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
  30 extern int lib_ring_buffer_read_cstr(struct lttng_ust_lib_ring_buffer_backend *bufb,
  31                                      size_t offset, void *dest, size_t len,
  32                                      struct lttng_ust_shm_handle *handle);
  33
  34 /*
  35  * Return the address where a given offset is located.
  36  * Should be used to get the current subbuffer header pointer. Given we know
  37  * it's never on a page boundary, it's safe to write directly to this address,
  38  * as long as the write is never bigger than a page size.
  39  */
  40 extern void *
  41 lib_ring_buffer_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
  42                                size_t offset,
  43                                struct lttng_ust_shm_handle *handle);
  44 extern void *
  45 lib_ring_buffer_read_offset_address(struct lttng_ust_lib_ring_buffer_backend *bufb,
  46                                     size_t offset,
  47                                     struct lttng_ust_shm_handle *handle);
  48
  49 /**
  50  * lib_ring_buffer_write - write data to a buffer backend
  51  * @config : ring buffer instance configuration
  52  * @ctx: ring buffer context. (input arguments only)
  53  * @src : source pointer to copy from
  54  * @len : length of data to copy
  55  *
  56  * This function copies "len" bytes of data from a source pointer to a buffer
  57  * backend, at the current context offset. This is more or less a buffer
  58  * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
  59  * if copy is crossing a page boundary.
  60  */
  61 static inline __attribute__((always_inline))
  62 void lib_ring_buffer_write(const struct lttng_ust_lib_ring_buffer_config *config,
  63                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
  64                            const void *src, size_t len)
  65 {
  66         struct channel_backend *chanb = &ctx->chan->backend;
  67         struct lttng_ust_shm_handle *handle = ctx->handle;
  68         size_t offset = ctx->buf_offset;
  69         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
  70         void *p;
  71
  72         if (caa_unlikely(!len))
  73                 return;
  74         /*
  75          * Underlying layer should never ask for writes across
  76          * subbuffers.
  77          */
  78         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
  79         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
  80         if (caa_unlikely(!backend_pages)) {
  81                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
  82                         return;
  83         }
  84         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
  85         if (caa_unlikely(!p))
  86                 return;
  87         lib_ring_buffer_do_copy(config, p, src, len);
  88         ctx->buf_offset += len;
  89 }
  90
  91 /*
  92  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
  93  * terminating character is found in @src. Returns the number of bytes
  94  * copied. Does *not* terminate @dest with NULL terminating character.
  95  */
  96 static inline __attribute__((always_inline))
  97 size_t lib_ring_buffer_do_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
  98                 char *dest, const char *src, size_t len)
  99 {
 100         size_t count;
 101
 102         for (count = 0; count < len; count++) {
 103                 char c;
 104
 105                 /*
 106                  * Only read source character once, in case it is
 107                  * modified concurrently.
 108                  */
 109                 c = CMM_LOAD_SHARED(src[count]);
 110                 if (!c)
 111                         break;
 112                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 113         }
 114         return count;
 115 }
 116
 117 /**
 118  * lib_ring_buffer_strcpy - write string data to a buffer backend
 119  * @config : ring buffer instance configuration
 120  * @ctx: ring buffer context. (input arguments only)
 121  * @src : source pointer to copy from
 122  * @len : length of data to copy
 123  * @pad : character to use for padding
 124  *
 125  * This function copies @len - 1 bytes of string data from a source
 126  * pointer to a buffer backend, followed by a terminating '\0'
 127  * character, at the current context offset. This is more or less a
 128  * buffer backend-specific strncpy() operation. If a terminating '\0'
 129  * character is found in @src before @len - 1 characters are copied, pad
 130  * the buffer with @pad characters (e.g. '#').
 131  */
 132 static inline __attribute__((always_inline))
 133 void lib_ring_buffer_strcpy(const struct lttng_ust_lib_ring_buffer_config *config,
 134                            struct lttng_ust_lib_ring_buffer_ctx *ctx,
 135                            const char *src, size_t len, int pad)
 136 {
 137         struct channel_backend *chanb = &ctx->chan->backend;
 138         struct lttng_ust_shm_handle *handle = ctx->handle;
 139         size_t count;
 140         size_t offset = ctx->buf_offset;
 141         struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 142         void *p;
 143
 144         if (caa_unlikely(!len))
 145                 return;
 146         /*
 147          * Underlying layer should never ask for writes across
 148          * subbuffers.
 149          */
 150         CHAN_WARN_ON(chanb, (offset & (chanb->buf_size - 1)) + len > chanb->buf_size);
 151         backend_pages = lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 152         if (caa_unlikely(!backend_pages)) {
 153                 if (lib_ring_buffer_backend_get_pages(config, ctx, &backend_pages))
 154                         return;
 155         }
 156         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 157         if (caa_unlikely(!p))
 158                 return;
 159
 160         count = lib_ring_buffer_do_strcpy(config, p, src, len - 1);
 161         offset += count;
 162         /* Padding */
 163         if (caa_unlikely(count < len - 1)) {
 164                 size_t pad_len = len - 1 - count;
 165
 166                 p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 167                 if (caa_unlikely(!p))
 168                         return;
 169                 lib_ring_buffer_do_memset(p, pad, pad_len);
 170                 offset += pad_len;
 171         }
 172         /* Final '\0' */
 173         p = shmp_index(handle, backend_pages->p, offset & (chanb->subbuf_size - 1));
 174         if (caa_unlikely(!p))
 175                 return;
 176         lib_ring_buffer_do_memset(p, '\0', 1);
 177         ctx->buf_offset += len;
 178 }
 179
 180 /*
 181  * This accessor counts the number of unread records in a buffer.
 182  * It only provides a consistent value if no reads not writes are performed
 183  * concurrently.
 184  */
 185 static inline
 186 unsigned long lib_ring_buffer_get_records_unread(
 187                                 const struct lttng_ust_lib_ring_buffer_config *config,
 188                                 struct lttng_ust_lib_ring_buffer *buf,
 189                                 struct lttng_ust_shm_handle *handle)
 190 {
 191         struct lttng_ust_lib_ring_buffer_backend *bufb = &buf->backend;
 192         unsigned long records_unread = 0, sb_bindex;
 193         unsigned int i;
 194         struct channel *chan;
 195
 196         chan = shmp(handle, bufb->chan);
 197         if (!chan)
 198                 return 0;
 199         for (i = 0; i < chan->backend.num_subbuf; i++) {
 200                 struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
 201                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 202                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 203
 204                 wsb = shmp_index(handle, bufb->buf_wsb, i);
 205                 if (!wsb)
 206                         return 0;
 207                 sb_bindex = subbuffer_id_get_index(config, wsb->id);
 208                 rpages = shmp_index(handle, bufb->array, sb_bindex);
 209                 if (!rpages)
 210                         return 0;
 211                 backend_pages = shmp(handle, rpages->shmp);
 212                 if (!backend_pages)
 213                         return 0;
 214                 records_unread += v_read(config, &backend_pages->records_unread);
 215         }
 216         if (config->mode == RING_BUFFER_OVERWRITE) {
 217                 struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
 218                 struct lttng_ust_lib_ring_buffer_backend_pages *backend_pages;
 219
 220                 sb_bindex = subbuffer_id_get_index(config, bufb->buf_rsb.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         return records_unread;
 230 }
 231
 232 #endif /* _LTTNG_RING_BUFFER_BACKEND_H */