diff mbox

[v5,22/38] block: Prepare for NULL BDS

Message ID 1442589793-7105-23-git-send-email-mreitz@redhat.com
State New
Headers show

Commit Message

Max Reitz Sept. 18, 2015, 3:22 p.m. UTC 
blk_bs() will not necessarily return a non-NULL value any more (unless
blk_is_available() is true or it can be assumed to otherwise, e.g.
because it is called immediately after a successful blk_new_with_bs() or
blk_new_open()).

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block.c             |   5 ++
 block/qapi.c        |   4 +-
 blockdev.c          | 201 ++++++++++++++++++++++++++++++++++------------------
 hw/block/xen_disk.c |   4 +-
 migration/block.c   |   5 ++
 monitor.c           |   4 ++
 6 files changed, 153 insertions(+), 70 deletions(-)

Comments

Eric Blake Sept. 18, 2015, 7:42 p.m. UTC | #1 
On 09/18/2015 09:22 AM, Max Reitz wrote:
> blk_bs() will not necessarily return a non-NULL value any more (unless
> blk_is_available() is true or it can be assumed to otherwise, e.g.
> because it is called immediately after a successful blk_new_with_bs() or
> blk_new_open()).
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>
> ---
>  block.c             |   5 ++
>  block/qapi.c        |   4 +-
>  blockdev.c          | 201 ++++++++++++++++++++++++++++++++++------------------
>  hw/block/xen_disk.c |   4 +-
>  migration/block.c   |   5 ++
>  monitor.c           |   4 ++
>  6 files changed, 153 insertions(+), 70 deletions(-)
> 

Reviewed-by: Eric Blake <eblake@redhat.com>
Kevin Wolf Oct. 7, 2015, 10:43 a.m. UTC | #2 
Am 18.09.2015 um 17:22 hat Max Reitz geschrieben:
> blk_bs() will not necessarily return a non-NULL value any more (unless
> blk_is_available() is true or it can be assumed to otherwise, e.g.
> because it is called immediately after a successful blk_new_with_bs() or
> blk_new_open()).
> 
> Signed-off-by: Max Reitz <mreitz@redhat.com>

> @@ -1922,8 +1939,9 @@ void qmp_change_blockdev(const char *device, const char *filename,
>          return;
>      }
>      bs = blk_bs(blk);
> +    new_bs = !bs;
>  
> -    aio_context = bdrv_get_aio_context(bs);
> +    aio_context = blk_get_aio_context(blk);
>      aio_context_acquire(aio_context);
>  
>      eject_device(blk, 0, &err);
> @@ -1932,10 +1950,18 @@ void qmp_change_blockdev(const char *device, const char *filename,
>          goto out;
>      }
>  
> -    bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
> -    bdrv_flags |= bdrv_is_snapshot(bs) ? BDRV_O_SNAPSHOT : 0;
> +    bdrv_flags = blk_is_read_only(blk) ? 0 : BDRV_O_RDWR;
> +    bdrv_flags |= blk_get_root_state(blk)->open_flags & ~BDRV_O_RDWR;
>  
> -    qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, format, NULL, errp);
> +    qmp_bdrv_open_encrypted(&bs, filename, bdrv_flags, format, NULL, &err);
> +    if (err) {
> +        error_propagate(errp, err);
> +    } else if (new_bs) {
> +        blk_insert_bs(blk, bs);
> +        /* Has been sent automatically by bdrv_open() if blk_bs(blk) was not
> +         * NULL */
> +        blk_dev_change_media_cb(blk, true);
> +    }

Was this change supposed to be in this patch? It looks like it's doing a
bit more than just fixing blk_bs() == NULL cases.

