xen-blkfront: Handle discard requests.

If the backend advertises 'feature-discard', then interrogate
the backend for alignment and granularity. Setup the request
queue with the appropiate values and send the discard operation
as required.

Signed-off-by: Li Dongyang <lidongyang@novell.com>
[v1: Amended commit description]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 88 insertions, 23 deletions

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index b536a9cef917..52076b0d0326 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -98,6 +98,9 @@ struct blkfront_info
         unsigned long shadow_free;
         unsigned int feature_flush;
         unsigned int flush_op;
+        unsigned int feature_discard;
+        unsigned int discard_granularity;
+        unsigned int discard_alignment;
         int is_ready;
 };
 
@@ -302,29 +305,36 @@ static int blkif_queue_request(struct request *req)
                 ring_req->operation = info->flush_op;
         }
 
-        ring_req->nr_segments = blk_rq_map_sg(req->q, req, info->sg);
-        BUG_ON(ring_req->nr_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
+        if (unlikely(req->cmd_flags & REQ_DISCARD)) {
+                /* id, sector_number and handle are set above. */
+                ring_req->operation = BLKIF_OP_DISCARD;
+                ring_req->nr_segments = 0;
+                ring_req->u.discard.nr_sectors = blk_rq_sectors(req);
+        } else {
+                ring_req->nr_segments = blk_rq_map_sg(req->q, req, info->sg);
+                BUG_ON(ring_req->nr_segments > BLKIF_MAX_SEGMENTS_PER_REQUEST);
 
-        for_each_sg(info->sg, sg, ring_req->nr_segments, i) {
-                buffer_mfn = pfn_to_mfn(page_to_pfn(sg_page(sg)));
-                fsect = sg->offset >> 9;
-                lsect = fsect + (sg->length >> 9) - 1;
-                /* install a grant reference. */
-                ref = gnttab_claim_grant_reference(&gref_head);
-                BUG_ON(ref == -ENOSPC);
+                for_each_sg(info->sg, sg, ring_req->nr_segments, i) {
+                        buffer_mfn = pfn_to_mfn(page_to_pfn(sg_page(sg)));
+                        fsect = sg->offset >> 9;
+                        lsect = fsect + (sg->length >> 9) - 1;
+                        /* install a grant reference. */
+                        ref = gnttab_claim_grant_reference(&gref_head);
+                        BUG_ON(ref == -ENOSPC);
 
-                gnttab_grant_foreign_access_ref(
-                                ref,
-                                info->xbdev->otherend_id,
-                                buffer_mfn,
-                                rq_data_dir(req) );
-
-                info->shadow[id].frame[i] = mfn_to_pfn(buffer_mfn);
-                ring_req->u.rw.seg[i] =
-                                (struct blkif_request_segment) {
-                                        .gref       = ref,
-                                        .first_sect = fsect,
-                                        .last_sect  = lsect };
+                        gnttab_grant_foreign_access_ref(
+                                        ref,
+                                        info->xbdev->otherend_id,
+                                        buffer_mfn,
+                                        rq_data_dir(req));
+
+                        info->shadow[id].frame[i] = mfn_to_pfn(buffer_mfn);
+                        ring_req->u.rw.seg[i] =
+                                        (struct blkif_request_segment) {
+                                                .gref       = ref,
+                                                .first_sect = fsect,
+                                                .last_sect  = lsect };
+                }
         }
 
         info->ring.req_prod_pvt++;
@@ -399,6 +409,7 @@ wait:
 static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
 {
         struct request_queue *rq;
+        struct blkfront_info *info = gd->private_data;
 
         rq = blk_init_queue(do_blkif_request, &blkif_io_lock);
         if (rq == NULL)
@@ -406,6 +417,13 @@ static int xlvbd_init_blk_queue(struct gendisk *gd, u16 sector_size)
 
         queue_flag_set_unlocked(QUEUE_FLAG_VIRT, rq);
 
+        if (info->feature_discard) {
+                queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, rq);
+                blk_queue_max_discard_sectors(rq, get_capacity(gd));
+                rq->limits.discard_granularity = info->discard_granularity;
+                rq->limits.discard_alignment = info->discard_alignment;
+        }
+
         /* Hard sector size and max sectors impersonate the equiv. hardware. */
         blk_queue_logical_block_size(rq, sector_size);
         blk_queue_max_hw_sectors(rq, 512);
@@ -722,6 +740,19 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 
                 error = (bret->status == BLKIF_RSP_OKAY) ? 0 : -EIO;
                 switch (bret->operation) {
+                case BLKIF_OP_DISCARD:
+                        if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
+                                struct request_queue *rq = info->rq;
+                                printk(KERN_WARNING "blkfront: %s: discard op failed\n",
+                                           info->gd->disk_name);
+                                error = -EOPNOTSUPP;
+                                info->feature_discard = 0;
+                                spin_lock(rq->queue_lock);
+                                queue_flag_clear(QUEUE_FLAG_DISCARD, rq);
+                                spin_unlock(rq->queue_lock);
+                        }
+                        __blk_end_request_all(req, error);
+                        break;
                 case BLKIF_OP_FLUSH_DISKCACHE:
                 case BLKIF_OP_WRITE_BARRIER:
                         if (unlikely(bret->status == BLKIF_RSP_EOPNOTSUPP)) {
@@ -1098,6 +1129,33 @@ blkfront_closing(struct blkfront_info *info)
         bdput(bdev);
 }
 
+static void blkfront_setup_discard(struct blkfront_info *info)
+{
+        int err;
+        char *type;
+        unsigned int discard_granularity;
+        unsigned int discard_alignment;
+
+        type = xenbus_read(XBT_NIL, info->xbdev->otherend, "type", NULL);
+        if (IS_ERR(type))
+                return;
+
+        if (strncmp(type, "phy", 3) == 0) {
+                err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+                        "discard-granularity", "%u", &discard_granularity,
+                        "discard-alignment", "%u", &discard_alignment,
+                        NULL);
+                if (!err) {
+                        info->feature_discard = 1;
+                        info->discard_granularity = discard_granularity;
+                        info->discard_alignment = discard_alignment;
+                }
+        } else if (strncmp(type, "file", 4) == 0)
+                info->feature_discard = 1;
+
+        kfree(type);
+}
+
 /*
  * Invoked when the backend is finally 'ready' (and has told produced
  * the details about the physical device - #sectors, size, etc).
@@ -1108,7 +1166,7 @@ static void blkfront_connect(struct blkfront_info *info)
         unsigned long sector_size;
         unsigned int binfo;
         int err;
-        int barrier, flush;
+        int barrier, flush, discard;
 
         switch (info->connected) {
         case BLKIF_STATE_CONNECTED:
@@ -1178,7 +1236,14 @@ static void blkfront_connect(struct blkfront_info *info)
                 info->feature_flush = REQ_FLUSH;
                 info->flush_op = BLKIF_OP_FLUSH_DISKCACHE;
         }
-                
+
+        err = xenbus_gather(XBT_NIL, info->xbdev->otherend,
+                            "feature-discard", "%d", &discard,
+                            NULL);
+
+        if (!err && discard)
+                blkfront_setup_discard(info);
+
         err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size);
         if (err) {
                 xenbus_dev_fatal(info->xbdev, err, "xlvbd_add at %s",