xen/blkfront: pseudo support for multi hardware queues/rings

Preparatory patch for multiple hardware queues (rings). The number of
rings is unconditionally set to 1, larger number will be enabled in
patch "xen/blkfront: negotiate number of queues/rings to be used with backend"
so as to make review easier.

Note that blkfront_gather_backend_features does not call
blkfront_setup_indirect anymore (as that needs to be done per ring).
That means that in blkif_recover/blkif_connect we have to do it in a loop
(bounded by nr_rings).

Signed-off-by: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

1 files changed, 198 insertions, 145 deletions

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 0c3ad214a792..0638b1722a40 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -150,6 +150,7 @@ struct blkfront_info
         int vdevice;
         blkif_vdev_t handle;
         enum blkif_state connected;
+        /* Number of pages per ring buffer. */
         unsigned int nr_ring_pages;
         struct request_queue *rq;
         struct list_head grants;
@@ -164,7 +165,8 @@ struct blkfront_info
         unsigned int max_indirect_segments;
         int is_ready;
         struct blk_mq_tag_set tag_set;
-        struct blkfront_ring_info rinfo;
+        struct blkfront_ring_info *rinfo;
+        unsigned int nr_rings;
 };
 
 static unsigned int nr_minors;
@@ -209,7 +211,7 @@ static DEFINE_SPINLOCK(minor_lock);
 #define GREFS(_psegs)   ((_psegs) * GRANTS_PER_PSEG)
 
 static int blkfront_setup_indirect(struct blkfront_ring_info *rinfo);
-static int blkfront_gather_backend_features(struct blkfront_info *info);
+static void blkfront_gather_backend_features(struct blkfront_info *info);
 
 static int get_id_from_freelist(struct blkfront_ring_info *rinfo)
 {
@@ -338,8 +340,8 @@ static struct grant *get_indirect_grant(grant_ref_t *gref_head,
                 struct page *indirect_page;
 
                 /* Fetch a pre-allocated page to use for indirect grefs */
-                BUG_ON(list_empty(&info->rinfo.indirect_pages));
-                indirect_page = list_first_entry(&info->rinfo.indirect_pages,
+                BUG_ON(list_empty(&info->rinfo->indirect_pages));
+                indirect_page = list_first_entry(&info->rinfo->indirect_pages,
                                                  struct page, lru);
                 list_del(&indirect_page->lru);
                 gnt_list_entry->page = indirect_page;
@@ -597,7 +599,6 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri
          * existing persistent grants, or if we have to get new grants,
          * as there are not sufficiently many free.
          */
-        bool new_persistent_gnts;
         struct scatterlist *sg;
         int num_sg, max_grefs, num_grant;
 
@@ -609,12 +610,12 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri
                  */
                 max_grefs += INDIRECT_GREFS(max_grefs);
 
-        /* Check if we have enough grants to allocate a requests */
-        if (info->persistent_gnts_c < max_grefs) {
-                new_persistent_gnts = 1;
-                if (gnttab_alloc_grant_references(
-                    max_grefs - info->persistent_gnts_c,
-                    &setup.gref_head) < 0) {
+        /*
+         * We have to reserve 'max_grefs' grants because persistent
+         * grants are shared by all rings.
+         */
+        if (max_grefs > 0)
+                if (gnttab_alloc_grant_references(max_grefs, &setup.gref_head) < 0) {
                         gnttab_request_free_callback(
                                 &rinfo->callback,
                                 blkif_restart_queue_callback,
@@ -622,8 +623,6 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri
                                 max_grefs);
                         return 1;
                 }
-        } else
-                new_persistent_gnts = 0;
 
         /* Fill out a communications ring structure. */
         ring_req = RING_GET_REQUEST(&rinfo->ring, rinfo->ring.req_prod_pvt);
@@ -712,7 +711,7 @@ static int blkif_queue_rw_req(struct request *req, struct blkfront_ring_info *ri
         /* Keep a private copy so we can reissue requests when recovering. */
         rinfo->shadow[id].req = *ring_req;
 