Kevin
Max Reitz Oct. 7, 2015, 3:08 p.m. UTC | #3 
On 07.10.2015 12:43, Kevin Wolf wrote:
> Am 18.09.2015 um 17:22 hat Max Reitz geschrieben:
>> blk_bs() will not necessarily return a non-NULL value any more (unless
>> blk_is_available() is true or it can be assumed to otherwise, e.g.
>> because it is called immediately after a successful blk_new_with_bs() or
>> blk_new_open()).
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
> 
>> @@ -1922,8 +1939,9 @@ void qmp_change_blockdev(const char *device, const char *filename,
>>          return;
>>      }
>>      bs = blk_bs(blk);
>> +    new_bs = !bs;
>>  
>> -    aio_context = bdrv_get_aio_context(bs);
>> +    aio_context = blk_get_aio_context(blk);
>>      aio_context_acquire(aio_context);
>>  
>>      eject_device(blk, 0, &err);
>> @@ -1932,10 +1950,18 @@ void qmp_change_blockdev(const char *device, const char *filename,
>>          goto out;
>>      }
>>  
>> -    bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
>> -    bdrv_flags |= bdrv_is_snapshot(bs) ? BDRV_O_SNAPSHOT : 0;
>> +    bdrv_flags = blk_is_read_only(blk) ? 0 : BDRV_O_RDWR;
>> +    bdrv_flags |= blk_get_root_state(blk)->open_flags & ~BDRV_O_RDWR;
>>  
>> -    qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, format, NULL, errp);
>> +    qmp_bdrv_open_encrypted(&bs, filename, bdrv_flags, format, NULL, &err);
>> +    if (err) {
>> +        error_propagate(errp, err);
>> +    } else if (new_bs) {
>> +        blk_insert_bs(blk, bs);
>> +        /* Has been sent automatically by bdrv_open() if blk_bs(blk) was not
>> +         * NULL */
>> +        blk_dev_change_media_cb(blk, true);
>> +    }
> 
> Was this change supposed to be in this patch? It looks like it's doing a
> bit more than just fixing blk_bs() == NULL cases.

Yes, it's supposed to be here. Before this patch, qmp_change_blockdev()
took the BDS from the specified BB, closed it (eject_device()) and
"re-opened" it (bdrv_open() in qmp_bdrv_open_encrypted()), and we're done.

Now, the BB does not have to have a BDS anymore. In this case
(new_bs == true) qmp_bdrv_open_encrypted() will now create a new BDS
(which is why now it needs to take a BDS ** instead of a plain BDS *)
and we have to then attach it to the BB.

The comment above blk_dev_change_media_cb() then explains why we need
that, too.

Later ("Implement change with basic operations") I'll drop it altogether
anyway, and then, since the "eject" part of "change" will then detach
the BDS from the BB, we'll always have the "need to attach a new BDS to
the BB" case.

Max
diff mbox

Patch

diff --git a/block.c b/block.c
index 67a39fb..7776871 100644
--- a/block.c
+++ b/block.c
@@ -2787,6 +2787,11 @@  BlockDriverState *bdrv_lookup_bs(const char *device,
         blk = blk_by_name(device);
 
         if (blk) {
+            if (!blk_bs(blk)) {
+                error_setg(errp, "Device '%s' has no medium", device);
+                return NULL;
+            }
+
             return blk_bs(blk);
         }
     }
diff --git a/block/qapi.c b/block/qapi.c
index f295692..e936ba7 100644
--- a/block/qapi.c
+++ b/block/qapi.c
@@ -306,12 +306,12 @@  static void bdrv_query_info(BlockBackend *blk, BlockInfo **p_info,
         info->io_status = blk_iostatus(blk);
     }
 
-    if (!QLIST_EMPTY(&bs->dirty_bitmaps)) {
+    if (bs && !QLIST_EMPTY(&bs->dirty_bitmaps)) {
         info->has_dirty_bitmaps = true;
         info->dirty_bitmaps = bdrv_query_dirty_bitmaps(bs);
     }
 
-    if (bs->drv) {
+    if (bs && bs->drv) {
         info->has_inserted = true;
         info->inserted = bdrv_block_device_info(bs, errp);
         if (info->inserted == NULL) {
diff --git a/blockdev.c b/blockdev.c
index 01d422e..6168b09 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -124,14 +124,16 @@  void blockdev_mark_auto_del(BlockBackend *blk)
         return;
     }
 
