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authorMiguel Di Ciurcio Filho <miguel.filho@gmail.com>2010-06-08 10:40:55 -0300
committerKevin Wolf <kwolf@redhat.com>2010-06-15 09:41:58 +0200
commitfeeee5aca765606818e00f5a19d19f141f4ae365 (patch)
tree809c4ea64d59885195bf2dac10cfb891b08a103d /block.c
parente14e8ba5d059687bf276077da997c3ecfb5eab86 (diff)
savevm: Really verify if a drive supports snapshots
Both bdrv_can_snapshot() and bdrv_has_snapshot() does not work as advertized. First issue: Their names implies different porpouses, but they do the same thing and have exactly the same code. Maybe copied and pasted and forgotten? bdrv_has_snapshot() is called in various places for actually checking if there is snapshots or not. Second issue: the way bdrv_can_snapshot() verifies if a block driver supports or not snapshots does not catch all cases. E.g.: a raw image. So when do_savevm() is called, first thing it does is to set a global BlockDriverState to save the VM memory state calling get_bs_snapshots(). static BlockDriverState *get_bs_snapshots(void) { BlockDriverState *bs; DriveInfo *dinfo; if (bs_snapshots) return bs_snapshots; QTAILQ_FOREACH(dinfo, &drives, next) { bs = dinfo->bdrv; if (bdrv_can_snapshot(bs)) goto ok; } return NULL; ok: bs_snapshots = bs; return bs; } bdrv_can_snapshot() may return a BlockDriverState that does not support snapshots and do_savevm() goes on. Later on in do_savevm(), we find: QTAILQ_FOREACH(dinfo, &drives, next) { bs1 = dinfo->bdrv; if (bdrv_has_snapshot(bs1)) { /* Write VM state size only to the image that contains the state */ sn->vm_state_size = (bs == bs1 ? vm_state_size : 0); ret = bdrv_snapshot_create(bs1, sn); if (ret < 0) { monitor_printf(mon, "Error while creating snapshot on '%s'\n", bdrv_get_device_name(bs1)); } } } bdrv_has_snapshot(bs1) is not checking if the device does support or has snapshots as explained above. Only in bdrv_snapshot_create() the device is actually checked for snapshot support. So, in cases where the first device supports snapshots, and the second does not, the snapshot on the first will happen anyways. I believe this is not a good behavior. It should be an all or nothing process. This patch addresses these issues by making bdrv_can_snapshot() actually do what it must do and enforces better tests to avoid errors in the middle of do_savevm(). bdrv_has_snapshot() is removed and replaced by bdrv_can_snapshot() where appropriate. bdrv_can_snapshot() was moved from savevm.c to block.c. It makes more sense to me. The loadvm_state() function was updated too to enforce that when loading a VM at least all writable devices must support snapshots too. Signed-off-by: Miguel Di Ciurcio Filho <miguel.filho@gmail.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'block.c')
-rw-r--r--block.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/block.c b/block.c
index cacf11bd99..29a6f393df 100644
--- a/block.c
+++ b/block.c
@@ -1666,6 +1666,23 @@ void bdrv_debug_event(BlockDriverState *bs, BlkDebugEvent event)
/**************************************************************/
/* handling of snapshots */
+int bdrv_can_snapshot(BlockDriverState *bs)
+{
+ BlockDriver *drv = bs->drv;
+ if (!drv || bdrv_is_removable(bs) || bdrv_is_read_only(bs)) {
+ return 0;
+ }
+
+ if (!drv->bdrv_snapshot_create) {
+ if (bs->file != NULL) {
+ return bdrv_can_snapshot(bs->file);
+ }
+ return 0;
+ }
+
+ return 1;
+}
+
int bdrv_snapshot_create(BlockDriverState *bs,
QEMUSnapshotInfo *sn_info)
{