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block: Add bdrv_child_refresh_perms()

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If a block node uses bdrv_child_try_set_perm() to change the permission
it takes on its child, the result may be very short-lived.  If anything
makes the block layer recalculate the permissions internally, it will
invoke the node driver's .bdrv_child_perm() implementation.  The
permission/shared permissions masks that returns will then override the
values previously passed to bdrv_child_try_set_perm().

If drivers want a child edge to have specific values for the
permissions/shared permissions mask, it must return them in
.bdrv_child_perm().  Consequentially, there is no need for them to pass
the same values to bdrv_child_try_set_perm() then: It is better to have
a function that invokes .bdrv_child_perm() and calls
bdrv_child_try_set_perm() with the result.  This patch adds such a
function under the name of bdrv_child_refresh_perms().

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Max Reitz 2019-05-22 19:03:46 +02:00 committed by Kevin Wolf
parent 094e363944
commit c1087f1206
2 changed files with 27 additions and 0 deletions
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12
block.c
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@ -2083,6 +2083,18 @@ int bdrv_child_try_set_perm(BdrvChild *c, uint64_t perm, uint64_t shared,
return 0;
}
int bdrv_child_refresh_perms(BlockDriverState *bs, BdrvChild *c, Error **errp)
{
uint64_t parent_perms, parent_shared;
uint64_t perms, shared;
bdrv_get_cumulative_perm(bs, &parent_perms, &parent_shared);
bdrv_child_perm(bs, c->bs, c, c->role, NULL, parent_perms, parent_shared,
&perms, &shared);
return bdrv_child_try_set_perm(c, perms, shared, errp);
}
void bdrv_filter_default_perms(BlockDriverState *bs, BdrvChild *c,
const BdrvChildRole *role,
BlockReopenQueue *reopen_queue,

15
include/block/block_int.h
View File

@ -1165,9 +1165,24 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
void *opaque, Error **errp);
void bdrv_root_unref_child(BdrvChild *child);
/**
* Sets a BdrvChild's permissions. Avoid if the parent is a BDS; use
* bdrv_child_refresh_perms() instead and make the parent's
* .bdrv_child_perm() implementation return the correct values.
*/
int bdrv_child_try_set_perm(BdrvChild *c, uint64_t perm, uint64_t shared,
Error **errp);
/**
* Calls bs->drv->bdrv_child_perm() and updates the child's permission
* masks with the result.
* Drivers should invoke this function whenever an event occurs that
* makes their .bdrv_child_perm() implementation return different
* values than before, but which will not result in the block layer
* automatically refreshing the permissions.
*/
int bdrv_child_refresh_perms(BlockDriverState *bs, BdrvChild *c, Error **errp);
/* Default implementation for BlockDriver.bdrv_child_perm() that can be used by
* block filters: Forward CONSISTENT_READ, WRITE, WRITE_UNCHANGED and RESIZE to
* all children */