-    aio_context = bdrv_get_aio_context(bs);
-    aio_context_acquire(aio_context);
+    if (bs) {
+        aio_context = bdrv_get_aio_context(bs);
+        aio_context_acquire(aio_context);
 
-    if (bs->job) {
-        block_job_cancel(bs->job);
-    }
+        if (bs->job) {
+            block_job_cancel(bs->job);
+        }
 
-    aio_context_release(aio_context);
+        aio_context_release(aio_context);
+    }
 
     dinfo->auto_del = 1;
 }
@@ -229,8 +231,8 @@  bool drive_check_orphaned(void)
             dinfo->type != IF_NONE) {
             fprintf(stderr, "Warning: Orphaned drive without device: "
                     "id=%s,file=%s,if=%s,bus=%d,unit=%d\n",
-                    blk_name(blk), blk_bs(blk)->filename, if_name[dinfo->type],
-                    dinfo->bus, dinfo->unit);
+                    blk_name(blk), blk_bs(blk) ? blk_bs(blk)->filename : "",
+                    if_name[dinfo->type], dinfo->bus, dinfo->unit);
             rs = true;
         }
     }
@@ -1040,6 +1042,10 @@  void hmp_commit(Monitor *mon, const QDict *qdict)
             monitor_printf(mon, "Device '%s' not found\n", device);
             return;
         }
+        if (!blk_is_available(blk)) {
+            monitor_printf(mon, "Device '%s' has no medium\n", device);
+            return;
+        }
         ret = bdrv_commit(blk_bs(blk));
     }
     if (ret < 0) {
@@ -1119,7 +1125,9 @@  SnapshotInfo *qmp_blockdev_snapshot_delete_internal_sync(const char *device,
                   "Device '%s' not found", device);
         return NULL;
     }
-    bs = blk_bs(blk);
+
+    aio_context = blk_get_aio_context(blk);
+    aio_context_acquire(aio_context);
 
     if (!has_id) {
         id = NULL;
@@ -1131,11 +1139,14 @@  SnapshotInfo *qmp_blockdev_snapshot_delete_internal_sync(const char *device,
 
     if (!id && !name) {
         error_setg(errp, "Name or id must be provided");
-        return NULL;
+        goto out_aio_context;
     }
 
-    aio_context = bdrv_get_aio_context(bs);
-    aio_context_acquire(aio_context);
+    if (!blk_is_available(blk)) {
+        error_setg(errp, "Device '%s' has no medium", device);
+        goto out_aio_context;
+    }
+    bs = blk_bs(blk);
 
     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_INTERNAL_SNAPSHOT_DELETE, errp)) {
         goto out_aio_context;
@@ -1309,16 +1320,16 @@  static void internal_snapshot_prepare(BlkTransactionState *common,
                   "Device '%s' not found", device);
         return;
     }
-    bs = blk_bs(blk);
 
     /* AioContext is released in .clean() */
-    state->aio_context = bdrv_get_aio_context(bs);
+    state->aio_context = blk_get_aio_context(blk);
     aio_context_acquire(state->aio_context);
 
-    if (!bdrv_is_inserted(bs)) {
+    if (!blk_is_available(blk)) {
         error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
         return;
     }
+    bs = blk_bs(blk);
 
     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_INTERNAL_SNAPSHOT, errp)) {
         return;
@@ -1570,7 +1581,6 @@  typedef struct DriveBackupState {
 static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
 {
     DriveBackupState *state = DO_UPCAST(DriveBackupState, common, common);
-    BlockDriverState *bs;
     BlockBackend *blk;
     DriveBackup *backup;
     Error *local_err = NULL;
@@ -1584,12 +1594,16 @@  static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
                   "Device '%s' not found", backup->device);
         return;
     }
-    bs = blk_bs(blk);
 
     /* AioContext is released in .clean() */
-    state->aio_context = bdrv_get_aio_context(bs);
+    state->aio_context = blk_get_aio_context(blk);
     aio_context_acquire(state->aio_context);
 
