block: Ignore loosening perm restrictions failures
We generally assume that loosening permission restrictions can never fail. We have seen in the past that this assumption is wrong. This has led to crashes because we generally pass &error_abort when loosening permissions. However, a failure in such a case should actually be handled in quite the opposite way: It is very much not fatal, so qemu may report it, but still consider the operation successful. The only realistic problem is that qemu may then retain permissions and thus locks on images it actually does not require. But again, that is not fatal. To implement this behavior, we make all functions that change permissions and that pass &error_abort to the initiating function (bdrv_check_perm() or bdrv_child_check_perm()) evaluate the @loosen_restrictions value introduced in the previous patch. If it is true and an error did occur, we abort the permission update, discard the error, and instead report success to the caller. bdrv_child_try_set_perm() itself does not pass &error_abort, but it is the only public function to change permissions. As such, callers may pass &error_abort to it, expecting dropping permission restrictions to never fail. Signed-off-by: NMax Reitz <mreitz@redhat.com> Signed-off-by: NKevin Wolf <kwolf@redhat.com>
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