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 /* Internal helpers */
  18 #include "backend_internal.h"
  19 #include "frontend_internal.h"
  20
  21 /* Ring buffer backend API */
  22
  23 /* Ring buffer backend access (read/write) */
  24
  25 extern size_t lib_ring_buffer_read(struct lib_ring_buffer_backend *bufb,
  26                                    size_t offset, void *dest, size_t len);
  27
  28 extern int __lib_ring_buffer_copy_to_user(struct lib_ring_buffer_backend *bufb,
  29                                           size_t offset, void __user *dest,
  30                                           size_t len);
  31
  32 extern int lib_ring_buffer_read_cstr(struct lib_ring_buffer_backend *bufb,
  33                                      size_t offset, void *dest, size_t len);
  34
  35 extern struct page **
  36 lib_ring_buffer_read_get_page(struct lib_ring_buffer_backend *bufb, size_t offset,
  37                               void ***virt);
  38
  39 /*
  40  * Return the address where a given offset is located.
  41  * Should be used to get the current subbuffer header pointer. Given we know
  42  * it's never on a page boundary, it's safe to write directly to this address,
  43  * as long as the write is never bigger than a page size.
  44  */
  45 extern void *
  46 lib_ring_buffer_offset_address(struct lib_ring_buffer_backend *bufb,
  47                                size_t offset);
  48 extern void *
  49 lib_ring_buffer_read_offset_address(struct lib_ring_buffer_backend *bufb,
  50                                     size_t offset);
  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         size_t sbidx, index;
  72         size_t offset = ctx->buf_offset;
  73         ssize_t pagecpy;
  74         struct lib_ring_buffer_backend_pages *rpages;
  75         unsigned long sb_bindex, id;
  76
  77         offset &= chanb->buf_size - 1;
  78         sbidx = offset >> chanb->subbuf_size_order;
  79         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
  80         pagecpy = min_t(size_t, len, (-offset) & ~PAGE_MASK);
  81         id = bufb->buf_wsb[sbidx].id;
  82         sb_bindex = subbuffer_id_get_index(config, id);
  83         rpages = bufb->array[sb_bindex];
  84         CHAN_WARN_ON(ctx->chan,
  85                      config->mode == RING_BUFFER_OVERWRITE
  86                      && subbuffer_id_is_noref(config, id));
  87         if (likely(pagecpy == len))
  88                 lib_ring_buffer_do_copy(config,
  89                                         rpages->p[index].virt
  90                                             + (offset & ~PAGE_MASK),
  91                                         src, len);
  92         else
  93                 _lib_ring_buffer_write(bufb, offset, src, len, 0);
  94         ctx->buf_offset += len;
  95 }
  96
  97 /*
  98  * This accessor counts the number of unread records in a buffer.
  99  * It only provides a consistent value if no reads not writes are performed
 100  * concurrently.
 101  */
 102 static inline
 103 unsigned long lib_ring_buffer_get_records_unread(
 104                                 const struct lib_ring_buffer_config *config,
 105                                 struct lib_ring_buffer *buf)
 106 {
 107         struct lib_ring_buffer_backend *bufb = &buf->backend;
 108         struct lib_ring_buffer_backend_pages *pages;
 109         unsigned long records_unread = 0, sb_bindex, id;
 110         unsigned int i;
 111
 112         for (i = 0; i < bufb->chan->backend.num_subbuf; i++) {
 113                 id = bufb->buf_wsb[i].id;
 114                 sb_bindex = subbuffer_id_get_index(config, id);
 115                 pages = bufb->array[sb_bindex];
 116                 records_unread += v_read(config, &pages->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 = bufb->array[sb_bindex];
 122                 records_unread += v_read(config, &pages->records_unread);
 123         }
 124         return records_unread;
 125 }
 126
 127 ssize_t lib_ring_buffer_file_splice_read(struct file *in, loff_t *ppos,
 128                                          struct pipe_inode_info *pipe,
 129                                          size_t len, unsigned int flags);
 130 loff_t lib_ring_buffer_no_llseek(struct file *file, loff_t offset, int origin);
 131
 132 #endif /* _LINUX_RING_BUFFER_BACKEND_H */