From: Stefan Hajnoczi <stefanha@redhat.com>
Date: Mon, 15 Apr 2013 15:17:31 +0000 (+0200)
Subject: qcow2: allow sub-cluster compressed write to last cluster
X-Git-Tag: v1.5.0-rc0~196^2~19
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=f4d38bef7cc79018e2aa789b0e4c23c3a8cdfca5;p=users%2Fdwmw2%2Fqemu.git

qcow2: allow sub-cluster compressed write to last cluster

Compression in qcow2 requires image length to be a multiple of the
cluster size.  Lift this requirement by zero-padding the final cluster
when necessary.  The virtual disk size is still not cluster-aligned, so
the guest cannot access the zero sectors.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---

diff --git a/block/qcow2.c b/block/qcow2.c
index e8934de185..2e346d8c42 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1537,8 +1537,21 @@ static int qcow2_write_compressed(BlockDriverState *bs, int64_t sector_num,
         return 0;
     }
 
-    if (nb_sectors != s->cluster_sectors)
-        return -EINVAL;
+    if (nb_sectors != s->cluster_sectors) {
+        ret = -EINVAL;
+
+        /* Zero-pad last write if image size is not cluster aligned */
+        if (sector_num + nb_sectors == bs->total_sectors &&
+            nb_sectors < s->cluster_sectors) {
+            uint8_t *pad_buf = qemu_blockalign(bs, s->cluster_size);
+            memset(pad_buf, 0, s->cluster_size);
+            memcpy(pad_buf, buf, nb_sectors * BDRV_SECTOR_SIZE);
+            ret = qcow2_write_compressed(bs, sector_num,
+                                         pad_buf, s->cluster_sectors);
+            qemu_vfree(pad_buf);
+        }
+        return ret;
+    }
 
     out_buf = g_malloc(s->cluster_size + (s->cluster_size / 1000) + 128);