libringbuffer/backend.h

   1 #ifndef _LTTNG_RING_BUFFER_BACKEND_H
   2 #define _LTTNG_RING_BUFFER_BACKEND_H
   3
   4 /*
   5  * libringbuffer/backend.h
   6  *
   7  * Ring buffer backend (API).
   8  *
   9  * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  10  *
  11  * This library is free software; you can redistribute it and/or
  12  * modify it under the terms of the GNU Lesser General Public
  13  * License as published by the Free Software Foundation; only
  14  * version 2.1 of the License.
  15  *
  16  * This library is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  19  * Lesser General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU Lesser General Public
  22  * License along with this library; if not, write to the Free Software
  23  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  24  *
  25  * Credits to Steven Rostedt for proposing to use an extra-subbuffer owned by
  26  * the reader in flight recorder mode.
  27  */
  28
  29 #include <unistd.h>
  30
  31 /* Internal helpers */
  32 #include "backend_internal.h"
  33 #include "frontend_internal.h"
  34
  35 /* Ring buffer backend API */
  36
  37 /* Ring buffer backend access (read/write) */
  38
  39 extern size_t lib_ring_buffer_read(struct lttng_ust_lib_ring_buffer_backend *bufb,
  40                                    size_t offset, void *dest, size_t len,
  41                                    struct lttng_ust_shm_handle *handle);
  42
  43 extern int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb,
  44                                      size_t offset, void *dest, size_t len,
  45                                      struct lttng_ust_shm_handle *handle);
  46
  47 /*
  48  * Return the address where a given offset is located.
  49  * Should be used to get the current subbuffer header pointer. Given we know
  50  * it's never on a page boundary, it's safe to write directly to this address,
  51  * as long as the write is never bigger than a page size.
  52  */
  53 extern void *
  54 lib_ring_buffer_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
  55                                size_t offset,
  56                                struct lttng_ust_shm_handle *handle);
  57 extern void *
  58 lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
  59                                     size_t offset,
  60                                     struct lttng_ust_shm_handle *handle);
  61
  62 /**
  63  * lib_ring_buffer_write - write data to a buffer backend
  64  * @config : ring buffer instance configuration
  65  * @ctx: ring buffer context. (input arguments only)
  66  * @src : source pointer to copy from
  67  * @len : length of data to copy
  68  *
  69  * This function copies "len" bytes of data from a source pointer to a buffer
  70  * backend, at the current context offset. This is more or less a buffer
  71  * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
  72  * if copy is crossing a page boundary.
  73  */
  74 static inline
  75 void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config,
  76                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
  77                            const void *src, size_t len)
  78 {
  79         struct lttng_ust_lib_ring_buffer_backend *bufb = &ctx->buf->backend;
  80         struct channel_backend *chanb = &ctx->chan->backend;
  81         struct lttng_ust_shm_handle *handle = ctx->handle;
  82         size_t sbidx;
  83         size_t offset = ctx->buf_offset;
  84         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
  85         unsigned long sb_bindex, id;
  86
  87         offset &= chanb->buf_size - 1;
  88         sbidx = offset >> chanb->subbuf_size_order;
  89         id = shmp_index(handle, bufb->buf_wsb, sbidx)->id;
  90         sb_bindex = subbuffer_id_get_index(config, id);
  91         rpages = shmp_index(handle, bufb->array, sb_bindex);
  92         CHAN_WARN_ON(ctx->chan,
  93                      config->mode == RING_BUFFER_OVERWRITE
  94                      && subbuffer_id_is_noref(config, id));
  95         /*
  96          * Underlying layer should never ask for writes across
  97          * subbuffers.
  98          */
  99         CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
 100         lib_ring_buffer_do_copy(config,
 101                                 shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & (chanb->subbuf_size - 1)),
 102                                 src, len);
 103         ctx->buf_offset += len;
 104 }
 105
 106 /*
 107  * This accessor counts the number of unread records in a buffer.
 108  * It only provides a consistent value if no reads not writes are performed
 109  * concurrently.
 110  */
 111 static inline
 112 unsigned long lib_ring_buffer_get_records_unread(
 113                                 const struct lttng_ust_lib_ring_buffer_config *config,
 114                                 struct lttng_ust_lib_ring_buffer *buf,
 115                                 struct lttng_ust_shm_handle *handle)
 116 {
 117         struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
 118         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
 119         unsigned long records_unread = 0, sb_bindex, id;
 120         unsigned int i;
 121
 122         for (i = 0; i < shmp(handle, bufb->chan)->backend.num_subbuf; i++) {
 123                 id = shmp_index(handle, bufb->buf_wsb, i)->id;
 124                 sb_bindex = subbuffer_id_get_index(config, id);
 125                 pages = shmp_index(handle, bufb->array, sb_bindex);
 126                 records_unread += v_read(config, &shmp(handle, pages->shmp)->records_unread);
 127         }
 128         if (config->mode == RING_BUFFER_OVERWRITE) {
 129                 id = bufb->buf_rsb.id;
 130                 sb_bindex = subbuffer_id_get_index(config, id);
 131                 pages = shmp_index(handle, bufb->array, sb_bindex);
 132                 records_unread += v_read(config, &shmp(handle, pages->shmp)->records_unread);
 133         }
 134         return records_unread;
 135 }
 136
 137 #endif /* _LTTNG_RING_BUFFER_BACKEND_H */