+    if (!blk_is_available(blk)) {
+        error_setg(errp, "Device '%s' has no medium", backup->device);
+        return;
+    }
+
     qmp_drive_backup(backup->device, backup->target,
                      backup->has_format, backup->format,
                      backup->sync,
@@ -1604,7 +1618,7 @@  static void drive_backup_prepare(BlkTransactionState *common, Error **errp)
         return;
     }
 
-    state->bs = bs;
+    state->bs = blk_bs(blk);
     state->job = state->bs->job;
 }
 
@@ -1639,8 +1653,7 @@  static void blockdev_backup_prepare(BlkTransactionState *common, Error **errp)
 {
     BlockdevBackupState *state = DO_UPCAST(BlockdevBackupState, common, common);
     BlockdevBackup *backup;
-    BlockDriverState *bs, *target;
-    BlockBackend *blk;
+    BlockBackend *blk, *target;
     Error *local_err = NULL;
 
     assert(common->action->kind == TRANSACTION_ACTION_KIND_BLOCKDEV_BACKUP);
@@ -1651,18 +1664,16 @@  static void blockdev_backup_prepare(BlkTransactionState *common, Error **errp)
         error_setg(errp, "Device '%s' not found", backup->device);
         return;
     }
-    bs = blk_bs(blk);
 
-    blk = blk_by_name(backup->target);
-    if (!blk) {
+    target = blk_by_name(backup->target);
+    if (!target) {
         error_setg(errp, "Device '%s' not found", backup->target);
         return;
     }
-    target = blk_bs(blk);
 
     /* AioContext is released in .clean() */
-    state->aio_context = bdrv_get_aio_context(bs);
-    if (state->aio_context != bdrv_get_aio_context(target)) {
+    state->aio_context = blk_get_aio_context(blk);
+    if (state->aio_context != blk_get_aio_context(target)) {
         state->aio_context = NULL;
         error_setg(errp, "Backup between two IO threads is not implemented");
         return;
@@ -1680,7 +1691,7 @@  static void blockdev_backup_prepare(BlkTransactionState *common, Error **errp)
         return;
     }
 
-    state->bs = bs;
+    state->bs = blk_bs(blk);
     state->job = state->bs->job;
 }
 
@@ -1818,10 +1829,10 @@  static void eject_device(BlockBackend *blk, int force, Error **errp)
     BlockDriverState *bs = blk_bs(blk);
     AioContext *aio_context;
 
-    aio_context = bdrv_get_aio_context(bs);
+    aio_context = blk_get_aio_context(blk);
     aio_context_acquire(aio_context);
 
-    if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_EJECT, errp)) {
+    if (bs && bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_EJECT, errp)) {
         goto out;
     }
     if (!blk_dev_has_removable_media(blk)) {
@@ -1839,7 +1850,9 @@  static void eject_device(BlockBackend *blk, int force, Error **errp)
         }
     }
 
-    bdrv_close(bs);
+    if (bs) {
+        bdrv_close(bs);
+    }
 
 out:
     aio_context_release(aio_context);
@@ -1884,10 +1897,12 @@  void qmp_block_passwd(bool has_device, const char *device,
 }
 
 /* Assumes AioContext is held */
-static void qmp_bdrv_open_encrypted(BlockDriverState *bs, const char *filename,
+static void qmp_bdrv_open_encrypted(BlockDriverState **pbs,
+                                    const char *filename,
                                     int bdrv_flags, const char *format,
                                     const char *password, Error **errp)
 {
+    BlockDriverState *bs;
     Error *local_err = NULL;
     QDict *options = NULL;
     int ret;
@@ -1897,11 +1912,12 @@  static void qmp_bdrv_open_encrypted(BlockDriverState *bs, const char *filename,
         qdict_put(options, "driver", qstring_from_str(format));
     }
 
