libringbuffer/backend.h

   1 /*
   2  * SPDX-License-Identifier: LGPL-2.1-only
   3  *
   4  * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   5  *
   6  * Ring buffer backend (API).
   7  *
   8  * Credits to Steven Rostedt for proposing to use an extra-subbuffer owned by
   9  * the reader in flight recorder mode.
  10  */
  11
  12 #ifndef _LTTNG_RING_BUFFER_BACKEND_H
  13 #define _LTTNG_RING_BUFFER_BACKEND_H
  14
  15 #include <stddef.h>
  16 #include <unistd.h>
  17
  18 /* Internal helpers */
  19 #include "backend_internal.h"
  20 #include "frontend_internal.h"
  21
  22 /* Ring buffer backend API */
  23
  24 /* Ring buffer backend access (read/write) */
  25
  26 extern size_t lib_ring_buffer_read(struct lttng_ust_lib_ring_buffer_backend *bufb,
  27                                    size_t offset, void *dest, size_t len,
  28                                    struct lttng_ust_shm_handle *handle)
  29         __attribute__((visibility("hidden")));
  30
  31 extern int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb,
  32                                      size_t offset, void *dest, size_t len,
  33                                      struct lttng_ust_shm_handle *handle)
  34         __attribute__((visibility("hidden")));
  35
  36 /*
  37  * Return the address where a given offset is located.
  38  * Should be used to get the current subbuffer header pointer. Given we know
  39  * it's never on a page boundary, it's safe to write directly to this address,
  40  * as long as the write is never bigger than a page size.
  41  */
  42 extern void *
  43 lib_ring_buffer_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
  44                                size_t offset,
  45                                struct lttng_ust_shm_handle *handle)
  46         __attribute__((visibility("hidden")));
  47
  48 extern void *
  49 lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
  50                                     size_t offset,
  51                                     struct lttng_ust_shm_handle *handle)
  52         __attribute__((visibility("hidden")));
  53
  54 /**
  55  * lib_ring_buffer_write - write data to a buffer backend
  56  * @config : ring buffer instance configuration
  57  * @ctx: ring buffer context. (input arguments only)
  58  * @src : source pointer to copy from
  59  * @len : length of data to copy
  60  *
  61  * This function copies "len" bytes of data from a source pointer to a buffer
  62  * backend, at the current context offset. This is more or less a buffer
  63  * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
  64  * if copy is crossing a page boundary.
  65  */
  66 static inline
  67 void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config,
  68                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
  69                            const void *src, size_t len)
  70         __attribute__((always_inline));
  71 static inline
  72 void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config,
  73                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
  74                            const void *src, size_t len)
  75 {
  76         struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
  77         struct channel_backend *chanb = &ctx_private->chan->backend;
  78         struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
  79         size_t offset = ctx_private->buf_offset;
  80         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
  81         void *p;
  82
  83         if (caa_unlikely(!len))
  84                 return;
  85         /*
  86          * Underlying layer should never ask for writes across
  87          * subbuffers.
  88          */
  89         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
  90         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
  91         if (caa_unlikely(!backend_pages)) {
  92                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
  93                         return;
  94         }
  95         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
  96         if (caa_unlikely(!p))
  97                 return;
  98         lib_ring_buffer_do_copy(config, p, src, len);
  99         ctx_private->buf_offset += len;
 100 }
 101
 102 /*
 103  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 104  * terminating character is found in @src. Returns the number of bytes
 105  * copied. Does *not* terminate @dest with NULL terminating character.
 106  */
 107 static inline
 108 size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 109                 char *dest, const char *src, size_t len)
 110         __attribute__((always_inline));
 111 static inline
 112 size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 113                 char *dest, const char *src, size_t len)
 114 {
 115         size_t count;
 116
 117         for (count = 0; count < len; count++) {
 118                 char c;
 119
 120                 /*
 121                  * Only read source character once, in case it is
 122                  * modified concurrently.
 123                  */
 124                 c = CMM_LOAD_SHARED(src[count]);
 125                 if (!c)
 126                         break;
 127                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 128         }
 129         return count;
 130 }
 131
 132 /**
 133  * lib_ring_buffer_strcpy - write string data to a buffer backend
 134  * @config : ring buffer instance configuration
 135  * @ctx: ring buffer context. (input arguments only)
 136  * @src : source pointer to copy from
 137  * @len : length of data to copy
 138  * @pad : character to use for padding
 139  *
 140  * This function copies @len - 1 bytes of string data from a source
 141  * pointer to a buffer backend, followed by a terminating '\0'
 142  * character, at the current context offset. This is more or less a
 143  * buffer backend-specific strncpy() operation. If a terminating '\0'
 144  * character is found in @src before @len - 1 characters are copied, pad
 145  * the buffer with @pad characters (e.g. '#').
