gluster: Add image resize support

Implement .bdrv_truncate in GlusterFS block driver so that GlusterFS backend
can support image resizing.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Tested-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/gluster.c

@@ -493,6 +493,19 @@ out:
     return NULL;
 }
 
+static int qemu_gluster_truncate(BlockDriverState *bs, int64_t offset)
+{
+    int ret;
+    BDRVGlusterState *s = bs->opaque;
+
+    ret = glfs_ftruncate(s->fd, offset);
+    if (ret < 0) {
+        return -errno;
+    }
+
+    return 0;
+}
+
 static BlockDriverAIOCB *qemu_gluster_aio_readv(BlockDriverState *bs,
         int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
         BlockDriverCompletionFunc *cb, void *opaque)
@@ -631,6 +644,7 @@ static BlockDriver bdrv_gluster = {
     .bdrv_create                  = qemu_gluster_create,
     .bdrv_getlength               = qemu_gluster_getlength,
     .bdrv_get_allocated_file_size = qemu_gluster_allocated_file_size,
+    .bdrv_truncate                = qemu_gluster_truncate,
     .bdrv_aio_readv               = qemu_gluster_aio_readv,
     .bdrv_aio_writev              = qemu_gluster_aio_writev,
     .bdrv_aio_flush               = qemu_gluster_aio_flush,
@@ -650,6 +664,7 @@ static BlockDriver bdrv_gluster_tcp = {
     .bdrv_create                  = qemu_gluster_create,
     .bdrv_getlength               = qemu_gluster_getlength,
     .bdrv_get_allocated_file_size = qemu_gluster_allocated_file_size,
+    .bdrv_truncate                = qemu_gluster_truncate,
     .bdrv_aio_readv               = qemu_gluster_aio_readv,
     .bdrv_aio_writev              = qemu_gluster_aio_writev,
     .bdrv_aio_flush               = qemu_gluster_aio_flush,
@@ -669,6 +684,7 @@ static BlockDriver bdrv_gluster_unix = {
     .bdrv_create                  = qemu_gluster_create,
     .bdrv_getlength               = qemu_gluster_getlength,
     .bdrv_get_allocated_file_size = qemu_gluster_allocated_file_size,
+    .bdrv_truncate                = qemu_gluster_truncate,
     .bdrv_aio_readv               = qemu_gluster_aio_readv,
     .bdrv_aio_writev              = qemu_gluster_aio_writev,
     .bdrv_aio_flush               = qemu_gluster_aio_flush,
@@ -688,6 +704,7 @@ static BlockDriver bdrv_gluster_rdma = {
     .bdrv_create                  = qemu_gluster_create,
     .bdrv_getlength               = qemu_gluster_getlength,
     .bdrv_get_allocated_file_size = qemu_gluster_allocated_file_size,
+    .bdrv_truncate                = qemu_gluster_truncate,
     .bdrv_aio_readv               = qemu_gluster_aio_readv,
     .bdrv_aio_writev              = qemu_gluster_aio_writev,
     .bdrv_aio_flush               = qemu_gluster_aio_flush,