libringbuffer/backend.h

   1 #ifndef _LINUX_RING_BUFFER_BACKEND_H
   2 #define _LINUX_RING_BUFFER_BACKEND_H
   3
   4 /*
   5  * linux/ringbuffer/backend.h
   6  *
   7  * Copyright (C) 2008-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * Ring buffer backend (API).
  10  *
  11  * Dual LGPL v2.1/GPL v2 license.
  12  *
  13  * Credits to Steven Rostedt for proposing to use an extra-subbuffer owned by
  14  * the reader in flight recorder mode.
  15  */
  16
  17 #include <unistd.h>
  18
  19 #include "ust/core.h"
  20
  21 /* Internal helpers */
  22 #include "backend_internal.h"
  23 #include "frontend_internal.h"
  24
  25 /* Ring buffer backend API */
  26
  27 /* Ring buffer backend access (read/write) */
  28
  29 extern size_t lib_ring_buffer_read(struct lib_ring_buffer_backend *bufb,
  30                                    size_t offset, void *dest, size_t len);
  31
  32 extern int lib_ring_buffer_read_cstr(struct lib_ring_buffer_backend *bufb,
  33                                      size_t offset, void *dest, size_t len);
  34
  35 /*
  36  * Return the address where a given offset is located.
  37  * Should be used to get the current subbuffer header pointer. Given we know
  38  * it's never on a page boundary, it's safe to write directly to this address,
  39  * as long as the write is never bigger than a page size.
  40  */
  41 extern void *
  42 lib_ring_buffer_offset_address(struct lib_ring_buffer_backend *bufb,
  43                                size_t offset);
  44 extern void *
  45 lib_ring_buffer_read_offset_address(struct lib_ring_buffer_backend *bufb,
  46                                     size_t offset);
  47
  48 /**
  49  * lib_ring_buffer_write - write data to a buffer backend
  50  * @config : ring buffer instance configuration
  51  * @ctx: ring buffer context. (input arguments only)
  52  * @src : source pointer to copy from
  53  * @len : length of data to copy
  54  *
  55  * This function copies "len" bytes of data from a source pointer to a buffer
  56  * backend, at the current context offset. This is more or less a buffer
  57  * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
  58  * if copy is crossing a page boundary.
  59  */
  60 static inline
  61 void lib_ring_buffer_write(const struct lib_ring_buffer_config *config,
  62                            struct lib_ring_buffer_ctx *ctx,
  63                            const void *src, size_t len)
  64 {
  65         struct lib_ring_buffer_backend *bufb = &ctx->buf->backend;
  66         struct channel_backend *chanb = &ctx->chan->backend;
  67         size_t sbidx;
  68         size_t offset = ctx->buf_offset;
  69         struct lib_ring_buffer_backend_pages *rpages;
  70         unsigned long sb_bindex, id;
  71
  72         offset &= chanb->buf_size - 1;
  73         sbidx = offset >> chanb->subbuf_size_order;
  74         id = shmp(bufb->buf_wsb)[sbidx].id;
  75         sb_bindex = subbuffer_id_get_index(config, id);
  76         rpages = shmp(bufb->array)[sb_bindex];
  77         CHAN_WARN_ON(ctx->chan,
  78                      config->mode == RING_BUFFER_OVERWRITE
  79                      && subbuffer_id_is_noref(config, id));
  80         /*
  81          * Underlying layer should never ask for writes across
  82          * subbuffers.
  83          */
  84         CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
  85         lib_ring_buffer_do_copy(config,
  86                                 shmp(rpages->p) + (offset & ~(chanb->subbuf_size - 1)),
  87                                 src, len);
  88         ctx->buf_offset += len;
  89 }
  90
  91 /*
  92  * This accessor counts the number of unread records in a buffer.
  93  * It only provides a consistent value if no reads not writes are performed
  94  * concurrently.
  95  */
  96 static inline
  97 unsigned long lib_ring_buffer_get_records_unread(
  98                                 const struct lib_ring_buffer_config *config,
  99                                 struct lib_ring_buffer *buf)
 100 {
 101         struct lib_ring_buffer_backend *bufb = &buf->backend;
 102         struct lib_ring_buffer_backend_pages *pages;
 103         unsigned long records_unread = 0, sb_bindex, id;
 104         unsigned int i;
 105
 106         for (i = 0; i < shmp(bufb->chan)->backend.num_subbuf; i++) {
 107                 id = shmp(bufb->buf_wsb)[i].id;
 108                 sb_bindex = subbuffer_id_get_index(config, id);
 109                 pages = shmp(bufb->array)[sb_bindex];
 110                 records_unread += v_read(config, &pages->records_unread);
 111         }
 112         if (config->mode == RING_BUFFER_OVERWRITE) {
 113                 id = bufb->buf_rsb.id;
 114                 sb_bindex = subbuffer_id_get_index(config, id);
 115                 pages = shmp(bufb->array)[sb_bindex];
 116                 records_unread += v_read(config, &pages->records_unread);
 117         }
 118         return records_unread;
 119 }
 120
 121 #endif /* _LINUX_RING_BUFFER_BACKEND_H */