-    ret = bdrv_open(&bs, filename, NULL, options, bdrv_flags, &local_err);
+    ret = bdrv_open(pbs, filename, NULL, options, bdrv_flags, &local_err);
     if (ret < 0) {
         error_propagate(errp, local_err);
         return;
     }
+    bs = *pbs;
 
     bdrv_add_key(bs, password, errp);
 }
@@ -1913,6 +1929,7 @@  void qmp_change_blockdev(const char *device, const char *filename,
     BlockDriverState *bs;
     AioContext *aio_context;
     int bdrv_flags;
+    bool new_bs;
     Error *err = NULL;
 
     blk = blk_by_name(device);
@@ -1922,8 +1939,9 @@  void qmp_change_blockdev(const char *device, const char *filename,
         return;
     }
     bs = blk_bs(blk);
+    new_bs = !bs;
 
-    aio_context = bdrv_get_aio_context(bs);
+    aio_context = blk_get_aio_context(blk);
     aio_context_acquire(aio_context);
 
     eject_device(blk, 0, &err);
@@ -1932,10 +1950,18 @@  void qmp_change_blockdev(const char *device, const char *filename,
         goto out;
     }
 
-    bdrv_flags = bdrv_is_read_only(bs) ? 0 : BDRV_O_RDWR;
-    bdrv_flags |= bdrv_is_snapshot(bs) ? BDRV_O_SNAPSHOT : 0;
+    bdrv_flags = blk_is_read_only(blk) ? 0 : BDRV_O_RDWR;
+    bdrv_flags |= blk_get_root_state(blk)->open_flags & ~BDRV_O_RDWR;
 
-    qmp_bdrv_open_encrypted(bs, filename, bdrv_flags, format, NULL, errp);
+    qmp_bdrv_open_encrypted(&bs, filename, bdrv_flags, format, NULL, &err);
+    if (err) {
+        error_propagate(errp, err);
+    } else if (new_bs) {
+        blk_insert_bs(blk, bs);
+        /* Has been sent automatically by bdrv_open() if blk_bs(blk) was not
+         * NULL */
+        blk_dev_change_media_cb(blk, true);
+    }
 
 out:
     aio_context_release(aio_context);
@@ -1975,7 +2001,15 @@  void qmp_block_set_io_throttle(const char *device, int64_t bps, int64_t bps_rd,
                   "Device '%s' not found", device);
         return;
     }
+
+    aio_context = blk_get_aio_context(blk);
+    aio_context_acquire(aio_context);
+
     bs = blk_bs(blk);
+    if (!bs) {
+        error_setg(errp, "Device '%s' has no medium", device);
+        goto out;
+    }
 
     memset(&cfg, 0, sizeof(cfg));
     cfg.buckets[THROTTLE_BPS_TOTAL].avg = bps;
@@ -2010,12 +2044,9 @@  void qmp_block_set_io_throttle(const char *device, int64_t bps, int64_t bps_rd,
     }
 
     if (!check_throttle_config(&cfg, errp)) {
-        return;
+        goto out;
     }
 
-    aio_context = bdrv_get_aio_context(bs);
-    aio_context_acquire(aio_context);
-
     if (throttle_enabled(&cfg)) {
         /* Enable I/O limits if they're not enabled yet, otherwise
          * just update the throttling group. */
@@ -2031,6 +2062,7 @@  void qmp_block_set_io_throttle(const char *device, int64_t bps, int64_t bps_rd,
         bdrv_io_limits_disable(bs);
     }
 
+out:
     aio_context_release(aio_context);
 }
 
@@ -2143,7 +2175,6 @@  void hmp_drive_del(Monitor *mon, const QDict *qdict)
         error_report("Device '%s' not found", id);
         return;
     }
-    bs = blk_bs(blk);
 
     if (!blk_legacy_dinfo(blk)) {
         error_report("Deleting device added with blockdev-add"
@@ -2151,16 +2182,19 @@  void hmp_drive_del(Monitor *mon, const QDict *qdict)
         return;
     }
 
-    aio_context = bdrv_get_aio_context(bs);
+    aio_context = blk_get_aio_context(blk);
     aio_context_acquire(aio_context);
 
-    if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_DRIVE_DEL, &local_err)) {
+    bs = blk_bs(blk);
+    if (bs && bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_DRIVE_DEL, &local_err)) {
         error_report_err(local_err);
         aio_context_release(aio_context);
         return;
     }
 