-        if (new_persistent_gnts)
+        if (max_grefs > 0)
                 gnttab_free_grant_references(setup.gref_head);
 
         return 0;
@@ -791,7 +790,8 @@ static int blk_mq_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
 {
         struct blkfront_info *info = (struct blkfront_info *)data;
 
-        hctx->driver_data = &info->rinfo;
+        BUG_ON(info->nr_rings <= index);
+        hctx->driver_data = &info->rinfo[index];
         return 0;
 }
 
@@ -1050,8 +1050,7 @@ static int xlvbd_alloc_gendisk(blkif_sector_t capacity,
 
 static void xlvbd_release_gendisk(struct blkfront_info *info)
 {
-        unsigned int minor, nr_minors;
-        struct blkfront_ring_info *rinfo = &info->rinfo;
+        unsigned int minor, nr_minors, i;
 
         if (info->rq == NULL)
                 return;
@@ -1059,11 +1058,15 @@ static void xlvbd_release_gendisk(struct blkfront_info *info)
         /* No more blkif_request(). */
         blk_mq_stop_hw_queues(info->rq);
 
-        /* No more gnttab callback work. */
-        gnttab_cancel_free_callback(&rinfo->callback);
+        for (i = 0; i < info->nr_rings; i++) {
+                struct blkfront_ring_info *rinfo = &info->rinfo[i];
 
-        /* Flush gnttab callback work. Must be done with no locks held. */
-        flush_work(&rinfo->work);
+                /* No more gnttab callback work. */
+                gnttab_cancel_free_callback(&rinfo->callback);
+
+                /* Flush gnttab callback work. Must be done with no locks held. */
+                flush_work(&rinfo->work);
+        }
 
         del_gendisk(info->gd);
 
@@ -1096,37 +1099,11 @@ static void blkif_restart_queue(struct work_struct *work)
         spin_unlock_irq(&rinfo->dev_info->io_lock);
 }
 
-static void blkif_free(struct blkfront_info *info, int suspend)
+static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 {
         struct grant *persistent_gnt;
-        struct grant *n;
+        struct blkfront_info *info = rinfo->dev_info;
         int i, j, segs;
-        struct blkfront_ring_info *rinfo = &info->rinfo;
-
-        /* Prevent new requests being issued until we fix things up. */
-        spin_lock_irq(&info->io_lock);
-        info->connected = suspend ?
-                BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
-        /* No more blkif_request(). */
-        if (info->rq)
-                blk_mq_stop_hw_queues(info->rq);
-
-        /* Remove all persistent grants */
-        if (!list_empty(&info->grants)) {
-                list_for_each_entry_safe(persistent_gnt, n,
-                                         &info->grants, node) {
-                        list_del(&persistent_gnt->node);
-                        if (persistent_gnt->gref != GRANT_INVALID_REF) {
-                                gnttab_end_foreign_access(persistent_gnt->gref,
-                                                          0, 0UL);
-                                info->persistent_gnts_c--;
-                        }
-                        if (info->feature_persistent)
-                                __free_page(persistent_gnt->page);
-                        kfree(persistent_gnt);
-                }
-        }
-        BUG_ON(info->persistent_gnts_c != 0);
 
         /*
          * Remove indirect pages, this only happens when using indirect
@@ -1186,7 +1163,6 @@ free_shadow:
 
         /* No more gnttab callback work. */
         gnttab_cancel_free_callback(&rinfo->callback);
-        spin_unlock_irq(&info->io_lock);
 
         /* Flush gnttab callback work. Must be done with no locks held. */
         flush_work(&rinfo->work);
@@ -1204,7 +1180,45 @@ free_shadow:
         if (rinfo->irq)
                 unbind_from_irqhandler(rinfo->irq, rinfo);
         rinfo->evtchn = rinfo->irq = 0;
+}
 
