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 <[email protected]>
---
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;
+ 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 ?
"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,
--
1.9.3
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 <[email protected]>
> ---
> 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,
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 <[email protected]>
---
Changes from v1:
Future-proof feature_flush against new flags [Boris Ostrovsky].
The patch is supposed to be applied after "xen/blkfront: improve protection
against issuing unsupported REQ_FUA".
---
drivers/block/xen-blkfront.c | 51 +++++++++++++++++++++++++++-----------------
1 file changed, 31 insertions(+), 20 deletions(-)
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 2e6c103..2236c6f 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 +478,19 @@ 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;
+ switch (info->feature_flush &
+ ((REQ_FLUSH|REQ_FUA))) {
+ case REQ_FLUSH|REQ_FUA:
+ ring_req->operation =
+ BLKIF_OP_WRITE_BARRIER;
+ break;
+ case REQ_FLUSH:
+ ring_req->operation =
+ BLKIF_OP_FLUSH_DISKCACHE;
+ break;
+ default:
+ ring_req->operation = 0;
+ }
}
ring_req->u.rw.nr_segments = nseg;
}
@@ -685,20 +696,26 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
return 0;
}
+static const char *flush_info(unsigned int feature_flush)
+{
+ switch (feature_flush & ((REQ_FLUSH | REQ_FUA))) {
+ case REQ_FLUSH|REQ_FUA:
+ return "barrier: enabled;";
+ case REQ_FLUSH:
+ return "flush diskcache: enabled;";
+ default:
+ return "barrier or flush: disabled;";
+ }
+}
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 ?
- "flush diskcache" : "barrier or flush"),
- info->feature_flush ? "enabled;" : "disabled;",
- "persistent grants:",
- info->feature_persistent ? "enabled;" : "disabled;",
- "indirect descriptors:",
- info->max_indirect_segments ? "enabled;" : "disabled;");
+ pr_info("blkfront: %s: %s %s %s %s %s\n",
+ info->gd->disk_name, flush_info(info->feature_flush),
+ "persistent grants:", info->feature_persistent ?
+ "enabled;" : "disabled;", "indirect descriptors:",
+ info->max_indirect_segments ? "enabled;" : "disabled;");
}
static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
@@ -1190,7 +1207,6 @@ 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 +1826,6 @@ 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 +1838,8 @@ 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 +1848,8 @@ 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,
--
1.9.3
On 12/09/2014 09:25 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 <[email protected]>
Reviewed-by: Boris Ostrovsky <[email protected]>
> ---
> Changes from v1:
> Future-proof feature_flush against new flags [Boris Ostrovsky].
>
> The patch is supposed to be applied after "xen/blkfront: improve protection
> against issuing unsupported REQ_FUA".
> ---
> drivers/block/xen-blkfront.c | 51 +++++++++++++++++++++++++++-----------------
> 1 file changed, 31 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index 2e6c103..2236c6f 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 +478,19 @@ 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;
> + switch (info->feature_flush &
> + ((REQ_FLUSH|REQ_FUA))) {
> + case REQ_FLUSH|REQ_FUA:
> + ring_req->operation =
> + BLKIF_OP_WRITE_BARRIER;
> + break;
> + case REQ_FLUSH:
> + ring_req->operation =
> + BLKIF_OP_FLUSH_DISKCACHE;
> + break;
> + default:
> + ring_req->operation = 0;
> + }
> }
> ring_req->u.rw.nr_segments = nseg;
> }
> @@ -685,20 +696,26 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
> return 0;
> }
>
> +static const char *flush_info(unsigned int feature_flush)
> +{
> + switch (feature_flush & ((REQ_FLUSH | REQ_FUA))) {
> + case REQ_FLUSH|REQ_FUA:
> + return "barrier: enabled;";
> + case REQ_FLUSH:
> + return "flush diskcache: enabled;";
> + default:
> + return "barrier or flush: disabled;";
> + }
> +}
>
> 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 ?
> - "flush diskcache" : "barrier or flush"),
> - info->feature_flush ? "enabled;" : "disabled;",
> - "persistent grants:",
> - info->feature_persistent ? "enabled;" : "disabled;",
> - "indirect descriptors:",
> - info->max_indirect_segments ? "enabled;" : "disabled;");
> + pr_info("blkfront: %s: %s %s %s %s %s\n",
> + info->gd->disk_name, flush_info(info->feature_flush),
> + "persistent grants:", info->feature_persistent ?
> + "enabled;" : "disabled;", "indirect descriptors:",
> + info->max_indirect_segments ? "enabled;" : "disabled;");
> }
>
> static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
> @@ -1190,7 +1207,6 @@ 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 +1826,6 @@ 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 +1838,8 @@ 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 +1848,8 @@ 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,
On Tue, Dec 09, 2014 at 03:56:46PM -0500, Boris Ostrovsky wrote:
> On 12/09/2014 09:25 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 <[email protected]>
>
>
> Reviewed-by: Boris Ostrovsky <[email protected]>
Thank you.
I am testing this and the xen/blkfront: improve protection against issuing unsupported REQ_FUA
right now for 3.19
>
>
> >---
> >Changes from v1:
> > Future-proof feature_flush against new flags [Boris Ostrovsky].
> >
> >The patch is supposed to be applied after "xen/blkfront: improve protection
> >against issuing unsupported REQ_FUA".
> >---
> > drivers/block/xen-blkfront.c | 51 +++++++++++++++++++++++++++-----------------
> > 1 file changed, 31 insertions(+), 20 deletions(-)
> >
> >diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> >index 2e6c103..2236c6f 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 +478,19 @@ 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;
> >+ switch (info->feature_flush &
> >+ ((REQ_FLUSH|REQ_FUA))) {
> >+ case REQ_FLUSH|REQ_FUA:
> >+ ring_req->operation =
> >+ BLKIF_OP_WRITE_BARRIER;
> >+ break;
> >+ case REQ_FLUSH:
> >+ ring_req->operation =
> >+ BLKIF_OP_FLUSH_DISKCACHE;
> >+ break;
> >+ default:
> >+ ring_req->operation = 0;
> >+ }
> > }
> > ring_req->u.rw.nr_segments = nseg;
> > }
> >@@ -685,20 +696,26 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size,
> > return 0;
> > }
> >+static const char *flush_info(unsigned int feature_flush)
> >+{
> >+ switch (feature_flush & ((REQ_FLUSH | REQ_FUA))) {
> >+ case REQ_FLUSH|REQ_FUA:
> >+ return "barrier: enabled;";
> >+ case REQ_FLUSH:
> >+ return "flush diskcache: enabled;";
> >+ default:
> >+ return "barrier or flush: disabled;";
> >+ }
> >+}
> > 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 ?
> >- "flush diskcache" : "barrier or flush"),
> >- info->feature_flush ? "enabled;" : "disabled;",
> >- "persistent grants:",
> >- info->feature_persistent ? "enabled;" : "disabled;",
> >- "indirect descriptors:",
> >- info->max_indirect_segments ? "enabled;" : "disabled;");
> >+ pr_info("blkfront: %s: %s %s %s %s %s\n",
> >+ info->gd->disk_name, flush_info(info->feature_flush),
> >+ "persistent grants:", info->feature_persistent ?
> >+ "enabled;" : "disabled;", "indirect descriptors:",
> >+ info->max_indirect_segments ? "enabled;" : "disabled;");
> > }
> > static int xen_translate_vdev(int vdevice, int *minor, unsigned int *offset)
> >@@ -1190,7 +1207,6 @@ 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 +1826,6 @@ 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 +1838,8 @@ 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 +1848,8 @@ 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,
>