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SubjectRe: [PATCH] xen/blkfront: remove redundant flush_op
On 12/08/2014 09:17 AM, Vitaly Kuznetsov wrote:
> flush_op is unambiguously defined by feature_flush:
> REQ_FUA | REQ_FLUSH -> BLKIF_OP_WRITE_BARRIER
> REQ_FLUSH -> BLKIF_OP_FLUSH_DISKCACHE
> 0 -> 0
> and thus can be removed. This is just a cleanup.
>
> The patch was suggested by Boris Ostrovsky.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> The patch is supposed to be applied after "xen/blkfront: improve protection
> against issuing unsupported REQ_FUA".
> ---
> drivers/block/xen-blkfront.c | 24 ++++++++++++------------
> 1 file changed, 12 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 2e6c103..d1ee233 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -126,7 +126,6 @@ struct blkfront_info
> unsigned int persistent_gnts_c;
> unsigned long shadow_free;
> unsigned int feature_flush;
> - unsigned int flush_op;
> unsigned int feature_discard:1;
> unsigned int feature_secdiscard:1;
> unsigned int discard_granularity;
> @@ -479,7 +478,14 @@ static int blkif_queue_request(struct request *req)
> * way. (It's also a FLUSH+FUA, since it is
> * guaranteed ordered WRT previous writes.)
> */
> - ring_req->operation = info->flush_op;
> + if (unlikely(info->feature_flush & REQ_FUA))
> + ring_req->operation =
> + BLKIF_OP_WRITE_BARRIER;
> + else if (likely(info->feature_flush))
> + ring_req->operation =
> + BLKIF_OP_FLUSH_DISKCACHE;

To better future-proof it against new flags maybe something like

switch ( info->feature_flush & (REQ_FLUSH|REQ_FUA) ) {
case REQ_FLUSH|REQ_FUA: ...
case REQ_FLUSH: ...
default: ...

or the if/else equivalent?


> + else
> + ring_req->operation = 0;
> }
> ring_req->u.rw.nr_segments = nseg;
> }
> @@ -691,8 +697,8 @@ static void xlvbd_flush(struct blkfront_info *info)
> blk_queue_flush(info->rq, info->feature_flush);
> printk(KERN_INFO "blkfront: %s: %s: %s %s %s %s %s\n",
> info->gd->disk_name,
> - info->flush_op == BLKIF_OP_WRITE_BARRIER ?
> - "barrier" : (info->flush_op == BLKIF_OP_FLUSH_DISKCACHE ?
> + info->feature_flush == (REQ_FLUSH | REQ_FUA) ?
> + "barrier" : (info->feature_flush == REQ_FLUSH ?

And something similar here?

Thanks.
-boris


> "flush diskcache" : "barrier or flush"),
> info->feature_flush ? "enabled;" : "disabled;",
> "persistent grants:",
> @@ -1190,7 +1196,6 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
> if (error == -EOPNOTSUPP)
> error = 0;
> info->feature_flush = 0;
> - info->flush_op = 0;
> xlvbd_flush(info);
> }
> /* fall through */
> @@ -1810,7 +1815,6 @@ static void blkfront_connect(struct blkfront_info *info)
> physical_sector_size = sector_size;
>
> info->feature_flush = 0;
> - info->flush_op = 0;
>
> err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
> "feature-barrier", "%d", &barrier,
> @@ -1823,10 +1827,8 @@ static void blkfront_connect(struct blkfront_info *info)
> *
> * If there are barriers, then we use flush.
> */
> - if (!err && barrier) {
> + if (!err && barrier)
> info->feature_flush = REQ_FLUSH | REQ_FUA;
> - info->flush_op = BLKIF_OP_WRITE_BARRIER;
> - }
> /*
> * And if there is "feature-flush-cache" use that above
> * barriers.
> @@ -1835,10 +1837,8 @@ static void blkfront_connect(struct blkfront_info *info)
> "feature-flush-cache", "%d", &flush,
> NULL);
>
> - if (!err && flush) {
> + if (!err && flush)
> info->feature_flush = REQ_FLUSH;
> - info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
> - }
>
> err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
> "feature-discard", "%d", &discard,



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