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author | Alberto Garcia <berto@igalia.com> | 2018-10-31 18:16:37 +0200 |
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committer | Kevin Wolf <kwolf@redhat.com> | 2018-11-22 19:37:31 +0100 |
commit | 0065c455f9f03ef5e830ede804a7404a8892fbc7 (patch) | |
tree | 6d763847564794aaf79f87e6db144fa15e55e2e8 /block.c | |
parent | a237dea330a2be9a2cbe95056b9a8d67627d95c6 (diff) | |
download | qemu-0065c455f9f03ef5e830ede804a7404a8892fbc7.zip qemu-0065c455f9f03ef5e830ede804a7404a8892fbc7.tar.gz qemu-0065c455f9f03ef5e830ede804a7404a8892fbc7.tar.bz2 |
block: Update BlockDriverState.inherits_from on bdrv_set_backing_hd()
When a BlockDriverState's child is opened (be it a backing file, the
protocol layer, or any other) inherits_from is set to point to the
parent node. Children opened separately and then attached to a parent
don't have this pointer set.
bdrv_reopen_queue_child() uses this to determine whether a node's
children must also be reopened inheriting the options from the parent
or not. If inherits_from points to the parent then the child is
reopened and its options can be changed, like in this example:
$ qemu-img create -f qcow2 hd0.qcow2 1M
$ qemu-img create -f qcow2 hd1.qcow2 1M
$ $QEMU -drive if=none,node-name=hd0,file=hd0.qcow2,\
backing.driver=qcow2,backing.file.filename=hd1.qcow2
(qemu) qemu-io hd0 "reopen -o backing.l2-cache-size=2M"
If the child does not inherit from the parent then it does not get
reopened and its options cannot be changed:
$ $QEMU -drive if=none,node-name=hd1,file=hd1.qcow2
-drive if=none,node-name=hd0,file=hd0.qcow2,backing=hd1
(qemu) qemu-io hd0 "reopen -o backing.l2-cache-size=2M"
Cannot change the option 'backing.l2-cache-size'
If a disk image has a chain of backing files then all of them are also
connected through their inherits_from pointers (i.e. it's possible to
walk the chain in reverse order from base to top).
However this is broken if the intermediate nodes are removed using
e.g. block-stream because the inherits_from pointer from the base node
becomes NULL:
$ qemu-img create -f qcow2 hd0.qcow2 1M
$ qemu-img create -f qcow2 -b hd0.qcow2 hd1.qcow2
$ qemu-img create -f qcow2 -b hd1.qcow2 hd2.qcow2
$ $QEMU -drive if=none,file=hd2.qcow2
(qemu) qemu-io none0 "reopen -o backing.l2-cache-size=2M"
(qemu) block_stream none0 0 hd0.qcow2
(qemu) qemu-io none0 "reopen -o backing.l2-cache-size=2M"
Cannot change the option 'backing.l2-cache-size'
This patch updates the inherits_from pointer if the intermediate nodes
of a backing chain are removed using bdrv_set_backing_hd(), and adds a
test case for this scenario.
Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'block.c')
-rw-r--r-- | block.c | 21 |
1 files changed, 21 insertions, 0 deletions
@@ -2260,6 +2260,18 @@ static void bdrv_parent_cb_change_media(BlockDriverState *bs, bool load) } } +/* Return true if you can reach parent going through child->inherits_from + * recursively. If parent or child are NULL, return false */ +static bool bdrv_inherits_from_recursive(BlockDriverState *child, + BlockDriverState *parent) +{ + while (child && child != parent) { + child = child->inherits_from; + } + + return child != NULL; +} + /* * Sets the backing file link of a BDS. A new reference is created; callers * which don't need their own reference any more must call bdrv_unref(). @@ -2267,6 +2279,9 @@ static void bdrv_parent_cb_change_media(BlockDriverState *bs, bool load) void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd, Error **errp) { + bool update_inherits_from = bdrv_chain_contains(bs, backing_hd) && + bdrv_inherits_from_recursive(backing_hd, bs); + if (backing_hd) { bdrv_ref(backing_hd); } @@ -2282,6 +2297,12 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd, bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_backing, errp); + /* If backing_hd was already part of bs's backing chain, and + * inherits_from pointed recursively to bs then let's update it to + * point directly to bs (else it will become NULL). */ + if (update_inherits_from) { + backing_hd->inherits_from = bs; + } if (!bs->backing) { bdrv_unref(backing_hd); } |