crypto: perform permission checks under BQL

Move the permission API calls into driver-specific callbacks
that always run under BQL. In this case, bdrv_crypto_luks
needs to perform permission checks before and after
qcrypto_block_amend_options(). The problem is that the caller,
block_crypto_amend_options_generic_luks(), can also run in I/O
from .bdrv_co_amend(). This does not comply with Global State-I/O API split,
as permissions API must always run under BQL.

Firstly, introduce .bdrv_amend_pre_run() and .bdrv_amend_clean()
callbacks. These two callbacks are guaranteed to be invoked under
BQL, respectively before and after .bdrv_co_amend().
They take care of performing the permission checks
in the same way as they are currently done before and after
qcrypto_block_amend_options().
These callbacks are in preparation for next patch, where we
delete the original permission check. Right now they just add redundant
control.

Then, call .bdrv_amend_pre_run() before job_start in
qmp_x_blockdev_amend(), so that it will be run before the job coroutine
is created and stay in the main loop.
As a cleanup, use JobDriver's .clean() callback to call
.bdrv_amend_clean(), and run amend-specific cleanup callbacks under BQL.

After this patch, permission failures occur early in the blockdev-amend
job to update a LUKS volume's keys.  iotest 296 must now expect them in
x-blockdev-amend's QMP reply instead of waiting for the actual job to
fail later.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20220209105452.1694545-2-eesposit@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220304153729.711387-6-hreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/include/block/block_int.h b/include/block/block_int.h
index 27008cfb22..31bd788919 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -124,6 +124,20 @@ struct BlockDriver {
      * on those children.
      */
     bool is_format;
+
+    /*
+     * This function is invoked under BQL before .bdrv_co_amend()
+     * (which in contrast does not necessarily run under the BQL)
+     * to allow driver-specific initialization code that requires
+     * the BQL, like setting up specific permission flags.
+     */
+    int (*bdrv_amend_pre_run)(BlockDriverState *bs, Error **errp);
+    /*
+     * This function is invoked under BQL after .bdrv_co_amend()
+     * to allow cleaning up what was done in .bdrv_amend_pre_run().
+     */
+    void (*bdrv_amend_clean)(BlockDriverState *bs);
+
     /*
      * Return true if @to_replace can be replaced by a BDS with the
      * same data as @bs without it affecting @bs's behavior (that is,