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From: Markus Armbruster <armbru@redhat.com>
References: <1472767012-7641-1-git-send-email-jsnow@redhat.com>
	<1472767012-7641-2-git-send-email-jsnow@redhat.com>
Date: Fri, 02 Sep 2016 07:44:20 +0200
In-Reply-To: <1472767012-7641-2-git-send-email-jsnow@redhat.com> (John Snow's
	message of "Thu, 1 Sep 2016 17:56:52 -0400")
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Subject: Re: [Qemu-devel] [PATCH v2 1/1] block-backend: allow flush on
 devices with open tray
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To: John Snow <jsnow@redhat.com>
Cc: qemu-block@nongnu.org, kwolf@redhat.com, mreitz@redhat.com, qemu-devel@nongnu.org, qemu-stable@nongnu.org

John Snow <jsnow@redhat.com> writes:

> If a device still has an attached BDS because the medium has not yet
> been removed, we will be unable to migrate to a new host because
> blk_flush will return an error for that backend.
>
> Replace the call to blk_is_available to blk_is_inserted to weaken
> the check and allow flushes from the backend to work, while still
> disallowing flushes from the frontend/device model to work.
>
> This fixes a regression present in 2.6.0 caused by the following commit:
> fe1a9cbc339bb54d20f1ca4c1e8788d16944d5cf
> block: Move some bdrv_*_all() functions to BB
>
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  block/block-backend.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/block/block-backend.c b/block/block-backend.c
> index effa038..36a32c3 100644
> --- a/block/block-backend.c
> +++ b/block/block-backend.c
> @@ -1058,7 +1058,7 @@ BlockAIOCB *blk_aio_pwritev(BlockBackend *blk, int64_t offset,
>  BlockAIOCB *blk_aio_flush(BlockBackend *blk,
>                            BlockCompletionFunc *cb, void *opaque)
>  {
> -    if (!blk_is_available(blk)) {
> +    if (!blk_is_inserted(blk)) {
>          return blk_abort_aio_request(blk, cb, opaque, -ENOMEDIUM);
>      }
>  
> @@ -1118,7 +1118,7 @@ int blk_co_pdiscard(BlockBackend *blk, int64_t offset, int count)
>  
>  int blk_co_flush(BlockBackend *blk)
>  {
> -    if (!blk_is_available(blk)) {
> +    if (!blk_is_inserted(blk)) {
>          return -ENOMEDIUM;
>      }
>  
> @@ -1127,7 +1127,7 @@ int blk_co_flush(BlockBackend *blk)
>  
>  int blk_flush(BlockBackend *blk)
>  {
> -    if (!blk_is_available(blk)) {
> +    if (!blk_is_inserted(blk)) {
>          return -ENOMEDIUM;
>      }

Naive question: should we flush before we open the tray?