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 __attribute__((always_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 channel_backend *chanb = &ctx->chan->backend;
  80         struct lttng_ust_shm_handle *handle = ctx->handle;
  81         size_t offset = ctx->buf_offset;
  82         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
  83         void *p;
  84
  85         if (caa_unlikely(!len))
  86                 return;
  87         /*
  88          * Underlying layer should never ask for writes across
  89          * subbuffers.
  90          */
  91         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
  92         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
  93         if (caa_unlikely(!backend_pages)) {
  94                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
  95                         return;
  96         }
  97         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
  98         if (caa_unlikely(!p))
  99                 return;
 100         lib_ring_buffer_do_copy(config, p, src, len);
 101         ctx->buf_offset += len;
 102 }
 103
 104 /*
 105  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 106  * terminating character is found in @src. Returns the number of bytes
 107  * copied. Does *not* terminate @dest with NULL terminating character.
 108  */
 109 static inline __attribute__((always_inline))
 110 size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 111                 char *dest, const char *src, size_t len)
 112 {
 113         size_t count;
 114
 115         for (count = 0; count < len; count++) {
 116                 char c;
 117
 118                 /*
 119                  * Only read source character once, in case it is
 120                  * modified concurrently.
 121                  */
 122                 c = CMM_LOAD_SHARED(src[count]);
 123                 if (!c)
 124                         break;
 125                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 126         }
 127         return count;
 128 }
 129
 130 /**
 131  * lib_ring_buffer_strcpy - write string data to a buffer backend
 132  * @config : ring buffer instance configuration
 133  * @ctx: ring buffer context. (input arguments only)
 134  * @src : source pointer to copy from
 135  * @len : length of data to copy
 136  * @pad : character to use for padding
 137  *
 138  * This function copies @len - 1 bytes of string data from a source
 139  * pointer to a buffer backend, followed by a terminating '\0'
 140  * character, at the current context offset. This is more or less a
 141  * buffer backend-specific strncpy() operation. If a terminating '\0'
 142  * character is found in @src before @len - 1 characters are copied, pad
 143  * the buffer with @pad characters (e.g. '#').
 144  */
 145 static inline __attribute__((always_inline))
 146 void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 147                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 148                            const char *src, size_t len, int pad)
 149 {
 150         struct channel_backend *chanb = &ctx->chan->backend;
 151         struct lttng_ust_shm_handle *handle = ctx->handle;
 152         size_t count;
 153         size_t offset = ctx->buf_offset;
 154         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 155         void *p;
 156
 157         if (caa_unlikely(!len))
 158                 return;
 159         /*
 160          * Underlying layer should never ask for writes across
 161          * subbuffers.
 162          */
 163         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
 164         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 165         if (caa_unlikely(!backend_pages)) {
 166                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
 167                         return;
 168         }
 169         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 170         if (caa_unlikely(!p))
 171                 return;
 172
 173         count = lib_ring_buffer_do_strcpy(config, p, src, len - 1);
 174         offset += count;
 175         /* Padding */
 176         if (caa_unlikely(count < len - 1)) {
 177                 size_t pad_len = len - 1 - count;
 178
 179                 p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 180                 if (caa_unlikely(!p))
 181                         return;
 182                 lib_ring_buffer_do_memset(p, pad, pad_len);
 183                 offset += pad_len;
 184         }
 185         /* Final '\0' */
 186         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 187         if (caa_unlikely(!p))
 188                 return;
 189         lib_ring_buffer_do_memset(p, '\0', 1);
 190         ctx->buf_offset += len;
 191 }
 192
 193 /*
 194  * This accessor counts the number of unread records in a buffer.
 195  * It only provides a consistent value if no reads not writes are performed
 196  * concurrently.
 197  */
 198 static inline
 199 unsigned long lib_ring_buffer_get_records_unread(
 200                                 const struct lttng_ust_lib_ring_buffer_config *config,
 201                                 struct lttng_ust_lib_ring_buffer *buf,
 202                                 struct lttng_ust_shm_handle *handle)
 203 {
 204         struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
 205         unsigned long records_unread = 0, sb_bindex;
 206         unsigned int i;
 207         struct channel *chan;
 208
 209         chan = shmp(handle, bufb->chan);
 210         if (!chan)
 211                 return 0;
 212         for (i = 0; i < chan->backend.num_subbuf; i++) {
 213                 struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 214                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 215                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 216
 217                 wsb = shmp_index(handle, bufb->buf_wsb, i);
 218                 if (!wsb)
 219                         return 0;
 220                 sb_bindex = subbuffer_id_get_index(config, wsb->id);
 221                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 222                 if (!rpages)
 223                         return 0;
 224                 backend_pages = shmp(handle, rpages->shmp);
 225                 if (!backend_pages)
 226                         return 0;
 227                 records_unread += v_read(config, &backend_pages->records_unread);
 228         }
 229         if (config->mode == RING_BUFFER_OVERWRITE) {
 230                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 231                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 232
 233                 sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.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         return records_unread;
 243 }
 244
 245 #endif /* _LTTNG_RING_BUFFER_BACKEND_H */