allow the client to remove a file used to represent a
 157          * channel buffer.
 158          *
 159          * The callback should return 0 if successful, negative if not.
 160          */
 161         int (*remove_buf_file)(struct dentry *dentry);
 162 };
 163
 164 /*
 165  * CONFIG_RELAY kernel API, kernel/relay.c
 166  */
 167
 168 struct rchan *relay_open(const char *base_filename,
 169                          struct dentry *parent,
 170                          size_t subbuf_size,
 171                          size_t n_subbufs,
 172                          struct rchan_callbacks *cb,
 173                          void *private_data);
 174 extern int relay_late_setup_files(struct rchan *chan,
 175                                   const char *base_filename,
 176                                   struct dentry *parent);
 177 extern void relay_close(struct rchan *chan);
 178 extern void relay_flush(struct rchan *chan);
 179 extern void relay_subbufs_consumed(struct rchan *chan,
 180                                    unsigned int cpu,
 181                                    size_t consumed);
 182 extern void relay_reset(struct rchan *chan);
 183 extern int relay_buf_full(struct rchan_buf *buf);
 184
 185 extern size_t relay_switch_subbuf(struct rchan_buf *buf,
 186                                   size_t length);
 187
 188 /**
 189  *      relay_write - write data into the channel
 190  *      @chan: relay channel
 191  *      @data: data to be written
 192  *      @length: number of bytes to write
 193  *
 194  *      Writes data into the current cpu's channel buffer.
 195  *
 196  *      Protects the buffer by disabling interrupts.  Use this
 197  *      if you might be logging from interrupt context.  Try
 198  *      __relay_write() if you know you won't be logging from
 199  *      interrupt context.
 200  */
 201 static inline void relay_write(struct rchan *chan,
 202                                const void *data,
 203                                size_t length)
 204 {
 205         unsigned long flags;
 206         struct rchan_buf *buf;
 207
 208         local_irq_save(flags);
 209         buf = *this_cpu_ptr(chan->buf);
 210         if (unlikely(buf->offset + length > chan->subbuf_size))
 211                 length = relay_switch_subbuf(buf, length);
 212         memcpy(buf->data + buf->offset, data, length);
 213         buf->offset += length;
 214         local_irq_restore(flags);
 215 }
 216
 217 /**
 218  *      __relay_write - write data into the channel
 219  *      @chan: relay channel
 220  *      @data: data to be written
 221  *      @length: number of bytes to write
 222  *
 223  *      Writes data into the current cpu's channel buffer.
 224  *
 225  *      Protects the buffer by disabling preemption.  Use
 226  *      relay_write() if you might be logging from interrupt
 227  *      context.
 228  */
 229 static inline void __relay_write(struct rchan *chan,
 230                                  const void *data,
 231                                  size_t length)
 232 {
 233         struct rchan_buf *buf;
 234
 235         buf = *get_cpu_ptr(chan->buf);
 236         if (unlikely(buf->offset + length > buf->chan->subbuf_size))
 237                 length = relay_switch_subbuf(buf, length);
 238         memcpy(buf->data + buf->offset, data, length);
 239         buf->offset += length;
 240         put_cpu_ptr(chan->buf);
 241 }
 242
 243 /**
 244  *      relay_reserve - reserve slot in channel buffer
 245  *      @chan: relay channel
 246  *      @length: number of bytes to reserve
 247  *
 248  *      Returns pointer to reserved slot, NULL if full.
 249  *
 250  *      Reserves a slot in the current cpu's channel buffer.
 251  *      Does not protect the buffer at all - caller must provide
 252  *      appropriate synchronization.
 253  */
 254 static inline void *relay_reserve(struct rchan *chan, size_t length)
 255 {
 256         void *reserved = NULL;
 257         struct rchan_buf *buf = *get_cpu_ptr(chan->buf);
 258
 259         if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
 260                 length = relay_switch_subbuf(buf, length);
 261                 if (!length)
 262                         goto end;
 263         }
 264         reserved = buf->data + buf->offset;
 265         buf->offset += length;
 266
 267 end:
 268         put_cpu_ptr(chan->buf);
 269         return reserved;
 270 }
 271
 272 /**
 273  *      subbuf_start_reserve - reserve bytes at the start of a sub-buffer
 274  *      @buf: relay channel buffer
 275  *      @length: number of bytes to reserve
 276  *
 277  *      Helper function used to reserve bytes at the beginning of
 278  *      a sub-buffer in the subbuf_start() callback.
 279  */
 280 static inline void subbuf_start_reserve(struct rchan_buf *buf,
 281                                         size_t length)
 282 {
 283         BUG_ON(length >= buf->chan->subbuf_size - 1);
 284         buf->offset = length;
 285 }
 286
 287 /*
 288  * exported relay file operations, kernel/relay.c
 289  */
 290 extern const struct file_operations relay_file_operations;
 291
 292 #ifdef CONFIG_RELAY
 293 int relay_prepare_cpu(unsigned int cpu);
 294 #else
 295 #define relay_prepare_cpu     NULL
 296 #endif
 297
 298 #endif /* _LINUX_RELAY_H */
 299