>>> On 09.09.11 at 20:31, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:
> By default we would set the info->flush_op=0, and zero maps
> to BLKIF_OP_READ request code. So if the backend did not support
> either barrier ('feature-barrier') or flush ('feature-flush-cache')
> we would end up using that opcode for the flush/barrier request, meaning
> we actually do a READ request. Fortunatly for us, __generic_make_request
> checks q->flush_flags and realizes that we don't do FLUSH and removes
> the REQ_FLUSH | REQ_FUA so we never end up issuing a READ request
> for a flush request. However, other third party implementations of
> __make_request might not be so smart, so lets fix this up.
Wouldn't it be better to simply have blkif_queue_request() fail in that
case (and then it doesn't matter whether flush_op is set to 0 or -1)?
Not the least because older (forward-port) backends stall the incoming
queue and are possibly verbose for invalid requests seen.
Jan
> CC: stable@xxxxxxxxxx
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
> drivers/block/xen-blkfront.c | 8 ++++----
> 1 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index e205d91..c4aa9da 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -97,7 +97,7 @@ struct blkfront_info
> struct blk_shadow shadow[BLK_RING_SIZE];
> unsigned long shadow_free;
> unsigned int feature_flush;
> - unsigned int flush_op;
> + int flush_op;
> unsigned int feature_discard;
> unsigned int discard_granularity;
> unsigned int discard_alignment;
> @@ -774,7 +774,7 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
> if (error == -EOPNOTSUPP)
> error = 0;
> info->feature_flush = 0;
> - info->flush_op = 0;
> + info->flush_op = -1; /* 0 is BLKIF_OP_READ */
> xlvbd_flush(info);
> }
> /* fall through */
> @@ -1207,7 +1207,7 @@ static void blkfront_connect(struct blkfront_info
> *info)
> }
>
> info->feature_flush = 0;
> - info->flush_op = 0;
> + info->flush_op = -1; /* 0 is BLKIF_OP_READ */
>
> err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
> "feature-barrier", "%d", &barrier,
> @@ -1234,7 +1234,7 @@ static void blkfront_connect(struct blkfront_info
> *info)
> if (!err && flush)
> info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
>
> - if (info->flush_op)
> + if (info->flush_op > 0)
> info->feature_flush = REQ_FLUSH | REQ_FUA;
>
> err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
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