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