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         if (caa_unlikely(!len))
  88                 return;
  89         offset &= chanb->buf_size - 1;
  90         sbidx = offset >> chanb->subbuf_size_order;
  91         id = shmp_index(handle, bufb->buf_wsb, sbidx)->id;
  92         sb_bindex = subbuffer_id_get_index(config, id);
  93         rpages = shmp_index(handle, bufb->array, sb_bindex);
  94         CHAN_WARN_ON(ctx->chan,
  95                      config->mode == RING_BUFFER_OVERWRITE
  96                      && subbuffer_id_is_noref(config, id));
  97         /*
  98          * Underlying layer should never ask for writes across
  99          * subbuffers.
 100          */
 101         CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
 102         lib_ring_buffer_do_copy(config,
 103                                 shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & (chanb->subbuf_size - 1)),
 104                                 src, len);
 105         ctx->buf_offset += len;
 106 }
 107
 108 /*
 109  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 110  * terminating character is found in @src. Returns the number of bytes
 111  * copied. Does *not* terminate @dest with NULL terminating character.
 112  */
 113 static inline
 114 size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 115                 char *dest, const char *src, size_t len)
 116 {
 117         size_t count;
 118
 119         for (count = 0; count < len; count++) {
 120                 char c;
 121
 122                 /*
 123                  * Only read source character once, in case it is
 124                  * modified concurrently.
 125                  */
 126                 c = CMM_LOAD_SHARED(src[count]);
 127                 if (!c)
 128                         break;
 129                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 130         }
 131         return count;
 132 }
 133
 134 /**
 135  * lib_ring_buffer_strcpy - write string data to a buffer backend
 136  * @config : ring buffer instance configuration
 137  * @ctx: ring buffer context. (input arguments only)
 138  * @src : source pointer to copy from
 139  * @len : length of data to copy
 140  * @pad : character to use for padding
 141  *
 142  * This function copies @len - 1 bytes of string data from a source
 143  * pointer to a buffer backend, followed by a terminating '\0'
 144  * character, at the current context offset. This is more or less a
 145  * buffer backend-specific strncpy() operation. If a terminating '\0'
 146  * character is found in @src before @len - 1 characters are copied, pad
 147  * the buffer with @pad characters (e.g. '#').
 148  */
 149 static inline
 150 void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 151                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 152                            const char *src, size_t len, int pad)
 153 {
 154         struct lttng_ust_lib_ring_buffer_backend *bufb = &ctx->buf->backend;
 155         struct channel_backend *chanb = &ctx->chan->backend;
 156         struct lttng_ust_shm_handle *handle = ctx->handle;
 157         size_t sbidx, count;
 158         size_t offset = ctx->buf_offset;
 159         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 160         unsigned long sb_bindex, id;
 161
 162         if (caa_unlikely(!len))
 163                 return;
 164         offset &= chanb->buf_size - 1;
 165         sbidx = offset >> chanb->subbuf_size_order;
 166         id = shmp_index(handle, bufb->buf_wsb, sbidx)->id;
 167         sb_bindex = subbuffer_id_get_index(config, id);
 168         rpages = shmp_index(handle, bufb->array, sb_bindex);
 169         CHAN_WARN_ON(ctx->chan,
 170                      config->mode == RING_BUFFER_OVERWRITE
 171                      && subbuffer_id_is_noref(config, id));
 172         /*
 173          * Underlying layer should never ask for writes across
 174          * subbuffers.
 175          */
 176         CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
 177         count = lib_ring_buffer_do_strcpy(config,
 178                         shmp_index(handle, shmp(handle, rpages->shmp)->p,
 179                                 offset & (chanb->subbuf_size - 1)),
 180                         src, len - 1);
 181         offset += count;
 182         /* Padding */
 183         if (caa_unlikely(count < len - 1)) {
 184                 size_t pad_len = len - 1 - count;
 185
 186                 lib_ring_buffer_do_memset(shmp_index(handle, shmp(handle, rpages->shmp)->p,
 187                                 offset & (chanb->subbuf_size - 1)),
 188                         pad, pad_len);
 189                 offset += pad_len;
 190         }
 191         /* Final '\0' */
 192         lib_ring_buffer_do_memset(shmp_index(handle, shmp(handle, rpages->shmp)->p,
 193                                 offset & (chanb->subbuf_size - 1)),
 194                         '\0', 1);
 195         ctx->buf_offset += len;
 196 }
 197
 198 /*
 199  * This accessor counts the number of unread records in a buffer.
 200  * It only provides a consistent value if no reads not writes are performed
 201  * concurrently.
 202  */
 203 static inline
 204 unsigned long lib_ring_buffer_get_records_unread(
 205                                 const struct lttng_ust_lib_ring_buffer_config *config,
 206                                 struct lttng_ust_lib_ring_buffer *buf,
 207                                 struct lttng_ust_shm_handle *handle)
 208 {
 209         struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
 210         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *pages;
 211         unsigned long records_unread = 0, sb_bindex, id;
 212         unsigned int i;
 213
 214         for (i = 0; i < shmp(handle, bufb->chan)->backend.num_subbuf; i++) {
 215                 id = shmp_index(handle, bufb->buf_wsb, i)->id;
 216                 sb_bindex = subbuffer_id_get_index(config, id);
 217                 pages = shmp_index(handle, bufb->array, sb_bindex);
 218                 records_unread += v_read(config, &shmp(handle, pages->shmp)->records_unread);
 219         }
 220         if (config->mode == RING_BUFFER_OVERWRITE) {
 221                 id = bufb->buf_rsb.id;
 222                 sb_bindex = subbuffer_id_get_index(config, id);
 223                 pages = shmp_index(handle, bufb->array, sb_bindex);
 224                 records_unread += v_read(config, &shmp(handle, pages->shmp)->records_unread);
 225         }
 226         return records_unread;
 227 }
 228
 229 #endif /* _LTTNG_RING_BUFFER_BACKEND_H */