ustd/lowlevel.c

   1 #include <assert.h>
   2
   3 #include "tracer.h"
   4 #include "ustd.h"
   5 #include "localerr.h"
   6
   7 /* This truncates to an offset in the buffer. */
   8 #define USTD_BUFFER_TRUNC(offset, bufinfo) \
   9         ((offset) & (~(((bufinfo)->subbuf_size*(bufinfo)->n_subbufs)-1)))
  10
  11 void finish_consuming_dead_subbuffer(struct buffer_info *buf)
  12 {
  13         struct ltt_channel_buf_struct *ltt_buf = buf->bufstruct_mem;
  14
  15         long write_offset = local_read(&ltt_buf->offset);
  16         long consumed_offset = atomic_long_read(&ltt_buf->consumed);
  17
  18         long i_subbuf;
  19
  20         DBG("processing died buffer");
  21         DBG("consumed offset is %ld", consumed_offset);
  22         DBG("write offset is %ld", write_offset);
  23
  24         /* First subbuf that we need to consume now. It is not modulo'd.
  25          * Consumed_offset is the next byte to consume.  */
  26         long first_subbuf = consumed_offset / buf->subbuf_size;
  27         /* Last subbuf that we need to consume now. It is not modulo'd.
  28          * Write_offset is the next place to write so write_offset-1 is the
  29          * last place written. */
  30         long last_subbuf = (write_offset - 1) / buf->subbuf_size;
  31
  32         DBG("first_subbuf=%ld", first_subbuf);
  33         DBG("last_subbuf=%ld", last_subbuf);
  34
  35         if(last_subbuf - first_subbuf >= buf->n_subbufs) {
  36                 DBG("an overflow has occurred, nothing can be recovered");
  37                 return;
  38         }
  39
  40         /* Iterate on subbuffers to recover. */
  41         for(i_subbuf=first_subbuf; ; i_subbuf++, i_subbuf %= buf->n_subbufs) {
  42                 void *tmp;
  43                 /* commit_seq is the offset in the buffer of the end of the last sequential commit.
  44                  * Bytes beyond this limit cannot be recovered. This is a free-running counter. */
  45                 long commit_seq = local_read(&ltt_buf->commit_seq[i_subbuf]);
  46
  47                 unsigned long valid_length = buf->subbuf_size;
  48                 long n_subbufs_order = get_count_order(buf->n_subbufs);
  49                 long commit_seq_mask = (~0UL >> n_subbufs_order);
  50
  51                 struct ltt_subbuffer_header *header = (struct ltt_subbuffer_header *)((char *)buf->mem+i_subbuf*buf->subbuf_size);
  52
  53                 if((commit_seq & commit_seq_mask) == 0) {
  54                         /* There is nothing to do. */
  55                         /* FIXME: is this needed? */
  56                         break;
  57                 }
  58
  59                 /* Check if subbuf was fully written. This is from Mathieu's algorithm/paper. */
  60                 if (((commit_seq - buf->subbuf_size) & commit_seq_mask)
  61                     - (USTD_BUFFER_TRUNC(consumed_offset, buf) >> n_subbufs_order)
  62                     == 0) {
  63                         /* If it was, we only check the lost_size. This is the lost padding at the end of
  64                          * the subbuffer. */
  65                         valid_length = (unsigned long)buf->subbuf_size - header->lost_size;
  66                 }
  67                 else {
  68                         /* If the subbuffer was not fully written, then we don't check lost_size because
  69                          * it hasn't been written yet. Instead we check commit_seq and use it to choose
  70                          * a value for lost_size. The viewer will need this value when parsing.
  71                          */
  72
  73                         valid_length = commit_seq & (buf->subbuf_size-1);
  74                         header->lost_size = buf->subbuf_size-valid_length;
  75                         assert(i_subbuf == (last_subbuf % buf->n_subbufs));
  76                 }
  77
  78
  79                 patient_write(buf->file_fd, buf->mem + i_subbuf * buf->subbuf_size, valid_length);
  80
  81                 /* pad with empty bytes */
  82                 tmp = malloc(buf->subbuf_size-valid_length);
  83                 memset(tmp, 0, buf->subbuf_size-valid_length);
  84                 patient_write(buf->file_fd, tmp, buf->subbuf_size-valid_length);
  85                 free(tmp);
  86
  87                 if(i_subbuf == last_subbuf % buf->n_subbufs)
  88                         break;
  89         }
  90 }
  91