ustd/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 <assert.h>
  19 #include <byteswap.h>
  20
  21 #include "buffers.h"
  22 #include "tracer.h"
  23 #include "ustd.h"
  24 #include "usterr.h"
  25
  26 /* This truncates to an offset in the buffer. */
  27 #define USTD_BUFFER_TRUNC(offset, bufinfo) \
  28         ((offset) & (~(((bufinfo)->subbuf_size*(bufinfo)->n_subbufs)-1)))
  29
  30 #define LTT_MAGIC_NUMBER 0x00D6B7ED
  31 #define LTT_REV_MAGIC_NUMBER 0xEDB7D600
  32
  33 /* Returns the size of a subbuffer size. This is the size that
  34  * will need to be written to disk.
  35  *
  36  * @subbuffer: pointer to the beginning of the subbuffer (the
  37  *             beginning of its header)
  38  */
  39
  40 size_t subbuffer_data_size(void *subbuf)
  41 {
  42         struct ltt_subbuffer_header *header = subbuf;
  43         int reverse;
  44         u32 data_size;
  45
  46         if(header->magic_number == LTT_MAGIC_NUMBER) {
  47                 reverse = 0;
  48         }
  49         else if(header->magic_number == LTT_REV_MAGIC_NUMBER) {
  50                 reverse = 1;
  51         }
  52         else {
  53                 return -1;
  54         }
  55
  56         data_size = header->sb_size;
  57         if(reverse)
  58                 data_size = bswap_32(data_size);
  59
  60         return data_size;
  61 }
  62
  63
  64 void finish_consuming_dead_subbuffer(struct buffer_info *buf)
  65 {
  66         struct ust_buffer *ustbuf = buf->bufstruct_mem;
  67
  68         long write_offset = uatomic_read(&ustbuf->offset);
  69         long consumed_offset = uatomic_read(&ustbuf->consumed);
  70
  71         long i_subbuf;
  72
  73         DBG("processing dead buffer (%s)", buf->name);
  74         DBG("consumed offset is %ld (%s)", consumed_offset, buf->name);
  75         DBG("write offset is %ld (%s)", write_offset, buf->name);
  76
  77         /* First subbuf that we need to consume now. It is not modulo'd.
  78          * Consumed_offset is the next byte to consume.  */
  79         long first_subbuf = consumed_offset / buf->subbuf_size;
  80         /* Last subbuf that we need to consume now. It is not modulo'd.
  81          * Write_offset is the next place to write so write_offset-1 is the
  82          * last place written. */
  83         long last_subbuf = (write_offset - 1) / buf->subbuf_size;
  84
  85         DBG("first_subbuf=%ld", first_subbuf);
  86         DBG("last_subbuf=%ld", last_subbuf);
  87
  88         if(last_subbuf - first_subbuf >= buf->n_subbufs) {
  89                 DBG("an overflow has occurred, nothing can be recovered");
  90                 return;
  91         }
  92
  93         /* Iterate on subbuffers to recover. */
  94         for(i_subbuf = first_subbuf % buf->n_subbufs; ; i_subbuf++, i_subbuf %= buf->n_subbufs) {
  95                 void *tmp;
  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                 int pad_size;
 107
 108                 if((commit_seq & commit_seq_mask) == 0) {
 109                         /* There is nothing to do. */
 110                         /* FIXME: is this needed? */
 111                         break;
 112                 }
 113
 114                 /* Check if subbuf was fully written. This is from Mathieu's algorithm/paper. */
 115                 /* FIXME: not sure data_size = 0xffffffff when the buffer is not full. It might
 116                  * take the value of the header size initially */
 117                 if (((commit_seq - buf->subbuf_size) & commit_seq_mask)
 118                     - (USTD_BUFFER_TRUNC(consumed_offset, buf) >> n_subbufs_order) == 0
 119                     && header->data_size != 0xffffffff && header->sb_size != 0xffffffff) {
 120                         /* If it was, we only check the data_size. This is the amount of valid data at
 121                          * the beginning of the subbuffer. */
 122                         valid_length = header->data_size;
 123                         DBG("writing full subbuffer (%d) with valid_length = %ld", i_subbuf, valid_length);
 124                 }
 125                 else {
 126                         /* If the subbuffer was not fully written, then we don't check data_size because
 127                          * it hasn't been written yet. Instead we check commit_seq and use it to choose
 128                          * a value for data_size. The viewer will need this value when parsing.
 129                          */
 130
 131                         valid_length = commit_seq & (buf->subbuf_size-1);
 132                         DBG("writing unfull subbuffer (%d) with valid_length = %ld", i_subbuf, valid_length);
 133                         header->data_size = valid_length;
 134                         header->sb_size = PAGE_ALIGN(valid_length);
 135                         assert(i_subbuf == (last_subbuf % buf->n_subbufs));
 136                 }
 137
 138
 139                 patient_write(buf->file_fd, buf->mem + i_subbuf * buf->subbuf_size, valid_length);
 140
 141                 /* pad with empty bytes */
 142                 pad_size = PAGE_ALIGN(valid_length)-valid_length;
 143                 if(pad_size) {
 144                         tmp = malloc(pad_size);
 145                         memset(tmp, 0, pad_size);
 146                         patient_write(buf->file_fd, tmp, pad_size);
 147                         free(tmp);
 148                 }
 149
 150                 if(i_subbuf == last_subbuf % buf->n_subbufs)
 151                         break;
 152         }
 153 }
 154