libringbuffer/backend.h

   1 #ifndef _LINUX_RING_BUFFER_BACKEND_H
   2 #define _LINUX_RING_BUFFER_BACKEND_H
   3
   4 /*
   5  * linux/ringbuffer/backend.h
   6  *
   7  * Copyright (C) 2008-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * Ring buffer backend (API).
  10  *
  11  * Dual LGPL v2.1/GPL v2 license.
  12  *
  13  * Credits to Steven Rostedt for proposing to use an extra-subbuffer owned by
  14  * the reader in flight recorder mode.
  15  */
  16
  17 #include <unistd.h>
  18
  19 #include "ust/core.h"
  20
  21 /* Internal helpers */
  22 #include "backend_internal.h"
  23 #include "frontend_internal.h"
  24
  25 /* Ring buffer backend API */
  26
  27 /* Ring buffer backend access (read/write) */
  28
  29 extern size_t lib_ring_buffer_read(struct lib_ring_buffer_backend *bufb,
  30                                    size_t offset, void *dest, size_t len,
  31                                    struct lttng_ust_shm_handle *handle);
  32
  33 extern int lib_ring_buffer_read_cstr(struct lib_ring_buffer_backend *bufb,
  34                                      size_t offset, void *dest, size_t len,
  35                                      struct lttng_ust_shm_handle *handle);
  36
  37 /*
  38  * Return the address where a given offset is located.
  39  * Should be used to get the current subbuffer header pointer. Given we know
  40  * it's never on a page boundary, it's safe to write directly to this address,
  41  * as long as the write is never bigger than a page size.
  42  */
  43 extern void *
  44 lib_ring_buffer_offset_address(struct lib_ring_buffer_backend *bufb,
  45                                size_t offset,
  46                                struct lttng_ust_shm_handle *handle);
  47 extern void *
  48 lib_ring_buffer_read_offset_address(struct lib_ring_buffer_backend *bufb,
  49                                     size_t offset,
  50                                     struct lttng_ust_shm_handle *handle);
  51
  52 /**
  53  * lib_ring_buffer_write - write data to a buffer backend
  54  * @config : ring buffer instance configuration
  55  * @ctx: ring buffer context. (input arguments only)
  56  * @src : source pointer to copy from
  57  * @len : length of data to copy
  58  *
  59  * This function copies "len" bytes of data from a source pointer to a buffer
  60  * backend, at the current context offset. This is more or less a buffer
  61  * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
  62  * if copy is crossing a page boundary.
  63  */
  64 static inline
  65 void lib_ring_buffer_write(const struct lib_ring_buffer_config *config,
  66                            struct lib_ring_buffer_ctx *ctx,
  67                            const void *src, size_t len)
  68 {
  69         struct lib_ring_buffer_backend *bufb = &ctx->buf->backend;
  70         struct channel_backend *chanb = &ctx->chan->backend;
  71         struct lttng_ust_shm_handle *handle = ctx->handle;
  72         size_t sbidx;
  73         size_t offset = ctx->buf_offset;
  74         struct lib_ring_buffer_backend_pages_shmp *rpages;
  75         unsigned long sb_bindex, id;
  76
  77         offset &= chanb->buf_size - 1;
  78         sbidx = offset >> chanb->subbuf_size_order;
  79         id = shmp_index(handle, bufb->buf_wsb, sbidx)->id;
  80         sb_bindex = subbuffer_id_get_index(config, id);
  81         rpages = shmp_index(handle, bufb->array, sb_bindex);
  82         CHAN_WARN_ON(ctx->chan,
  83                      config->mode == RING_BUFFER_OVERWRITE
  84                      && subbuffer_id_is_noref(config, id));
  85         /*
  86          * Underlying layer should never ask for writes across
  87          * subbuffers.
  88          */
  89         CHAN_WARN_ON(chanb, offset >= chanb->buf_size);
  90         lib_ring_buffer_do_copy(config,
  91                                 shmp_index(handle, shmp(handle, rpages->shmp)->p, offset & (chanb->subbuf_size - 1)),
  92                                 src, len);
  93         ctx->buf_offset += len;
  94 }
  95
  96 /*
  97  * This accessor counts the number of unread records in a buffer.
  98  * It only provides a consistent value if no reads not writes are performed
  99  * concurrently.
 100  */
 101 static inline
 102 unsigned long lib_ring_buffer_get_records_unread(
 103                                 const struct lib_ring_buffer_config *config,
 104                                 struct lib_ring_buffer *buf,
 105                                 struct lttng_ust_shm_handle *handle)
 106 {
 107         struct lib_ring_buffer_backend *bufb = &buf->backend;
 108         struct lib_ring_buffer_backend_pages_shmp *pages;
 109         unsigned long records_unread = 0, sb_bindex, id;
 110         unsigned int i;
 111
 112         for (i = 0; i < shmp(handle, bufb->chan)->backend.num_subbuf; i++) {
 113                 id = shmp_index(handle, bufb->buf_wsb, i)->id;
 114                 sb_bindex = subbuffer_id_get_index(config, id);
 115                 pages = shmp_index(handle, bufb->array, sb_bindex);
 116                 records_unread += v_read(config, &shmp(handle, pages->shmp)->records_unread);
 117         }
 118         if (config->mode == RING_BUFFER_OVERWRITE) {
 119                 id = bufb->buf_rsb.id;
 120                 sb_bindex = subbuffer_id_get_index(config, id);
 121                 pages = shmp_index(handle, bufb->array, sb_bindex);
 122                 records_unread += v_read(config, &shmp(handle, pages->shmp)->records_unread);
 123         }
 124         return records_unread;
 125 }
 126
 127 #endif /* _LINUX_RING_BUFFER_BACKEND_H */