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blockdev: Allow external snapshots everywhere
There is no good reason why we would allow external snapshots only on the first non-filter node in a chain. Parent BDSs should not care whether their child is replaced by a snapshot. (If they do care, they should announce that via freezing the chain, which is checked in bdrv_append() through bdrv_set_backing_hd().) Before we had bdrv_is_first_non_filter() here (since212a5a8f09
), there was a special function bdrv_check_ext_snapshot() that allowed snapshots by default, but block drivers could override this. Only blkverify did so, however. It is not clear to me why blkverify would do so; maybe just so that the testee block driver would not be replaced. The introducing commitf6186f49e2
does not explain why. Maybe because08b24cfe37
would have been the correct solution? (Which adds a .supports_backing check.) Signed-off-by: Max Reitz <mreitz@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Message-Id: <20200218103454.296704-2-mreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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@ -1592,11 +1592,6 @@ static void external_snapshot_prepare(BlkActionState *common,
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}
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}
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if (!bdrv_is_first_non_filter(state->old_bs)) {
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error_setg(errp, QERR_FEATURE_DISABLED, "snapshot");
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goto out;
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}
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if (action->type == TRANSACTION_ACTION_KIND_BLOCKDEV_SNAPSHOT_SYNC) {
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BlockdevSnapshotSync *s = action->u.blockdev_snapshot_sync.data;
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const char *format = s->has_format ? s->format : "qcow2";
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