include/linux/relay.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * linux/include/linux/relay.h
   4  *
   5  * Copyright (C) 2002, 2003 - Tom Zanussi (zanussi@us.ibm.com), IBM Corp
   6  * Copyright (C) 1999, 2000, 2001, 2002 - Karim Yaghmour (karim@opersys.com)
   7  *
   8  * CONFIG_RELAY definitions and declarations
   9  */
  10
  11 #ifndef _LINUX_RELAY_H
  12 #define _LINUX_RELAY_H
  13
  14 #include <linux/types.h>
  15 #include <linux/sched.h>
  16 #include <linux/timer.h>
  17 #include <linux/wait.h>
  18 #include <linux/list.h>
  19 #include <linux/irq_work.h>
  20 #include <linux/bug.h>
  21 #include <linux/fs.h>
  22 #include <linux/poll.h>
  23 #include <linux/kref.h>
  24 #include <linux/percpu.h>
  25
  26 /*
  27  * Tracks changes to rchan/rchan_buf structs
  28  */
  29 #define RELAYFS_CHANNEL_VERSION         7
  30
  31 /*
  32  * Per-cpu relay channel buffer
  33  */
  34 struct rchan_buf
  35 {
  36         void *start;                    /* start of channel buffer */
  37         void *data;                     /* start of current sub-buffer */
  38         size_t offset;                  /* current offset into sub-buffer */
  39         size_t subbufs_produced;        /* count of sub-buffers produced */
  40         size_t subbufs_consumed;        /* count of sub-buffers consumed */
  41         struct rchan *chan;             /* associated channel */
  42         wait_queue_head_t read_wait;    /* reader wait queue */
  43         struct irq_work wakeup_work;    /* reader wakeup */
  44         struct dentry *dentry;          /* channel file dentry */
  45         struct kref kref;               /* channel buffer refcount */
  46         struct page **page_array;       /* array of current buffer pages */
  47         unsigned int page_count;        /* number of current buffer pages */
  48         unsigned int finalized;         /* buffer has been finalized */
  49         size_t *padding;                /* padding counts per sub-buffer */
  50         size_t prev_padding;            /* temporary variable */
  51         size_t bytes_consumed;          /* bytes consumed in cur read subbuf */
  52         size_t early_bytes;             /* bytes consumed before VFS inited */
  53         unsigned int cpu;               /* this buf's cpu */
  54 } ____cacheline_aligned;
  55
  56 /*
  57  * Relay channel data structure
  58  */
  59 struct rchan
  60 {
  61         u32 version;                    /* the version of this struct */
  62         size_t subbuf_size;             /* sub-buffer size */
  63         size_t n_subbufs;               /* number of sub-buffers per buffer */
  64         size_t alloc_size;              /* total buffer size allocated */
  65         struct rchan_callbacks *cb;     /* client callbacks */
  66         struct kref kref;               /* channel refcount */
  67         void *private_data;             /* for user-defined data */
  68         size_t last_toobig;             /* tried to log event > subbuf size */
  69         struct rchan_buf ** __percpu buf; /* per-cpu channel buffers */
  70         int is_global;                  /* One global buffer ? */
  71         struct list_head list;          /* for channel list */
  72         struct dentry *parent;          /* parent dentry passed to open */
  73         int has_base_filename;          /* has a filename associated? */
  74         char base_filename[NAME_MAX];   /* saved base filename */
  75 };
  76
  77 /*
  78  * Relay channel client callbacks
  79  */
  80 struct rchan_callbacks
  81 {
  82         /*
  83          * subbuf_start - called on buffer-switch to a new sub-buffer
  84          * @buf: the channel buffer containing the new sub-buffer
  85          * @subbuf: the start of the new sub-buffer
  86          * @prev_subbuf: the start of the previous sub-buffer
  87          * @prev_padding: unused space at the end of previous sub-buffer
  88          *
  89          * The client should return 1 to continue logging, 0 to stop
  90          * logging.