-    bdrv_close(bs);
+    if (bs) {
+        bdrv_close(bs);
+    }
 
     /* if we have a device attached to this BlockDriverState
      * then we need to make the drive anonymous until the device
@@ -2293,11 +2327,16 @@  void qmp_block_stream(const char *device,
                   "Device '%s' not found", device);
         return;
     }
-    bs = blk_bs(blk);
 
-    aio_context = bdrv_get_aio_context(bs);
+    aio_context = blk_get_aio_context(blk);
     aio_context_acquire(aio_context);
 
+    if (!blk_is_available(blk)) {
+        error_setg(errp, "Device '%s' has no medium", device);
+        goto out;
+    }
+    bs = blk_bs(blk);
+
     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_STREAM, errp)) {
         goto out;
     }
@@ -2368,11 +2407,16 @@  void qmp_block_commit(const char *device,
                   "Device '%s' not found", device);
         return;
     }
-    bs = blk_bs(blk);
 
-    aio_context = bdrv_get_aio_context(bs);
+    aio_context = blk_get_aio_context(blk);
     aio_context_acquire(aio_context);
 
+    if (!blk_is_available(blk)) {
+        error_setg(errp, "Device '%s' has no medium", device);
+        goto out;
+    }
+    bs = blk_bs(blk);
+
     if (bdrv_op_is_blocked(bs, BLOCK_OP_TYPE_COMMIT_SOURCE, errp)) {
         goto out;
     }
@@ -2478,17 +2522,17 @@  void qmp_drive_backup(const char *device, const char *target,
                   "Device '%s' not found", device);
         return;
     }
-    bs = blk_bs(blk);
 
-    aio_context = bdrv_get_aio_context(bs);
+    aio_context = blk_get_aio_context(blk);
     aio_context_acquire(aio_context);
 
     /* Although backup_run has this check too, we need to use bs->drv below, so
      * do an early check redundantly. */
-    if (!bdrv_is_inserted(bs)) {
+    if (!blk_is_available(blk)) {
         error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
         goto out;
     }
+    bs = blk_bs(blk);
 
     if (!has_format) {
         format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
@@ -2585,7 +2629,7 @@  void qmp_blockdev_backup(const char *device, const char *target,
                          BlockdevOnError on_target_error,
                          Error **errp)
 {
-    BlockBackend *blk;
+    BlockBackend *blk, *target_blk;
     BlockDriverState *bs;
     BlockDriverState *target_bs;
     Error *local_err = NULL;
@@ -2606,17 +2650,27 @@  void qmp_blockdev_backup(const char *device, const char *target,
         error_setg(errp, "Device '%s' not found", device);
         return;
     }
-    bs = blk_bs(blk);
 
-    aio_context = bdrv_get_aio_context(bs);
+    aio_context = blk_get_aio_context(blk);
     aio_context_acquire(aio_context);
 
-    blk = blk_by_name(target);
-    if (!blk) {
+    if (!blk_is_available(blk)) {
+        error_setg(errp, "Device '%s' has no medium", device);
+        goto out;
+    }
+    bs = blk_bs(blk);
+
+    target_blk = blk_by_name(target);
+    if (!target_blk) {
         error_setg(errp, "Device '%s' not found", target);
         goto out;
     }
-    target_bs = blk_bs(blk);
+
+    if (!blk_is_available(target_blk)) {
+        error_setg(errp, "Device '%s' has no medium", target);
+        goto out;
+    }
+    target_bs = blk_bs(target_blk);
 
     bdrv_ref(target_bs);
     bdrv_set_aio_context(target_bs, aio_context);
@@ -2693,15 +2747,15 @@  void qmp_drive_mirror(const char *device, const char *target,
                   "Device '%s' not found", device);
         return;
     }
-    bs = blk_bs(blk);
 
-    aio_context = bdrv_get_aio_context(bs);
+    aio_context = blk_get_aio_context(blk);
     aio_context_acquire(aio_context);
 
