gluster: Return bdrv_has_zero_init = 0

GlusterFS volumes can be backed by block devices, in which case
bdrv_create() doesn't make sure that the image is zeroed out. It is
currently not possibly to detect whether a given image is backed by a
file or a block device, and incorrectly assuming that it is zeroed
corrupts images during qemu-img convert, so let's err on the side of
caution and always return 0.

Cc: qemu-stable@nongnu.org
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/gluster.c

@@ -574,6 +574,12 @@ static void qemu_gluster_close(BlockDriverState *bs)
     glfs_fini(s->glfs);
 }
 
+static int qemu_gluster_has_zero_init(BlockDriverState *bs)
+{
+    /* GlusterFS volume could be backed by a block device */
+    return 0;
+}
+
 static QEMUOptionParameter qemu_gluster_create_options[] = {
     {
         .name = BLOCK_OPT_SIZE,
@@ -595,6 +601,7 @@ static BlockDriver bdrv_gluster = {
     .bdrv_aio_readv               = qemu_gluster_aio_readv,
     .bdrv_aio_writev              = qemu_gluster_aio_writev,
     .bdrv_aio_flush               = qemu_gluster_aio_flush,
+    .bdrv_has_zero_init           = qemu_gluster_has_zero_init,
     .create_options               = qemu_gluster_create_options,
 };
 
@@ -610,6 +617,7 @@ static BlockDriver bdrv_gluster_tcp = {
     .bdrv_aio_readv               = qemu_gluster_aio_readv,
     .bdrv_aio_writev              = qemu_gluster_aio_writev,
     .bdrv_aio_flush               = qemu_gluster_aio_flush,
+    .bdrv_has_zero_init           = qemu_gluster_has_zero_init,
     .create_options               = qemu_gluster_create_options,
 };
 
@@ -625,6 +633,7 @@ static BlockDriver bdrv_gluster_unix = {
     .bdrv_aio_readv               = qemu_gluster_aio_readv,
     .bdrv_aio_writev              = qemu_gluster_aio_writev,
     .bdrv_aio_flush               = qemu_gluster_aio_flush,
+    .bdrv_has_zero_init           = qemu_gluster_has_zero_init,
     .create_options               = qemu_gluster_create_options,
 };
 
@@ -640,6 +649,7 @@ static BlockDriver bdrv_gluster_rdma = {
     .bdrv_aio_readv               = qemu_gluster_aio_readv,
     .bdrv_aio_writev              = qemu_gluster_aio_writev,
     .bdrv_aio_flush               = qemu_gluster_aio_flush,
+    .bdrv_has_zero_init           = qemu_gluster_has_zero_init,
     .create_options               = qemu_gluster_create_options,
 };