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> --- 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; +} + +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) { + monitor_printf(mon, "Device '%s' is writable but does not support snapshots.\n", + bdrv_get_device_name(bs)); + } + } + + if (ret < 0) { + goto the_end; + } + bs = get_bs_snapshots(); if (!bs) { monitor_printf(mon, "No block device can accept snapshots\n"); return; } - /* ??? Should this occur after vm_stop? */ qemu_aio_flush(); @@ -1732,7 +1734,7 @@ void do_savevm(Monitor *mon, const QDict *qdict) QTAILQ_FOREACH(dinfo, &drives, next) { bs1 = dinfo->bdrv; - if (bdrv_has_snapshot(bs1)) { + if (bdrv_can_snapshot(bs1) > 0) { /* 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); @@ -1767,7 +1769,7 @@ int load_vmstate(const char *name) QTAILQ_FOREACH(dinfo, &drives, next) { bs1 = dinfo->bdrv; - if (bdrv_has_snapshot(bs1)) { + if (bdrv_has_snapshot(bs1) > 0) { ret = bdrv_snapshot_goto(bs1, name); if (ret < 0) { switch(ret) { @@ -1829,7 +1831,7 @@ void do_delvm(Monitor *mon, const QDict *qdict) QTAILQ_FOREACH(dinfo, &drives, next) { bs1 = dinfo->bdrv; - if (bdrv_has_snapshot(bs1)) { + if (bdrv_has_snapshot(bs1) > 0) { ret = bdrv_snapshot_delete(bs1, name); if (ret < 0) { if (ret == -ENOTSUP) @@ -1860,7 +1862,7 @@ void do_info_snapshots(Monitor *mon) monitor_printf(mon, "Snapshot devices:"); QTAILQ_FOREACH(dinfo, &drives, next) { bs1 = dinfo->bdrv; - if (bdrv_has_snapshot(bs1)) { + if (bdrv_can_snapshot(bs1) > 0) { if (bs == bs1) monitor_printf(mon, " %s", bdrv_get_device_name(bs1)); } -- 1.7.1