-    if (!bdrv_is_inserted(bs)) {
+    if (!blk_is_available(blk)) {
         error_setg(errp, QERR_DEVICE_HAS_NO_MEDIUM, device);
         goto out;
     }
+    bs = blk_bs(blk);
 
     if (!has_format) {
         format = mode == NEW_IMAGE_MODE_EXISTING ? NULL : bs->drv->format_name;
@@ -2831,17 +2885,22 @@  static BlockJob *find_block_job(const char *device, AioContext **aio_context,
     BlockBackend *blk;
     BlockDriverState *bs;
 
+    *aio_context = NULL;
+
     blk = blk_by_name(device);
     if (!blk) {
         goto notfound;
     }
-    bs = blk_bs(blk);
 
-    *aio_context = bdrv_get_aio_context(bs);
+    *aio_context = blk_get_aio_context(blk);
     aio_context_acquire(*aio_context);
 
+    if (!blk_is_available(blk)) {
+        goto notfound;
+    }
+    bs = blk_bs(blk);
+
     if (!bs->job) {
-        aio_context_release(*aio_context);
         goto notfound;
     }
 
@@ -2850,7 +2909,10 @@  static BlockJob *find_block_job(const char *device, AioContext **aio_context,
 notfound:
     error_set(errp, ERROR_CLASS_DEVICE_NOT_ACTIVE,
               "No active block job on device '%s'", device);
-    *aio_context = NULL;
+    if (*aio_context) {
+        aio_context_release(*aio_context);
+        *aio_context = NULL;
+    }
     return NULL;
 }
 
@@ -2957,11 +3019,16 @@  void qmp_change_backing_file(const char *device,
                   "Device '%s' not found", device);
         return;
     }
-    bs = blk_bs(blk);
 
-    aio_context = bdrv_get_aio_context(bs);
+    aio_context = blk_get_aio_context(blk);
     aio_context_acquire(aio_context);
 
+    if (!blk_is_available(blk)) {
+        error_setg(errp, "Device '%s' has no medium", device);
+        goto out;
+    }
+    bs = blk_bs(blk);
+
     image_bs = bdrv_lookup_bs(NULL, image_node_name, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c
index 36d7398..1bbc111 100644
--- a/hw/block/xen_disk.c
+++ b/hw/block/xen_disk.c
@@ -931,9 +931,11 @@  static int blk_connect(struct XenDevice *xendev)
     blk_attach_dev_nofail(blkdev->blk, blkdev);
     blkdev->file_size = blk_getlength(blkdev->blk);
     if (blkdev->file_size < 0) {
+        BlockDriverState *bs = blk_bs(blkdev->blk);
+        const char *drv_name = bs ? bdrv_get_format_name(bs) : NULL;
         xen_be_printf(&blkdev->xendev, 1, "blk_getlength: %d (%s) | drv %s\n",
                       (int)blkdev->file_size, strerror(-blkdev->file_size),
-                      bdrv_get_format_name(blk_bs(blkdev->blk)) ?: "-");
+                      drv_name ?: "-");
         blkdev->file_size = 0;
     }
 
diff --git a/migration/block.c b/migration/block.c
index ed865ed..f7bb1e0 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -808,6 +808,11 @@  static int block_load(QEMUFile *f, void *opaque, int version_id)
                 return -EINVAL;
             }
             bs = blk_bs(blk);
+            if (!bs) {
+                fprintf(stderr, "Block device %s has no medium\n",
+                        device_name);
+                return -EINVAL;
+            }
 
             if (bs != bs_prev) {
                 bs_prev = bs;
diff --git a/monitor.c b/monitor.c
index 1f43263..94b7267 100644
--- a/monitor.c
+++ b/monitor.c
@@ -4130,6 +4130,10 @@  int monitor_read_block_device_key(Monitor *mon, const char *device,
         monitor_printf(mon, "Device not found %s\n", device);
         return -1;
     }
+    if (!blk_bs(blk)) {
+        monitor_printf(mon, "Device '%s' has no medium\n", device);
+        return -1;
+    }
 
     bdrv_add_key(blk_bs(blk), NULL, &err);
     if (err) {