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         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
  87         void *p;
  88
  89         if (caa_unlikely(!len))
  90                 return;
  91         offset &= chanb->buf_size - 1;
  92         sbidx = offset >> chanb->subbuf_size_order;
  93         id = shmp_index(handle, bufb->buf_wsb, sbidx)->id;
  94         sb_bindex = subbuffer_id_get_index(config, id);
  95         rpages = shmp_index(handle, bufb->array, sb_bindex);
  96         if (caa_unlikely(!rpages))
  97                 return;
  98         CHAN_WARN_ON(ctx->chan,
  99                      config->mode == RING_BUFFER_OVERWRITE
 100                      && subbuffer_id_is_noref(config, id));
 101         /*
 102          * Underlying layer should never ask for writes across
 103          * subbuffers.
 104          */
 105         CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
 106         backend_pages = shmp(handle, rpages->shmp);
 107         if (caa_unlikely(!backend_pages))
 108                 return;
 109         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 110         if (caa_unlikely(!p))
 111                 return;
 112         lib_ring_buffer_do_copy(config, p, src, len);
 113         ctx->buf_offset += len;
 114 }
 115
 116 /*
 117  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 118  * terminating character is found in @src. Returns the number of bytes
 119  * copied. Does *not* terminate @dest with NULL terminating character.
 120  */
 121 static inline
 122 size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 123                 char *dest, const char *src, size_t len)
 124 {
 125         size_t count;
 126
 127         for (count = 0; count < len; count++) {
 128                 char c;
 129
 130                 /*
 131                  * Only read source character once, in case it is
 132                  * modified concurrently.
 133                  */
 134                 c = CMM_LOAD_SHARED(src[count]);
 135                 if (!c)
 136                         break;
 137                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 138         }
 139         return count;
 140 }
 141
 142 /**
 143  * lib_ring_buffer_strcpy - write string data to a buffer backend
 144  * @config : ring buffer instance configuration
 145  * @ctx: ring buffer context. (input arguments only)
 146  * @src : source pointer to copy from
 147  * @len : length of data to copy
 148  * @pad : character to use for padding
 149  *
 150  * This function copies @len - 1 bytes of string data from a source
 151  * pointer to a buffer backend, followed by a terminating '\0'
 152  * character, at the current context offset. This is more or less a
 153  * buffer backend-specific strncpy() operation. If a terminating '\0'
 154  * character is found in @src before @len - 1 characters are copied, pad
 155  * the buffer with @pad characters (e.g. '#').
 156  */
 157 static inline
 158 void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 159                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 160                            const char *src, size_t len, int pad)
 161 {
 162         struct lttng_ust_lib_ring_buffer_backend *bufb = &ctx->buf->backend;
 163         struct channel_backend *chanb = &ctx->chan->backend;
 164         struct lttng_ust_shm_handle *handle = ctx->handle;
 165         size_t sbidx, count;
 166         size_t offset = ctx->buf_offset;
 167         struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 168         unsigned long sb_bindex, id;
 169
 170         if (caa_unlikely(!len))
 171                 return;
 172         offset &= chanb->buf_size - 1;
 173         sbidx = offset >> chanb->subbuf_size_order;
 174         id = shmp_index(handle, bufb->buf_wsb, sbidx)->id;
 175         sb_bindex = subbuffer_id_get_index(config, id);
 176         rpages = shmp_index(handle, bufb->array, sb_bindex);
 177         CHAN_WARN_ON(ctx->chan,
 178                      config->mode == RING_BUFFER_OVERWRITE
 179                      && subbuffer_id_is_noref(config, id));
 180         /*
 181          * Underlying layer should never ask for writes across
 182          * subbuffers.
 183          */
 184         CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
 185         count = lib_ring_buffer_do_strcpy(config,
 186                         shmp_index(handle, shmp(handle, rpages->shmp)->p,
 187                                 offset & (chanb->subbuf_size - 1)),
 188                         src, len - 1);
 189         offset += count;
 190         /* Padding */
 191         if (caa_unlikely(count < len - 1)) {
 192                 size_t pad_len = len - 1 - count;
 193
 194                 lib_ring_buffer_do_memset(shmp_index(handle, shmp(handle, rpages->shmp)->p,
 195                                 offset & (chanb->subbuf_size - 1)),
 196                         pad, pad_len);
 197                 offset += pad_len;
 198         }
 199         /* Final '\0' */
 200         lib_ring_buffer_do_memset(shmp_index(handle, shmp(handle, rpages->shmp)->p,
 201                                 offset & (chanb->subbuf_size - 1)),
 202                         '\0', 1);
 203         ctx->buf_offset += len;
 204 }
 205
 206 /*
 207  * This accessor counts the number of unread records in a buffer.
 208  * It only provides a consistent value if no reads not writes are performed
 209  * concurrently.
 210  */
 211 static inline
 212 unsigned long lib_ring_buffer_get_records_unread(
 213                                 const struct lttng_ust_lib_ring_buffer_config *config,
 214                                 struct lttng_ust_lib_ring_buffer *buf,
 215                                 struct lttng_ust_shm_handle *handle)
 216 {
 217         struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
 218         unsigned long records_unread = 0, sb_bindex;
 219         unsigned int i;
 220         struct channel *chan;
 221
 222         chan = shmp(handle, bufb->chan);
 223         if (!chan)
 224                 return 0;
 225         for (i = 0; i < chan->backend.num_subbuf; i++) {
 226                 struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 227                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 228                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 229
 230                 wsb = shmp_index(handle, bufb->buf_wsb, i);
 231                 if (!wsb)
 232                         return 0;
 233                 sb_bindex = subbuffer_id_get_index(config, wsb->id);
 234                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 235                 if (!rpages)
 236                         return 0;
 237                 backend_pages = shmp(handle, rpages->shmp);
 238                 if (!backend_pages)
 239                         return 0;
 240                 records_unread += v_read(config, &backend_pages->records_unread);
 241         }
 242         if (config->mode == RING_BUFFER_OVERWRITE) {
 243                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 244                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 245
 246                 sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 247                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 248                 if (!rpages)
 249                         return 0;
 250                 backend_pages = shmp(handle, rpages->shmp);
 251                 if (!backend_pages)
 252                         return 0;
 253                 records_unread += v_read(config, &backend_pages->records_unread);
 254         }
 255         return records_unread;
 256 }
 257
 258 #endif /* _LTTNG_RING_BUFFER_BACKEND_H */