 146  */
 147 static inline
 148 void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 149                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 150                            const char *src, size_t len, char pad)
 151         __attribute__((always_inline));
 152 static inline
 153 void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 154                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 155                            const char *src, size_t len, char pad)
 156 {
 157         struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
 158         struct channel_backend *chanb = &ctx_private->chan->backend;
 159         struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
 160         size_t count;
 161         size_t offset = ctx_private->buf_offset;
 162         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 163         void *p;
 164
 165         if (caa_unlikely(!len))
 166                 return;
 167         /*
 168          * Underlying layer should never ask for writes across
 169          * subbuffers.
 170          */
 171         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
 172         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 173         if (caa_unlikely(!backend_pages)) {
 174                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
 175                         return;
 176         }
 177         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 178         if (caa_unlikely(!p))
 179                 return;
 180
 181         count = lib_ring_buffer_do_strcpy(config, p, src, len - 1);
 182         offset += count;
 183         /* Padding */
 184         if (caa_unlikely(count < len - 1)) {
 185                 size_t pad_len = len - 1 - count;
 186
 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, pad, pad_len);
 191                 offset += pad_len;
 192         }
 193         /* Final '\0' */
 194         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 195         if (caa_unlikely(!p))
 196                 return;
 197         lib_ring_buffer_do_memset(p, '\0', 1);
 198         ctx_private->buf_offset += len;
 199 }
 200
 201 /**
 202  * lib_ring_buffer_pstrcpy - write to a buffer backend P-string
 203  * @config : ring buffer instance configuration
 204  * @ctx: ring buffer context. (input arguments only)
 205  * @src : source pointer to copy from
 206  * @len : length of data to copy
 207  * @pad : character to use for padding
 208  *
 209  * This function copies up to @len bytes of data from a source pointer
 210  * to a Pascal String into the buffer backend. If a terminating '\0'
 211  * character is found in @src before @len characters are copied, pad the
 212  * buffer with @pad characters (e.g.  '\0').
 213  *
 214  * The length of the pascal strings in the ring buffer is explicit: it
 215  * is either the array or sequence length.
 216  */
 217 static inline
 218 void lib_ring_buffer_pstrcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 219                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 220                            const char *src, size_t len, char pad)
 221         __attribute__((always_inline));
 222 static inline
 223 void lib_ring_buffer_pstrcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 224                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 225                            const char *src, size_t len, char pad)
 226 {
 227         struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
 228         struct channel_backend *chanb = &ctx_private->chan->backend;
 229         struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
 230         size_t count;
 231         size_t offset = ctx_private->buf_offset;
 232         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 233         void *p;
 234
 235         if (caa_unlikely(!len))
 236                 return;
 237         /*
 238          * Underlying layer should never ask for writes across
 239          * subbuffers.
 240          */
 241         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
 242         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 243         if (caa_unlikely(!backend_pages)) {
 244                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
 245                         return;
 246         }
 247         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 248         if (caa_unlikely(!p))
 249                 return;
 250
 251         count = lib_ring_buffer_do_strcpy(config, p, src, len);
 252         offset += count;
 253         /* Padding */
 254         if (caa_unlikely(count < len)) {
 255                 size_t pad_len = len - count;
 256
 257                 p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 258                 if (caa_unlikely(!p))
 259                         return;
 260                 lib_ring_buffer_do_memset(p, pad, pad_len);
 261         }
 262         ctx_private->buf_offset += len;
 263 }
 264
 265 /*
 266  * This accessor counts the number of unread records in a buffer.
 267  * It only provides a consistent value if no reads not writes are performed
 268  * concurrently.
 269  */
 270 static inline
 271 unsigned long lib_ring_buffer_get_records_unread(
 272                                 const struct lttng_ust_lib_ring_buffer_config *config,
 273                                 struct lttng_ust_lib_ring_buffer *buf,
 274                                 struct lttng_ust_shm_handle *handle)
 275 {
 276         struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
 277         unsigned long records_unread = 0, sb_bindex;
 278         unsigned int i;
 279         struct lttng_ust_lib_ring_buffer_channel *chan;
 280
 281         chan = shmp(handle, bufb->chan);
 282         if (!chan)
 283                 return 0;
 284         for (i = 0; i < chan->backend.num_subbuf; i++) {
 285                 struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 286                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 287                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 288
 289                 wsb = shmp_index(handle, bufb->buf_wsb, i);
 290                 if (!wsb)
 291                         return 0;
 292                 sb_bindex = subbuffer_id_get_index(config, wsb->id);
 293                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 294                 if (!rpages)
 295                         return 0;
 296                 backend_pages = shmp(handle, rpages->shmp);
 297                 if (!backend_pages)
 298                         return 0;
 299                 records_unread += v_read(config, &backend_pages->records_unread);
 300         }
 301         if (config->mode == RING_BUFFER_OVERWRITE) {
 302                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 303                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 304
 305                 sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 306                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 307                 if (!rpages)
 308                         return 0;
 309                 backend_pages = shmp(handle, rpages->shmp);
 310                 if (!backend_pages)
 311                         return 0;
 312                 records_unread += v_read(config, &backend_pages->records_unread);
 313         }
 314         return records_unread;
 315 }
 316
 317 #endif /* _LTTNG_RING_BUFFER_BACKEND_H */