From: Stefan Hajnoczi Date: Wed, 26 Mar 2014 13:05:56 +0100 Subject: [PATCH] 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 Signed-off-by: Kevin Wolf Reviewed-by: Max Reitz Signed-off-by: Stefan Hajnoczi (cherry picked from commit b404bf854217dbe8a5649449eb3ad33777f7d900) --- block/dmg.c | 15 ++------------- 1 file changed, 2 insertions(+), 13 deletions(-) diff --git a/block/dmg.c b/block/dmg.c index cb4060c..24f08ef 100644 --- a/block/dmg.c +++ b/block/dmg.c @@ -297,21 +297,10 @@ 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; }