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         const 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          * This callback is optional.
  93          *
  94          * NOTE: subbuf_start will also be invoked when the buffer is
  95          *       created, so that the first sub-buffer can be initialized
  96          *       if necessary.  In this case, prev_subbuf will be NULL.
  97          *
  98          * NOTE: the client can reserve bytes at the beginning of the new
  99          *       sub-buffer by calling subbuf_start_reserve() in this callback.
 100          */
 101         int (*subbuf_start) (struct rchan_buf *buf,
 102                              void *subbuf,
 103                              void *prev_subbuf,
 104                              size_t prev_padding);
 105
 106         /*
 107          * create_buf_file - create file to represent a relay channel buffer
 108          * @filename: the name of the file to create
 109          * @parent: the parent of the file to create
 110          * @mode: the mode of the file to create
 111          * @buf: the channel buffer
 112          * @is_global: outparam - set non-zero if the buffer should be global
 113          *
 114          * Called during relay_open(), once for each per-cpu buffer,
 115          * to allow the client to create a file to be used to
 116          * represent the corresponding channel buffer.  If the file is
 117          * created outside of relay, the parent must also exist in
 118          * that filesystem.
 119          *
 120          * The callback should return the dentry of the file created
 121          * to represent the relay buffer.
 122          *
 123          * Setting the is_global outparam to a non-zero value will
 124          * cause relay_open() to create a single global buffer rather
 125          * than the default set of per-cpu buffers.
 126          *
 127          * This callback is mandatory.
 128          *
 129          * See Documentation/filesystems/relay.rst for more info.
 130          */
 131         struct dentry *(*create_buf_file)(const char *filename,
 132                                           struct dentry *parent,
 133                                           umode_t mode,
 134                                           struct rchan_buf *buf,
 135                                           int *is_global);
 136
 137         /*
 138          * remove_buf_file - remove file representing a relay channel buffer
 139          * @dentry: the dentry of the file to remove
 140          *
 141          * Called during relay_close(), once for each per-cpu buffer,
 142          * to allow the client to remove a file used to represent a
 143          * channel buffer.
 144          *
 145          * The callback should return 0 if successful, negative if not.
 146          *
 147          * This callback is mandatory.
 148          */
 149         int (*remove_buf_file)(struct dentry *dentry);
 150 };
 151
 152 /*
 153  * CONFIG_RELAY kernel API, kernel/relay.c
 154  */
 155
 156 struct rchan *relay_open(const char *base_filename,
 157                          struct dentry *parent,
 158                          size_t subbuf_size,
 159                          size_t n_subbufs,
 160                          const struct rchan_callbacks *cb,
 161                          void *private_data);
 162 extern int relay_late_setup_files(struct rchan *chan,
 163                                   const char *base_filename,
 164                                   struct dentry *parent);
 165 extern void relay_close(struct rchan *chan);
 166 extern void relay_flush(struct rchan *chan);
 167 extern void relay_subbufs_consumed(struct rchan *chan,
 168                                    unsigned int cpu,
 169                                    size_t consumed);
 170 extern void relay_reset(struct rchan *chan);
 171 extern int relay_buf_full(struct rchan_buf *buf);
 172
 173 extern size_t relay_switch_subbuf(struct rchan_buf *buf,
 174                                   size_t length);
 175
 176 /**
 177  *      relay_write - write data into the channel
 178  *      @chan: relay channel
 179  *      @data: data to be written
 180  *      @length: number of bytes to write
 181  *
 182  *      Writes data into the current cpu's channel buffer.
 183  *
 184  *      Protects the buffer by disabling interrupts.  Use this
 185  *      if you might be logging from interrupt context.  Try
 186  *      __relay_write() if you know you won't be logging from
 187  *      interrupt context.
 188  */
 189 static inline void relay_write(struct rchan *chan,
 190                                const void *data,
 191                                size_t length)
 192 {
 193         unsigned long flags;
 194         struct rchan_buf *buf;
 195
 196         local_irq_save(flags);
 197         buf = *this_cpu_ptr(chan->buf);
 198         if (unlikely(buf->offset + length > chan->subbuf_size))
 199                 length = relay_switch_subbuf(buf, length);
 200         memcpy(buf->data + buf->offset, data, length);
 201         buf->offset += length;
 202         local_irq_restore(flags);
 203 }
 204
 205 /**
 206  *      __relay_write - write data into the channel
 207  *      @chan: relay channel
 208  *      @data: data to be written
 209  *      @length: number of bytes to write
 210  *
 211  *      Writes data into the current cpu's channel buffer.
 212  *
 213  *      Protects the buffer by disabling preemption.  Use
 214  *      relay_write() if you might be logging from interrupt
 215  *      context.
 216  */
 217 static inline void __relay_write(struct rchan *chan,
 218                                  const void *data,
 219                                  size_t length)
 220 {
 221         struct rchan_buf *buf;
 222
 223         buf = *get_cpu_ptr(chan->buf);
 224         if (unlikely(buf->offset + length > buf->chan->subbuf_size))
 225                 length = relay_switch_subbuf(buf, length);
 226         memcpy(buf->data + buf->offset, data, length);
 227         buf->offset += length;
 228         put_cpu_ptr(chan->buf);
 229 }
 230
 231 /**
 232  *      relay_reserve - reserve slot in channel buffer
 233  *      @chan: relay channel
 234  *      @length: number of bytes to reserve
 235  *
 236  *      Returns pointer to reserved slot, NULL if full.
 237  *
 238  *      Reserves a slot in the current cpu's channel buffer.
 239  *      Does not protect the buffer at all - caller must provide
 240  *      appropriate synchronization.
 241  */
 242 static inline void *relay_reserve(struct rchan *chan, size_t length)
 243 {
 244         void *reserved = NULL;
 245         struct rchan_buf *buf = *get_cpu_ptr(chan->buf);
 246
 247         if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
 248                 length = relay_switch_subbuf(buf, length);
 249                 if (!length)
 250                         goto end;
 251         }
 252         reserved = buf->data + buf->offset;
 253         buf->offset += length;
 254
 255 end:
 256         put_cpu_ptr(chan->buf);
 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 const struct file_operations relay_file_operations;
 279
 280 #ifdef CONFIG_RELAY
 281 int relay_prepare_cpu(unsigned int cpu);
 282 #else
 283 #define relay_prepare_cpu     NULL
 284 #endif
 285
 286 #endif /* _LINUX_RELAY_H */
 287