  91          *
  92          * NOTE: subbuf_start will also be invoked when the buffer is
  93          *       created, so that the first sub-buffer can be initialized
  94          *       if necessary.  In this case, prev_subbuf will be NULL.
  95          *
  96          * NOTE: the client can reserve bytes at the beginning of the new
  97          *       sub-buffer by calling subbuf_start_reserve() in this callback.
  98          */
  99         int (*subbuf_start) (struct rchan_buf *buf,
 100                              void *subbuf,
 101                              void *prev_subbuf,
 102                              size_t prev_padding);
 103
 104         /*
 105          * buf_mapped - relay buffer mmap notification
 106          * @buf: the channel buffer
 107          * @filp: relay file pointer
 108          *
 109          * Called when a relay file is successfully mmapped
 110          */
 111         void (*buf_mapped)(struct rchan_buf *buf,
 112                            struct file *filp);
 113
 114         /*
 115          * buf_unmapped - relay buffer unmap notification
 116          * @buf: the channel buffer
 117          * @filp: relay file pointer
 118          *
 119          * Called when a relay file is successfully unmapped
 120          */
 121         void (*buf_unmapped)(struct rchan_buf *buf,
 122                              struct file *filp);
 123         /*
 124          * create_buf_file - create file to represent a relay channel buffer
 125          * @filename: the name of the file to create
 126          * @parent: the parent of the file to create
 127          * @mode: the mode of the file to create
 128          * @buf: the channel buffer
 129          * @is_global: outparam - set non-zero if the buffer should be global
 130          *
 131          * Called during relay_open(), once for each per-cpu buffer,
 132          * to allow the client to create a file to be used to
 133          * represent the corresponding channel buffer.  If the file is
 134          * created outside of relay, the parent must also exist in
 135          * that filesystem.
 136          *
 137          * The callback should return the dentry of the file created
 138          * to represent the relay buffer.
 139          *
 140          * Setting the is_global outparam to a non-zero value will
 141          * cause relay_open() to create a single global buffer rather
 142          * than the default set of per-cpu buffers.
 143          *
 144          * See Documentation/filesystems/relay.txt for more info.
 145          */
 146         struct dentry *(*create_buf_file)(const char *filename,
 147                                           struct dentry *parent,
 148                                           umode_t mode,
 149                                           struct rchan_buf *buf,
 150                                           int *is_global);
 151
 152         /*
 153          * remove_buf_file - remove file representing a relay channel buffer
 154          * @dentry: the dentry of the file to remove
 155          *
 156          * Called during relay_close(), once for each per-cpu buffer,
 157          * to allow the client to remove a file used to represent a
 158          * channel buffer.
 159          *
 160          * The callback should return 0 if successful, negative if not.
 161          */
 162         int (*remove_buf_file)(struct dentry *dentry);
 163 };
 164
 165 /*
 166  * CONFIG_RELAY kernel API, kernel/relay.c
 167  */
 168
 169 struct rchan *relay_open(const char *base_filename,
 170                          struct dentry *parent,
 171                          size_t subbuf_size,
 172                          size_t n_subbufs,
 173                          struct rchan_callbacks *cb,
 174                          void *private_data);
 175 extern int relay_late_setup_files(struct rchan *chan,
 176                                   const char *base_filename,
 177                                   struct dentry *parent);
 178 extern void relay_close(struct rchan *chan);
 179 extern void relay_flush(struct rchan *chan);
 180 extern void relay_subbufs_consumed(struct rchan *chan,
 181                                    unsigned int cpu,
 182                                    size_t consumed);
 183 extern void relay_reset(struct rchan *chan);
 184 extern int relay_buf_full(struct rchan_buf *buf);
 185
 186 extern size_t relay_switch_subbuf(struct rchan_buf *buf,
 187                                   size_t length);
 188
 189 /**
 190  *      relay_write - write data into the channel
 191  *      @chan: relay channel
 192  *      @data: data to be written
 193  *      @length: number of bytes to write
 194  *
 195  *      Writes data into the current cpu's channel buffer.
