src/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(
 113                 const struct lttng_ust_lib_ring_buffer_config *config  __attribute__((unused)),
 114                 char *dest, const char *src, size_t len)
 115 {
 116         size_t count;
 117
 118         for (count = 0; count < len; count++) {
 119                 char c;
 120
 121                 /*
 122                  * Only read source character once, in case it is
 123                  * modified concurrently.
 124                  */
 125                 c = CMM_LOAD_SHARED(src[count]);
 126                 if (!c)
 127                         break;
 128                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 129         }
 130         return count;
 131 }
 132
 133 /**
 134  * lib_ring_buffer_strcpy - write string data to a buffer backend
 135  * @config : ring buffer instance configuration
 136  * @ctx: ring buffer context. (input arguments only)
 137  * @src : source pointer to copy from
 138  * @len : length of data to copy
 139  * @pad : character to use for padding
 140  *
 141  * This function copies @len - 1 bytes of string data from a source
 142  * pointer to a buffer backend, followed by a terminating '\0'
 143  * character, at the current context offset. This is more or less a
 144  * buffer backend-specific strncpy() operation. If a terminating '\0'
 145  * character is found in @src before @len - 1 characters are copied, pad
 146  * the buffer with @pad characters (e.g. '#').
 147  */
 148 static inline
 149 void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 150                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 151                            const char *src, size_t len, char pad)
 152         __attribute__((always_inline));
 153 static inline
 154 void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 155                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 156                            const char *src, size_t len, char pad)
 157 {
 158         struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
 159         struct channel_backend *chanb = &ctx_private->chan->backend;
 160         struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
 161         size_t count;
 162         size_t offset = ctx_private->buf_offset;
 163         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 164         void *p;
 165
 166         if (caa_unlikely(!len))
 167                 return;
 168         /*
 169          * Underlying layer should never ask for writes across
 170          * subbuffers.
 171          */
 172         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
 173         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 174         if (caa_unlikely(!backend_pages)) {
 175                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
 176                         return;
 177         }
 178         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 179         if (caa_unlikely(!p))
 180                 return;
 181
 182         count = lib_ring_buffer_do_strcpy(config, p, src, len - 1);
 183         offset += count;
 184         /* Padding */
 185         if (caa_unlikely(count < len - 1)) {
 186                 size_t pad_len = len - 1 - count;
 187
 188                 p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 189                 if (caa_unlikely(!p))
 190                         return;
 191                 lib_ring_buffer_do_memset(p, pad, pad_len);
 192                 offset += pad_len;
 193         }
 194         /* Final '\0' */
 195         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 196         if (caa_unlikely(!p))
 197                 return;
 198         lib_ring_buffer_do_memset(p, '\0', 1);
 199         ctx_private->buf_offset += len;
 200 }
 201
 202 /**
 203  * lib_ring_buffer_pstrcpy - write to a buffer backend P-string
 204  * @config : ring buffer instance configuration
 205  * @ctx: ring buffer context. (input arguments only)
 206  * @src : source pointer to copy from
 207  * @len : length of data to copy
 208  * @pad : character to use for padding
 209  *
 210  * This function copies up to @len bytes of data from a source pointer
 211  * to a Pascal String into the buffer backend. If a terminating '\0'
 212  * character is found in @src before @len characters are copied, pad the
 213  * buffer with @pad characters (e.g.  '\0').
 214  *
 215  * The length of the pascal strings in the ring buffer is explicit: it
 216  * is either the array or sequence length.
 217  */
 218 static inline
 219 void lib_ring_buffer_pstrcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 220                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 221                            const char *src, size_t len, char pad)
 222         __attribute__((always_inline));
 223 static inline
 224 void lib_ring_buffer_pstrcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 225                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 226                            const char *src, size_t len, char pad)
 227 {
 228         struct lttng_ust_lib_ring_buffer_ctx_private *ctx_private = ctx->priv;
 229         struct channel_backend *chanb = &ctx_private->chan->backend;
 230         struct lttng_ust_shm_handle *handle = ctx_private->chan->handle;
 231         size_t count;
 232         size_t offset = ctx_private->buf_offset;
 233         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 234         void *p;
 235
 236         if (caa_unlikely(!len))
 237                 return;
 238         /*
 239          * Underlying layer should never ask for writes across
 240          * subbuffers.
 241          */
 242         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
 243         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 244         if (caa_unlikely(!backend_pages)) {
 245                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
 246                         return;
 247         }
 248         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 249         if (caa_unlikely(!p))
 250                 return;
 251
 252         count = lib_ring_buffer_do_strcpy(config, p, src, len);
 253         offset += count;
 254         /* Padding */
 255         if (caa_unlikely(count < len)) {
 256                 size_t pad_len = len - count;
 257
 258                 p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 259                 if (caa_unlikely(!p))
 260                         return;
 261                 lib_ring_buffer_do_memset(p, pad, pad_len);
 262         }
 263         ctx_private->buf_offset += len;
 264 }
 265
 266 /*
 267  * This accessor counts the number of unread records in a buffer.
 268  * It only provides a consistent value if no reads not writes are performed
 269  * concurrently.
 270  */
 271 static inline
 272 unsigned long lib_ring_buffer_get_records_unread(
 273                                 const struct lttng_ust_lib_ring_buffer_config *config,
 274                                 struct lttng_ust_lib_ring_buffer *buf,
 275                                 struct lttng_ust_shm_handle *handle)
 276 {
 277         struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
 278         unsigned long records_unread = 0, sb_bindex;
 279         unsigned int i;
 280         struct lttng_ust_lib_ring_buffer_channel *chan;
 281
 282         chan = shmp(handle, bufb->chan);
 283         if (!chan)
 284                 return 0;
 285         for (i = 0; i < chan->backend.num_subbuf; i++) {
 286                 struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 287                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 288                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 289
 290                 wsb = shmp_index(handle, bufb->buf_wsb, i);
 291                 if (!wsb)
 292                         return 0;
 293                 sb_bindex = subbuffer_id_get_index(config, wsb->id);
 294                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 295                 if (!rpages)
 296                         return 0;
 297                 backend_pages = shmp(handle, rpages->shmp);
 298                 if (!backend_pages)
 299                         return 0;
 300                 records_unread += v_read(config, &backend_pages->records_unread);
 301         }
 302         if (config->mode == RING_BUFFER_OVERWRITE) {
 303                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 304                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 305
 306                 sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.id);
 307                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 308                 if (!rpages)
 309                         return 0;
 310                 backend_pages = shmp(handle, rpages->shmp);
 311                 if (!backend_pages)
 312                         return 0;
 313                 records_unread += v_read(config, &backend_pages->records_unread);
 314         }
 315         return records_unread;
 316 }
 317
 318 #endif /* _LTTNG_RING_BUFFER_BACKEND_H */