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block: Allow freezing BdrvChild links

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Our permission system is useful to define what operations are allowed
on a certain block node and includes things like BLK_PERM_WRITE or
BLK_PERM_RESIZE among others.

One of the permissions is BLK_PERM_GRAPH_MOD which allows "changing
the node that this BdrvChild points to". The exact meaning of this has
never been very clear, but it can be understood as "change any of the
links connected to the node". This can be used to prevent changing a
backing link, but it's too coarse.

This patch adds a new 'frozen' attribute to BdrvChild, which forbids
detaching the link from the node it points to, and new API to freeze
and unfreeze a backing chain.

After this change a few functions can fail, so they need additional
checks.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Alberto Garcia 2019-03-12 18:48:40 +02:00 • committed by Kevin Wolf
parent 9d6459d21a
commit 2cad1ebe70
3 changed files with 87 additions and 0 deletions
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5
include/block/block.h
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@ -353,6 +353,11 @@ int bdrv_drop_intermediate(BlockDriverState *top, BlockDriverState *base,
BlockDriverState *bdrv_find_overlay(BlockDriverState *active,
BlockDriverState *bs);
BlockDriverState *bdrv_find_base(BlockDriverState *bs);
bool bdrv_is_backing_chain_frozen(BlockDriverState *bs, BlockDriverState *base,
Error **errp);
int bdrv_freeze_backing_chain(BlockDriverState *bs, BlockDriverState *base,
Error **errp);
void bdrv_unfreeze_backing_chain(BlockDriverState *bs, BlockDriverState *base);
typedef struct BdrvCheckResult {