libustd/lowlevel.c

   1 /* Copyright (C) 2009  Pierre-Marc Fournier
   2  *
   3  * This library is free software; you can redistribute it and/or
   4  * modify it under the terms of the GNU Lesser General Public
   5  * License as published by the Free Software Foundation; either
   6  * version 2.1 of the License, or (at your option) any later version.
   7  *
   8  * This library is distributed in the hope that it will be useful,
   9  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * Lesser General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public
  14  * License along with this library; if not, write to the Free Software
  15  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
  16  */
  17
  18 #include <stdlib.h>
  19 #include <assert.h>
  20 #include <byteswap.h>
  21
  22 #include "buffers.h"
  23 #include "tracer.h"
  24 #include "libustd.h"
  25 #include "usterr.h"
  26
  27 /* This truncates to an offset in the buffer. */
  28 #define USTD_BUFFER_TRUNC(offset, bufinfo) \
  29         ((offset) & (~(((bufinfo)->subbuf_size*(bufinfo)->n_subbufs)-1)))
  30
  31 #define LTT_MAGIC_NUMBER 0x00D6B7ED
  32 #define LTT_REV_MAGIC_NUMBER 0xEDB7D600
  33
  34 /* Returns the size of a subbuffer size. This is the size that
  35  * will need to be written to disk.
  36  *
  37  * @subbuffer: pointer to the beginning of the subbuffer (the
  38  *             beginning of its header)
  39  */
  40
  41 size_t subbuffer_data_size(void *subbuf)
  42 {
  43         struct ltt_subbuffer_header *header = subbuf;
  44         int reverse;
  45         u32 data_size;
  46
  47         if(header->magic_number == LTT_MAGIC_NUMBER) {
  48                 reverse = 0;
  49         }
  50         else if(header->magic_number == LTT_REV_MAGIC_NUMBER) {
  51                 reverse = 1;
  52         }
  53         else {
  54                 return -1;
  55         }
  56
  57         data_size = header->sb_size;
  58         if(reverse)
  59                 data_size = bswap_32(data_size);
  60
  61         return data_size;
  62 }
  63
  64
  65 void finish_consuming_dead_subbuffer(struct libustd_callbacks *callbacks, struct buffer_info *buf)
  66 {
  67         struct ust_buffer *ustbuf = buf->bufstruct_mem;
  68
  69         long write_offset = uatomic_read(&ustbuf->offset);
  70         long consumed_offset = uatomic_read(&ustbuf->consumed);
  71
  72         long i_subbuf;
  73
  74         DBG("processing dead buffer (%s)", buf->name);
  75         DBG("consumed offset is %ld (%s)", consumed_offset, buf->name);
  76         DBG("write offset is %ld (%s)", write_offset, buf->name);
  77
  78         /* First subbuf that we need to consume now. It is not modulo'd.
  79          * Consumed_offset is the next byte to consume.  */
  80         long first_subbuf = consumed_offset / buf->subbuf_size;
  81         /* Last subbuf that we need to consume now. It is not modulo'd.
  82          * Write_offset is the next place to write so write_offset-1 is the
  83          * last place written. */
  84         long last_subbuf = (write_offset - 1) / buf->subbuf_size;
  85
  86         DBG("first_subbuf=%ld", first_subbuf);
  87         DBG("last_subbuf=%ld", last_subbuf);
  88
  89         if(last_subbuf - first_subbuf >= buf->n_subbufs) {
  90                 DBG("an overflow has occurred, nothing can be recovered");
  91                 return;
  92         }
  93
  94         /* Iterate on subbuffers to recover. */
  95         for(i_subbuf = first_subbuf % buf->n_subbufs; ; i_subbuf++, i_subbuf %= buf->n_subbufs) {
  96                 /* commit_seq is the offset in the buffer of the end of the last sequential commit.
  97                  * Bytes beyond this limit cannot be recovered. This is a free-running counter. */
  98                 long commit_seq = uatomic_read(&ustbuf->commit_seq[i_subbuf]);
  99
 100                 unsigned long valid_length = buf->subbuf_size;
 101                 long n_subbufs_order = get_count_order(buf->n_subbufs);
 102                 long commit_seq_mask = (~0UL >> n_subbufs_order);
 103
 104                 struct ltt_subbuffer_header *header = (struct ltt_subbuffer_header *)((char *)buf->mem+i_subbuf*buf->subbuf_size);
 105
 106                 if((commit_seq & commit_seq_mask) == 0) {
 107                         /* There is nothing to do. */
 108                         /* FIXME: is this needed? */
 109                         break;
 110                 }
 111
 112                 /* Check if subbuf was fully written. This is from Mathieu's algorithm/paper. */
 113                 /* FIXME: not sure data_size = 0xffffffff when the buffer is not full. It might
 114                  * take the value of the header size initially */
 115                 if (((commit_seq - buf->subbuf_size) & commit_seq_mask)
 116                     - (USTD_BUFFER_TRUNC(consumed_offset, buf) >> n_subbufs_order) == 0
 117                     && header->data_size != 0xffffffff && header->sb_size != 0xffffffff) {
 118                         /* If it was, we only check the data_size. This is the amount of valid data at
 119                          * the beginning of the subbuffer. */
 120                         valid_length = header->data_size;
 121                         DBG("writing full subbuffer (%d) with valid_length = %ld", i_subbuf, valid_length);
 122                 }
 123                 else {
 124                         /* If the subbuffer was not fully written, then we don't check data_size because
 125                          * it hasn't been written yet. Instead we check commit_seq and use it to choose
 126                          * a value for data_size. The viewer will need this value when parsing.
 127                          */
 128
 129                         valid_length = commit_seq & (buf->subbuf_size-1);
 130                         DBG("writing unfull subbuffer (%d) with valid_length = %ld", i_subbuf, valid_length);
 131                         header->data_size = valid_length;
 132                         header->sb_size = PAGE_ALIGN(valid_length);
 133                         assert(i_subbuf == (last_subbuf % buf->n_subbufs));
 134                 }
 135
 136                 if(callbacks->on_read_partial_subbuffer)
 137                         callbacks->on_read_partial_subbuffer(callbacks, buf, i_subbuf, valid_length);
 138
 139                 if(i_subbuf == last_subbuf % buf->n_subbufs)
 140                         break;
 141         }
 142 }
 143