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 <stddef.h>
  30 #include <unistd.h>
  31
  32 /* Internal helpers */
  33 #include "backend_internal.h"
  34 #include "frontend_internal.h"
  35
  36 /* Ring buffer backend API */
  37
  38 /* Ring buffer backend access (read/write) */
  39
  40 extern size_t lib_ring_buffer_read(struct lttng_ust_lib_ring_buffer_backend *bufb,
  41                                    size_t offset, void *dest, size_t len,
  42                                    struct lttng_ust_shm_handle *handle);
  43
  44 extern int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb,
  45                                      size_t offset, void *dest, size_t len,
  46                                      struct lttng_ust_shm_handle *handle);
  47
  48 /*
  49  * Return the address where a given offset is located.
  50  * Should be used to get the current subbuffer header pointer. Given we know
  51  * it's never on a page boundary, it's safe to write directly to this address,
  52  * as long as the write is never bigger than a page size.
  53  */
  54 extern void *
  55 lib_ring_buffer_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
  56                                size_t offset,
  57                                struct lttng_ust_shm_handle *handle);
  58 extern void *
  59 lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
  60                                     size_t offset,
  61                                     struct lttng_ust_shm_handle *handle);
  62
  63 /**
  64  * lib_ring_buffer_write - write data to a buffer backend
  65  * @config : ring buffer instance configuration
  66  * @ctx: ring buffer context. (input arguments only)
  67  * @src : source pointer to copy from
  68  * @len : length of data to copy
  69  *
  70  * This function copies "len" bytes of data from a source pointer to a buffer
  71  * backend, at the current context offset. This is more or less a buffer
  72  * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
  73  * if copy is crossing a page boundary.
  74  */
  75 static inline __attribute__((always_inline))
  76 void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config,
  77                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
  78                            const void *src, size_t len)
  79 {
  80         struct channel_backend *chanb = &ctx->chan->backend;
  81         struct lttng_ust_shm_handle *handle = ctx->handle;
  82         size_t offset = ctx->buf_offset;
  83         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
  84         void *p;
  85
  86         if (caa_unlikely(!len))
  87                 return;
  88         /*
  89          * Underlying layer should never ask for writes across
  90          * subbuffers.
  91          */
  92         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
  93         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
  94         if (caa_unlikely(!backend_pages)) {
  95                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
  96                         return;
  97         }
  98         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
  99         if (caa_unlikely(!p))
 100                 return;
 101         lib_ring_buffer_do_copy(config, p, src, len);
 102         ctx->buf_offset += len;
 103 }
 104
 105 /*
 106  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 107  * terminating character is found in @src. Returns the number of bytes
 108  * copied. Does *not* terminate @dest with NULL terminating character.
 109  */
 110 static inline __attribute__((always_inline))
 111 size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 112                 char *dest, const char *src, size_t len)
 113 {
 114         size_t count;
 115
 116         for (count = 0; count < len; count++) {
 117                 char c;
 118
 119                 /*
 120                  * Only read source character once, in case it is
 121                  * modified concurrently.
 122                  */
 123                 c = CMM_LOAD_SHARED(src[count]);
 124                 if (!c)
 125                         break;
 126                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 127         }
 128         return count;
 129 }
 130
 131 /**
 132  * lib_ring_buffer_strcpy - write string data to a buffer backend
 133  * @config : ring buffer instance configuration
 134  * @ctx: ring buffer context. (input arguments only)
 135  * @src : source pointer to copy from
 136  * @len : length of data to copy
 137  * @pad : character to use for padding
 138  *
 139  * This function copies @len - 1 bytes of string data from a source
 140  * pointer to a buffer backend, followed by a terminating '\0'
 141  * character, at the current context offset. This is more or less a
 142  * buffer backend-specific strncpy() operation. If a terminating '\0'
 143  * character is found in @src before @len - 1 characters are copied, pad
 144  * the buffer with @pad characters (e.g. '#').
 145  */
 146 static inline __attribute__((always_inline))
 147 void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 148                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 149                            const char *src, size_t len, int pad)
 150 {
 151         struct channel_backend *chanb = &ctx->chan->backend;
 152         struct lttng_ust_shm_handle *handle = ctx->handle;
 153         size_t count;
 154         size_t offset = ctx->buf_offset;
 155         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 156         void *p;
 157
 158         if (caa_unlikely(!len))
 159                 return;
 160         /*
 161          * Underlying layer should never ask for writes across
 162          * subbuffers.
 163          */
 164         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
 165         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 166         if (caa_unlikely(!backend_pages)) {
 167                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
 168                         return;
 169         }
 170         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 171         if (caa_unlikely(!p))
 172                 return;
 173
 174         count = lib_ring_buffer_do_strcpy(config, p, src, len - 1);
 175         offset += count;
 176         /* Padding */
 177         if (caa_unlikely(count < len - 1)) {
 178                 size_t pad_len = len - 1 - count;
 179
 180                 p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 181                 if (caa_unlikely(!p))
 182                         return;
 183                 lib_ring_buffer_do_memset(p, pad, pad_len);
 184                 offset += pad_len;
 185         }
 186         /* Final '\0' */
 187         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 188         if (caa_unlikely(!p))
 189                 return;
 190         lib_ring_buffer_do_memset(p, '\0', 1);
 191         ctx->buf_offset += len;
 192 }
 193
 194 /*
 195  * This accessor counts the number of unread records in a buffer.
 196  * It only provides a consistent value if no reads not writes are performed
 197  * concurrently.
 198  */
 199 static inline
 200 unsigned long lib_ring_buffer_get_records_unread(
 201                                 const struct lttng_ust_lib_ring_buffer_config *config,
 202                                 struct lttng_ust_lib_ring_buffer *buf,
 203                                 struct lttng_ust_shm_handle *handle)
 204 {
 205         struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
 206         unsigned long records_unread = 0, sb_bindex;
 207         unsigned int i;
 208         struct channel *chan;
 209
 210         chan = shmp(handle, bufb->chan);
 211         if (!chan)
 212                 return 0;
 213         for (i = 0; i < chan->backend.num_subbuf; i++) {
 214                 struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 215                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 216                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 217
 218                 wsb = shmp_index(handle, bufb->buf_wsb, i);
 219                 if (!wsb)
 220                         return 0;
 221                 sb_bindex = subbuffer_id_get_index(config, wsb->id);
 222                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 223                 if (!rpages)
 224                         return 0;
 225                 backend_pages = shmp(handle, rpages->shmp);
 226                 if (!backend_pages)
 227                         return 0;
 228                 records_unread += v_read(config, &backend_pages->records_unread);
 229         }
 230         if (config->mode == RING_BUFFER_OVERWRITE) {
 231                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 232                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 233
 234                 sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 235                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 236                 if (!rpages)
 237                         return 0;
 238                 backend_pages = shmp(handle, rpages->shmp);
 239                 if (!backend_pages)
 240                         return 0;
 241                 records_unread += v_read(config, &backend_pages->records_unread);
 242         }
 243         return records_unread;
 244 }
 245
 246 #endif /* _LTTNG_RING_BUFFER_BACKEND_H */