Am 03.06.2010 21:52, schrieb Miguel Di Ciurcio Filho:
> 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.fi...@gmail.com>
> ---
> block.c | 11 +++++++++++
> block.h | 1 +
> savevm.c | 58 ++++++++++++++++++++++++++++++++++++----------------------
> 3 files changed, 48 insertions(+), 22 deletions(-)
>
> diff --git a/block.c b/block.c
> index cd70730..ace3cdb 100644
> --- a/block.c
> +++ b/block.c
> @@ -1720,6 +1720,17 @@ void bdrv_debug_event(BlockDriverState *bs,
> BlkDebugEvent event)
> /**************************************************************/
> /* handling of snapshots */
>
> +int bdrv_can_snapshot(BlockDriverState *bs)
> +{
> + BlockDriver *drv = bs->drv;
> + if (!drv || !drv->bdrv_snapshot_create || bdrv_is_removable(bs) ||
> + bdrv_is_read_only(bs)) {
> + return 0;
> + }
> +
> + return 1;
> +}
> +
> int bdrv_snapshot_create(BlockDriverState *bs,
> QEMUSnapshotInfo *sn_info)
> {
> diff --git a/block.h b/block.h
> index 24efeb6..fbcd8af 100644
> --- a/block.h
> +++ b/block.h
> @@ -173,6 +173,7 @@ int bdrv_get_info(BlockDriverState *bs, BlockDriverInfo
> *bdi);
> const char *bdrv_get_encrypted_filename(BlockDriverState *bs);
> void bdrv_get_backing_filename(BlockDriverState *bs,
> char *filename, int filename_size);
> +int bdrv_can_snapshot(BlockDriverState *bs);
> int bdrv_snapshot_create(BlockDriverState *bs,
> QEMUSnapshotInfo *sn_info);
> int bdrv_snapshot_goto(BlockDriverState *bs,
> diff --git a/savevm.c b/savevm.c
> index dc20390..6549ca7 100644
> --- a/savevm.c
> +++ b/savevm.c
> @@ -1574,22 +1574,6 @@ out:
> return ret;
> }
>
> -/* device can contain snapshots */
> -static int bdrv_can_snapshot(BlockDriverState *bs)
> -{
> - return (bs &&
> - !bdrv_is_removable(bs) &&
> - !bdrv_is_read_only(bs));
> -}
> -
> -/* device must be snapshots in order to have a reliable snapshot */
> -static int bdrv_has_snapshot(BlockDriverState *bs)
> -{
> - return (bs &&
> - !bdrv_is_removable(bs) &&
> - !bdrv_is_read_only(bs));
> -}
> -
> static BlockDriverState *get_bs_snapshots(void)
> {
> BlockDriverState *bs;
> @@ -1599,8 +1583,9 @@ static BlockDriverState *get_bs_snapshots(void)
> return bs_snapshots;
> QTAILQ_FOREACH(dinfo, &drives, next) {
> bs = dinfo->bdrv;
> - if (bdrv_can_snapshot(bs))
> + if (bdrv_can_snapshot(bs)) {
> goto ok;
> + }
> }
> return NULL;
> ok:
> @@ -1674,12 +1659,26 @@ void do_savevm(Monitor *mon, const QDict *qdict)
> #endif
> const char *name = qdict_get_try_str(qdict, "name");
>
> + /* Verify if there is a device that doesn't support snapshots and is
> writable */
> + QTAILQ_FOREACH(dinfo, &drives, next) {
> + bs = dinfo->bdrv;
> +
> + if (bdrv_is_removable(bs) || bdrv_is_read_only(bs)) {
> + continue;
> + }
> +
> + if (!bdrv_can_snapshot(bs)) {
> + monitor_printf(mon, "Device '%s' is writable but does not
> support snapshots.\n",
> + bdrv_get_device_name(bs));
> + goto the_end;
cc1: warnings being treated as errors
savevm.c: In Funktion »do_savevm«:
savevm.c:1654: Fehler: »saved_vm_running« may be used uninitialized in
this function
return instead of goto the_end is probably the right thing to do here.
Kevin
