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dmg: drop broken bdrv_pread() loop 

It is not necessary to check errno for EINTR and the block layer does
not produce short reads.  Therefore we can drop the loop that attempts
to read a compressed chunk.

The loop is buggy because it incorrectly adds the transferred bytes
twice:

  do {
      ret = bdrv_pread(...);
      i += ret;
  } while (ret >= 0 && ret + i < s->lengths[chunk]);

Luckily we can drop the loop completely and perform a single
bdrv_pread().

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
(cherry picked from commit b404bf8542)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
This commit is contained in:
Stefan Hajnoczi 2014-03-26 13:05:56 +01:00 committed by Michael Roth
parent ad08cae75c
commit 4ee5b9c8cb
1 changed files with 2 additions and 13 deletions
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15
block/dmg.c
View File

@ -298,21 +298,10 @@ static inline int dmg_read_chunk(BlockDriverState *bs, int sector_num)
s->current_chunk = s->n_chunks;
switch (s->types[chunk]) {
case 0x80000005: { /* zlib compressed */
int i;
/* we need to buffer, because only the chunk as whole can be
* inflated. */
i = 0;
do {
ret = bdrv_pread(bs->file, s->offsets[chunk] + i,
s->compressed_chunk + i,
s->lengths[chunk] - i);
if (ret < 0 && errno == EINTR) {
ret = 0;
}
i += ret;
} while (ret >= 0 && ret + i < s->lengths[chunk]);
ret = bdrv_pread(bs->file, s->offsets[chunk],
s->compressed_chunk, s->lengths[chunk]);
if (ret != s->lengths[chunk]) {
return -1;
}