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xen/blkfront: Use QUEUE_ORDERED_DRAIN for old backends 

If there's no feature-barrier key in xenstore, then it means its a fairly
old backend which does uncached in-order writes, which means ORDERED_DRAIN
is appropriate.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
This commit is contained in:
Jeremy Fitzhardinge 2010-07-28 10:49:29 -07:00 committed by Jens Axboe
parent 4dab46ff26
commit 7901d14144
1 changed files with 29 additions and 16 deletions
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45
drivers/block/xen-blkfront.c
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@ -420,26 +420,22 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
static int xlvbd_barrier(struct blkfront_info *info)
{
int err;
unsigned ordered = QUEUE_ORDERED_NONE;
const char *barrier;
/*
* If we don't have barrier support, then there's really no
* way to guarantee write ordering, so we really just have to
* send writes to the backend and hope for the best. If
* barriers are supported then we can treat them as proper
* ordering tags.
*/
if (info->feature_barrier)
ordered = QUEUE_ORDERED_TAG;
switch (info->feature_barrier) {
case QUEUE_ORDERED_DRAIN: barrier = "enabled (drain)"; break;
case QUEUE_ORDERED_TAG: barrier = "enabled (tag)"; break;
case QUEUE_ORDERED_NONE: barrier = "disabled"; break;
default: return -EINVAL;
}
err = blk_queue_ordered(info->rq, ordered);
err = blk_queue_ordered(info->rq, info->feature_barrier);
if (err)
return err;
printk(KERN_INFO "blkfront: %s: barriers %s\n",
info->gd->disk_name,
info->feature_barrier ? "enabled" : "disabled");
info->gd->disk_name, barrier);
return 0;
}
@ -665,7 +661,7 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
printk(KERN_WARNING "blkfront: %s: write barrier op failed\n",
info->gd->disk_name);
error = -EOPNOTSUPP;
info->feature_barrier = 0;
info->feature_barrier = QUEUE_ORDERED_NONE;
xlvbd_barrier(info);
}
/* fall through */
@ -1003,6 +999,7 @@ static void blkfront_connect(struct blkfront_info *info)
unsigned long sector_size;
unsigned int binfo;
int err;
int barrier;
switch (info->connected) {
case BLKIF_STATE_CONNECTED:
@ -1043,10 +1040,26 @@ static void blkfront_connect(struct blkfront_info *info)
}
err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
"feature-barrier", "%lu", &info->feature_barrier,
"feature-barrier", "%lu", &barrier,
NULL);
/*
* If there's no "feature-barrier" defined, then it means
* we're dealing with a very old backend which writes
* synchronously; draining will do what needs to get done.
*
* If there are barriers, then we can do full queued writes
* with tagged barriers.
*
* If barriers are not supported, then there's no much we can
* do, so just set ordering to NONE.
*/
if (err)
info->feature_barrier = 0;
info->feature_barrier = QUEUE_ORDERED_DRAIN;
else if (barrier)
info->feature_barrier = QUEUE_ORDERED_TAG;
else
info->feature_barrier = QUEUE_ORDERED_NONE;
err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
if (err) {