There are no needs to allocate more than one cluster, as we set avail_out for deflate to one cluster.
Zlib docs (http://www.zlib.net/manual.html) says: "deflate compresses as much data as possible, and stops when the input buffer becomes empty or the output buffer becomes full." So, deflate will not write more than avail_out to output buffer. If there is no enough space in output buffer for compressed data (it may be larger than input data) deflate just returns Z_OK. (if all data is compressed and written to output buffer deflate returns Z_STREAM_END). Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> --- v2: improve commit message block/qcow.c | 2 +- block/qcow2.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/block/qcow.c b/block/qcow.c index ac849bd..d8826f3 100644 --- a/block/qcow.c +++ b/block/qcow.c @@ -983,7 +983,7 @@ static int qcow_write_compressed(BlockDriverState *bs, int64_t sector_num, return ret; } - out_buf = g_malloc(s->cluster_size + (s->cluster_size / 1000) + 128); + out_buf = g_malloc(s->cluster_size); /* best compression, small window, no zlib header */ memset(&strm, 0, sizeof(strm)); diff --git a/block/qcow2.c b/block/qcow2.c index a5ea19b..b1c90ae 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -2612,7 +2612,7 @@ static int qcow2_write_compressed(BlockDriverState *bs, int64_t sector_num, return ret; } - out_buf = g_malloc(s->cluster_size + (s->cluster_size / 1000) + 128); + out_buf = g_malloc(s->cluster_size); /* best compression, small window, no zlib header */ memset(&strm, 0, sizeof(strm)); -- 1.8.3.1