 196  *
 197  *      Protects the buffer by disabling interrupts.  Use this
 198  *      if you might be logging from interrupt context.  Try
 199  *      __relay_write() if you know you won't be logging from
 200  *      interrupt context.
 201  */
 202 static inline void relay_write(struct rchan *chan,
 203                                const void *data,
 204                                size_t length)
 205 {
 206         unsigned long flags;
 207         struct rchan_buf *buf;
 208
 209         local_irq_save(flags);
 210         buf = *this_cpu_ptr(chan->buf);
 211         if (unlikely(buf->offset + length > chan->subbuf_size))
 212                 length = relay_switch_subbuf(buf, length);
 213         memcpy(buf->data + buf->offset, data, length);
 214         buf->offset += length;
 215         local_irq_restore(flags);
 216 }
 217
 218 /**
 219  *      __relay_write - write data into the channel
 220  *      @chan: relay channel
 221  *      @data: data to be written
 222  *      @length: number of bytes to write
 223  *
 224  *      Writes data into the current cpu's channel buffer.
 225  *
 226  *      Protects the buffer by disabling preemption.  Use
 227  *      relay_write() if you might be logging from interrupt
 228  *      context.
 229  */
 230 static inline void __relay_write(struct rchan *chan,
 231                                  const void *data,
 232                                  size_t length)
 233 {
 234         struct rchan_buf *buf;
 235
 236         buf = *get_cpu_ptr(chan->buf);
 237         if (unlikely(buf->offset + length > buf->chan->subbuf_size))
 238                 length = relay_switch_subbuf(buf, length);
 239         memcpy(buf->data + buf->offset, data, length);
 240         buf->offset += length;
 241         put_cpu_ptr(chan->buf);
 242 }
 243
 244 /**
 245  *      relay_reserve - reserve slot in channel buffer
 246  *      @chan: relay channel
 247  *      @length: number of bytes to reserve
 248  *
 249  *      Returns pointer to reserved slot, NULL if full.
 250  *
 251  *      Reserves a slot in the current cpu's channel buffer.
 252  *      Does not protect the buffer at all - caller must provide
 253  *      appropriate synchronization.
 254  */
 255 static inline void *relay_reserve(struct rchan *chan, size_t length)
 256 {
 257         void *reserved = NULL;
 258         struct rchan_buf *buf = *get_cpu_ptr(chan->buf);
 259
 260         if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
 261                 length = relay_switch_subbuf(buf, length);
 262                 if (!length)
 263                         goto end;
 264         }
 265         reserved = buf->data + buf->offset;
 266         buf->offset += length;
 267
 268 end:
 269         put_cpu_ptr(chan->buf);
 270         return reserved;
 271 }
 272
 273 /**
 274  *      subbuf_start_reserve - reserve bytes at the start of a sub-buffer
 275  *      @buf: relay channel buffer
 276  *      @length: number of bytes to reserve
 277  *
 278  *      Helper function used to reserve bytes at the beginning of
 279  *      a sub-buffer in the subbuf_start() callback.
 280  */
 281 static inline void subbuf_start_reserve(struct rchan_buf *buf,
 282                                         size_t length)
 283 {
 284         BUG_ON(length >= buf->chan->subbuf_size - 1);
 285         buf->offset = length;
 286 }
 287
 288 /*
 289  * exported relay file operations, kernel/relay.c
 290  */
 291 extern const struct file_operations relay_file_operations;
 292
 293 #ifdef CONFIG_RELAY
 294 int relay_prepare_cpu(unsigned int cpu);
 295 #else
 296 #define relay_prepare_cpu     NULL
 297 #endif
 298
 299 #endif /* _LINUX_RELAY_H */
 300