From: Kevin Wolf <kwolf@redhat.com>

The "inactive" state of BDS affects whether the permissions can be
granted, we must call bdrv_invalidate_cache before bdrv_set_perm to
support "-incoming defer" case.

Reported-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
Signed-off-by: Fam Zheng <famz@redhat.com>
---
 nbd/server.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index 82a78bf439..b68b6fb535 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1045,11 +1045,22 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset, off_t size,
                           bool writethrough, BlockBackend *on_eject_blk,
                           Error **errp)
 {
+    AioContext  *ctx;
     BlockBackend *blk;
     NBDExport *exp = g_malloc0(sizeof(NBDExport));
     uint64_t perm;
     int ret;
 
+    /*
+     * NBD exports are used for non-shared storage migration.  Make sure
+     * that BDRV_O_INACTIVE is cleared and the image is ready for write
+     * access since the export could be available before migration handover.
+     */
+    ctx = bdrv_get_aio_context(bs);
+    aio_context_acquire(ctx);
+    bdrv_invalidate_cache(bs, NULL);
+    aio_context_release(ctx);
+
     /* Don't allow resize while the NBD server is running, otherwise we don't
      * care what happens with the node. */
     perm = BLK_PERM_CONSISTENT_READ;
@@ -1087,15 +1098,6 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset, off_t size,
         exp->eject_notifier.notify = nbd_eject_notifier;
         blk_add_remove_bs_notifier(on_eject_blk, &exp->eject_notifier);
     }
-
-    /*
-     * NBD exports are used for non-shared storage migration.  Make sure
-     * that BDRV_O_INACTIVE is cleared and the image is ready for write
-     * access since the export could be available before migration handover.
-     */
-    aio_context_acquire(exp->ctx);
-    blk_invalidate_cache(blk, NULL);
-    aio_context_release(exp->ctx);
     return exp;
 
 fail:
-- 
2.13.4

On 08/15/2017 08:07 AM, Fam Zheng wrote:
> From: Kevin Wolf <kwolf@redhat.com>
> 
> The "inactive" state of BDS affects whether the permissions can be
> granted, we must call bdrv_invalidate_cache before bdrv_set_perm to
> support "-incoming defer" case.
> 
> Reported-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  nbd/server.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> diff --git a/nbd/server.c b/nbd/server.c
> index 82a78bf439..b68b6fb535 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -1045,11 +1045,22 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset, off_t size,
>                            bool writethrough, BlockBackend *on_eject_blk,
>                            Error **errp)
>  {
> +    AioContext  *ctx;

Odd spacing; can fix up as maintainer.

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org