Am 28.05.2010 20:18, 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() and > bdrv_has_snapshot() actually do what they must do and enforces better tests to > avoid errors in the middle of do_savevm(). > > The functions were moved from savevm.c to block.c. It makes more sense to me. > > The bdrv_has_snapshot() is not beaultiful, but it does the job. I think having > this function avaible in the BlockDriver would be the best option. > > 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>
Markus, I think this implements mostly what we discussed the other day. Not sure if you already have a patch for doing this - if so, maybe could compare the patches and give it a review this way? I seem to remember that we came to the conclusion that bdrv_has_snapshot() isn't needed at all and should be dropped. Any user should be using bdrv_can_snapshot() instead as this is what they really want. > --- > block.c | 47 ++++++++++++++++++++++++++++++++++++++++++----- > block.h | 2 ++ > savevm.c | 48 +++++++++++++++++++++++++----------------------- > 3 files changed, 69 insertions(+), 28 deletions(-) > > diff --git a/block.c b/block.c > index cd70730..7eddc15 100644 > --- a/block.c > +++ b/block.c > @@ -1720,15 +1720,52 @@ void bdrv_debug_event(BlockDriverState *bs, > BlkDebugEvent event) > /**************************************************************/ > /* handling of snapshots */ > > -int bdrv_snapshot_create(BlockDriverState *bs, > - QEMUSnapshotInfo *sn_info) > +int bdrv_can_snapshot(BlockDriverState *bs) > { > BlockDriver *drv = bs->drv; > - if (!drv) > + if (!drv) { > + return -ENOMEDIUM; > + } > + > + if (!drv->bdrv_snapshot_create || bdrv_is_removable(bs) || > + bdrv_is_read_only(bs)) { > + return -ENOTSUP; > + } > + > + return 1; > +} Returning either 1 or -errno is a strange interface. I'm not sure which of 1/0 or 0/-errno is better in this case, but I'd suggest to take one of these. > +int bdrv_has_snapshot(BlockDriverState *bs) > +{ > + int ret; > + QEMUSnapshotInfo *sn_tab; > + BlockDriver *drv = bs->drv; > + if (!drv) { > return -ENOMEDIUM; > - if (!drv->bdrv_snapshot_create) > + } > + > + if (!drv->bdrv_snapshot_list) { > return -ENOTSUP; > - return drv->bdrv_snapshot_create(bs, sn_info); > + } > + > + ret = drv->bdrv_snapshot_list(bs, &sn_tab); > + > + if (sn_tab) { > + qemu_free(sn_tab); > + } > + > + return ret; > +} > + > +int bdrv_snapshot_create(BlockDriverState *bs, > + QEMUSnapshotInfo *sn_info) > +{ > + BlockDriver *drv = bs->drv; > + if (bdrv_can_snapshot(bs) > 0) { > + return drv->bdrv_snapshot_create(bs, sn_info); > + } > + > + return -1; > } > > int bdrv_snapshot_goto(BlockDriverState *bs, > diff --git a/block.h b/block.h > index 24efeb6..c536f1c 100644 > --- a/block.h > +++ b/block.h > @@ -173,6 +173,8 @@ 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_has_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..9bc232f 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; > @@ -1599,7 +1583,7 @@ 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) > 0) > goto ok; > } > return NULL; > @@ -1642,7 +1626,7 @@ static int del_existing_snapshots(Monitor *mon, const > char *name) > > QTAILQ_FOREACH(dinfo, &drives, next) { > bs = dinfo->bdrv; > - if (bdrv_can_snapshot(bs) && > + if ((bdrv_can_snapshot(bs) > 0) && > bdrv_snapshot_find(bs, snapshot, name) >= 0) > { > ret = bdrv_snapshot_delete(bs, name); > @@ -1674,12 +1658,30 @@ void do_savevm(Monitor *mon, const QDict *qdict) > #endif > const char *name = qdict_get_try_str(qdict, "name"); > > + /* Verify if there is have a device that doesn't support snapshots and > is writable*/ > + ret = 0; > + QTAILQ_FOREACH(dinfo, &drives, next) { > + bs = dinfo->bdrv; > + > + if (bdrv_is_removable(bs) || bdrv_is_read_only(bs)) { > + continue; > + } > + > + if ((ret = bdrv_can_snapshot(bs)) < 0) { This may overwrite the error of the previous loop iteration with a success return value. It's probably not what you want. Other than that it looks good to me. Kevin