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block: Re-evaluate backing file handling in reopen 

Reopening a node's backing child needs a bit of special handling because
the "backing" child has different defaults than all other children
(among other things).  Adding filter support here is a bit more
difficult than just using the child access functions.  In fact, we often
have to directly use bs->backing because these functions are about the
"backing" child (which may or may not be the COW backing file).

Signed-off-by: Max Reitz <mreitz@redhat.com>
This commit is contained in:
Max Reitz 2019-06-12 17:24:39 +02:00 committed by Kevin Wolf
parent 23b93525a2
commit 1d42f48c3a
1 changed files with 40 additions and 9 deletions
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49
block.c
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@ -4004,7 +4004,7 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
Error **errp)
{
BlockDriverState *bs = reopen_state->bs;
BlockDriverState *overlay_bs, *new_backing_bs;
BlockDriverState *overlay_bs, *below_bs, *new_backing_bs;
QObject *value;
const char *str;
@ -4043,26 +4043,57 @@ static int bdrv_reopen_parse_backing(BDRVReopenState *reopen_state,
}
}
/*
* Ensure that @bs can really handle backing files, because we are
* about to give it one (or swap the existing one)
*/
if (bs->drv->is_filter) {
/* Filters always have a file or a backing child */
if (!bs->backing) {
error_setg(errp, "'%s' is a %s filter node that does not support a "
"backing child", bs->node_name, bs->drv->format_name);
return -EINVAL;
}
} else if (!bs->drv->supports_backing) {
error_setg(errp, "Driver '%s' of node '%s' does not support backing "
"files", bs->drv->format_name, bs->node_name);
return -EINVAL;
}
/*
* Find the "actual" backing file by skipping all links that point
* to an implicit node, if any (e.g. a commit filter node).
* We cannot use any of the bdrv_skip_*() functions here because
* those return the first explicit node, while we are looking for
* its overlay here.
*/
overlay_bs = bs;
while (backing_bs(overlay_bs) && backing_bs(overlay_bs)->implicit) {
overlay_bs = backing_bs(overlay_bs);
for (below_bs = bdrv_filter_or_cow_bs(overlay_bs);
below_bs && below_bs->implicit;
below_bs = bdrv_filter_or_cow_bs(overlay_bs))
{
overlay_bs = below_bs;
}
/* If we want to replace the backing file we need some extra checks */
if (new_backing_bs != backing_bs(overlay_bs)) {
if (new_backing_bs != bdrv_filter_or_cow_bs(overlay_bs)) {
/* Check for implicit nodes between bs and its backing file */
if (bs != overlay_bs) {
error_setg(errp, "Cannot change backing link if '%s' has "
"an implicit backing file", bs->node_name);
return -EPERM;
}
/* Check if the backing link that we want to replace is frozen */
if (bdrv_is_backing_chain_frozen(overlay_bs, backing_bs(overlay_bs),
errp)) {
/*
* Check if the backing link that we want to replace is frozen.
* Note that
* bdrv_filter_or_cow_child(overlay_bs) == overlay_bs->backing,
* because we know that overlay_bs == bs, and that @bs
* either is a filter that uses ->backing or a COW format BDS
* with bs->drv->supports_backing == true.
*/
if (bdrv_is_backing_chain_frozen(overlay_bs,
child_bs(overlay_bs->backing), errp))
{
return -EPERM;
}
reopen_state->replace_backing_bs = true;
@ -4211,7 +4242,7 @@ int bdrv_reopen_prepare(BDRVReopenState *reopen_state, BlockReopenQueue *queue,
* its metadata. Otherwise the 'backing' option can be omitted.
*/
if (drv->supports_backing && reopen_state->backing_missing &&
(backing_bs(reopen_state->bs) || reopen_state->bs->backing_file[0])) {
(reopen_state->bs->backing || reopen_state->bs->backing_file[0])) {
error_setg(errp, "backing is missing for '%s'",
reopen_state->bs->node_name);
ret = -EINVAL;
@ -4352,7 +4383,7 @@ void bdrv_reopen_commit(BDRVReopenState *reopen_state)
* from bdrv_set_backing_hd()) has the new values.
*/
if (reopen_state->replace_backing_bs) {
BlockDriverState *old_backing_bs = backing_bs(bs);
BlockDriverState *old_backing_bs = child_bs(bs->backing);
assert(!old_backing_bs || !old_backing_bs->implicit);
/* Abort the permission update on the backing bs we're detaching */
if (old_backing_bs) {