[PATCH 1/5] crypto: perform permission checks under BQL

[Emanuele Giuseppe Esposito <eesposit@redhat.com>]

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.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
 block/amend.c             | 24 ++++++++++++++++++++++++
 block/crypto.c            | 27 +++++++++++++++++++++++++++
 include/block/block_int.h | 14 ++++++++++++++
 3 files changed, 65 insertions(+)

diff --git a/block/amend.c b/block/amend.c
index 392df9ef83..329bca53dc 100644
--- a/block/amend.c
+++ b/block/amend.c
@@ -53,10 +53,29 @@ static int coroutine_fn blockdev_amend_run(Job *job, Error **errp)
     return ret;
 }
 
+static int blockdev_amend_pre_run(BlockdevAmendJob *s, Error **errp)
+{
+    if (s->bs->drv->bdrv_amend_pre_run) {
+        return s->bs->drv->bdrv_amend_pre_run(s->bs, errp);
+    }
+
+    return 0;
+}
+
+static void blockdev_amend_clean(Job *job)
+{
+    BlockdevAmendJob *s = container_of(job, BlockdevAmendJob, common);
+
+    if (s->bs->drv->bdrv_amend_clean) {
+        s->bs->drv->bdrv_amend_clean(s->bs);
+    }
+}
+
 static const JobDriver blockdev_amend_job_driver = {
     .instance_size = sizeof(BlockdevAmendJob),
     .job_type      = JOB_TYPE_AMEND,
     .run           = blockdev_amend_run,
+    .clean         = blockdev_amend_clean,
 };
 
 void qmp_x_blockdev_amend(const char *job_id,
@@ -113,5 +132,10 @@ void qmp_x_blockdev_amend(const char *job_id,
     s->bs = bs,
     s->opts = QAPI_CLONE(BlockdevAmendOptions, options),
     s->force = has_force ? force : false;
+
+    if (blockdev_amend_pre_run(s, errp)) {
+        return;
+    }
+
     job_start(&s->common);
 }
diff --git a/block/crypto.c b/block/crypto.c
index c8ba4681e2..59f768ea8d 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -777,6 +777,31 @@ block_crypto_get_specific_info_luks(BlockDriverState *bs, Error **errp)
     return spec_info;
 }
 
+static int
+block_crypto_amend_prepare(BlockDriverState *bs, Error **errp)
+{
+    BlockCrypto *crypto = bs->opaque;
+
+    /* apply for exclusive read/write permissions to the underlying file*/
+    crypto->updating_keys = true;
+    return bdrv_child_refresh_perms(bs, bs->file, errp);
+}
+
+static void
+block_crypto_amend_cleanup(BlockDriverState *bs)
+{
+    BlockCrypto *crypto = bs->opaque;
+    Error *errp = NULL;
+
+    /* release exclusive read/write permissions to the underlying file*/
+    crypto->updating_keys = false;
+    bdrv_child_refresh_perms(bs, bs->file, &errp);
+
+    if (errp) {
+        error_report_err(errp);
+    }
+}
+
 static int
 block_crypto_amend_options_generic_luks(BlockDriverState *bs,
                                         QCryptoBlockAmendOptions *amend_options,
@@ -931,6 +956,8 @@ static BlockDriver bdrv_crypto_luks = {
     .bdrv_get_specific_info = block_crypto_get_specific_info_luks,
     .bdrv_amend_options = block_crypto_amend_options_luks,
     .bdrv_co_amend      = block_crypto_co_amend_luks,
+    .bdrv_amend_pre_run = block_crypto_amend_prepare,
+    .bdrv_amend_clean   = block_crypto_amend_cleanup,
 
     .is_format          = true,
 
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,
-- 
2.31.1