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block: fix external snapshot abort permission error

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In external_snapshot_abort(), we try to undo what was done in
external_snapshot_prepare() calling bdrv_replace_node() to swap the
nodes back.  However, we receive a permissions error as writers are
blocked on the old node, which is now the new node backing file.

An easy fix (initially suggested by Kevin Wolf) is to call
bdrv_set_backing_hd() on the new node, to set the backing node to NULL.

Signed-off-by: Jeff Cody <jcody@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Jeff Cody 2017-06-07 09:55:22 -04:00 committed by Kevin Wolf
parent 272545cf21
commit 719fc28c80
1 changed files with 4 additions and 0 deletions
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4
blockdev.c
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@ -1803,7 +1803,11 @@ static void external_snapshot_abort(BlkActionState *common)
DO_UPCAST(ExternalSnapshotState, common, common);
if (state->new_bs) {
if (state->overlay_appended) {
bdrv_ref(state->old_bs); /* we can't let bdrv_set_backind_hd()
close state->old_bs; we need it */
bdrv_set_backing_hd(state->new_bs, NULL, &error_abort);
bdrv_replace_node(state->new_bs, state->old_bs, &error_abort);
bdrv_unref(state->old_bs); /* bdrv_replace_node() ref'ed old_bs */
}
}
}