[Qemu-devel] [PATCH] qcow2: do not allocate extra memory

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

There are no needs to allocate more than one cluster, as we set
avail_out for deflate to one cluster.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---

Hi all!

Please, can anybody say me what I'm missing?

I've looked through deflate documentation at
http://www.zlib.net/manual.html, and I didn't find anything about
allocating more memory for out buffer than specified in avail_out
field.. What is this magic formula?

========

All uses of out_buf in the function:

uint8_t *out_buf;
...
out_buf = g_malloc(s->cluster_size + (s->cluster_size / 1000) + 128);
...
strm.avail_out = s->cluster_size;
strm.next_out = out_buf;

ret = deflate(&strm, Z_FINISH);
...
out_len = strm.next_out - out_buf;
...
ret = bdrv_pwrite(bs->file, cluster_offset, out_buf, out_len);
...
g_free(out_buf);

 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