+static void blkif_free(struct blkfront_info *info, int suspend)
+{
+        struct grant *persistent_gnt, *n;
+        unsigned int i;
+
+        /* Prevent new requests being issued until we fix things up. */
+        spin_lock_irq(&info->io_lock);
+        info->connected = suspend ?
+                BLKIF_STATE_SUSPENDED : BLKIF_STATE_DISCONNECTED;
+        /* No more blkif_request(). */
+        if (info->rq)
+                blk_mq_stop_hw_queues(info->rq);
+
+        /* Remove all persistent grants */
+        if (!list_empty(&info->grants)) {
+                list_for_each_entry_safe(persistent_gnt, n,
+                                         &info->grants, node) {
+                        list_del(&persistent_gnt->node);
+                        if (persistent_gnt->gref != GRANT_INVALID_REF) {
+                                gnttab_end_foreign_access(persistent_gnt->gref,
+                                                          0, 0UL);
+                                info->persistent_gnts_c--;
+                        }
+                        if (info->feature_persistent)
+                                __free_page(persistent_gnt->page);
+                        kfree(persistent_gnt);
+                }
+        }
+        BUG_ON(info->persistent_gnts_c != 0);
+
+        for (i = 0; i < info->nr_rings; i++)
+                blkif_free_ring(&info->rinfo[i]);
+
+        kfree(info->rinfo);
+        info->rinfo = NULL;
+        info->nr_rings = 0;
+        spin_unlock_irq(&info->io_lock);
 }
 
 struct copy_from_grant {
@@ -1492,7 +1506,7 @@ static int talk_to_blkback(struct xenbus_device *dev,
         int err, i;
         unsigned int max_page_order = 0;
         unsigned int ring_page_order = 0;
-        struct blkfront_ring_info *rinfo = &info->rinfo;
+        struct blkfront_ring_info *rinfo;
 
         err = xenbus_scanf(XBT_NIL, info->xbdev->otherend,
                            "max-ring-page-order", "%u", &max_page_order);
@@ -1503,10 +1517,13 @@ static int talk_to_blkback(struct xenbus_device *dev,
                 info->nr_ring_pages = 1 << ring_page_order;
         }
 
-        /* Create shared ring, alloc event channel. */
-        err = setup_blkring(dev, rinfo);
-        if (err)
-                goto out;
+        for (i = 0; i < info->nr_rings; i++) {
+                rinfo = &info->rinfo[i];
+                /* Create shared ring, alloc event channel. */
+                err = setup_blkring(dev, rinfo);
+                if (err)
+                        goto destroy_blkring;
+        }
 
 again:
         err = xenbus_transaction_start(&xbt);
@@ -1515,37 +1532,43 @@ again:
                 goto destroy_blkring;
         }
 
-        if (info->nr_ring_pages == 1) {
-                err = xenbus_printf(xbt, dev->nodename,
-                                    "ring-ref", "%u", rinfo->ring_ref[0]);
-                if (err) {
-                        message = "writing ring-ref";
-                        goto abort_transaction;
-                }
-        } else {
-                err = xenbus_printf(xbt, dev->nodename,
-                                    "ring-page-order", "%u", ring_page_order);
-                if (err) {
-                        message = "writing ring-page-order";
-                        goto abort_transaction;
-                }
-
-                for (i = 0; i < info->nr_ring_pages; i++) {
-                        char ring_ref_name[RINGREF_NAME_LEN];
-
-                        snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
-                        err = xenbus_printf(xbt, dev->nodename, ring_ref_name,
-                                            "%u", rinfo->ring_ref[i]);
+        if (info->nr_rings == 1) {
+                rinfo = &info->rinfo[0];
+                if (info->nr_ring_pages == 1) {
+                        err = xenbus_printf(xbt, dev->nodename,
+                                            "ring-ref", "%u", rinfo->ring_ref[0]);
                         if (err) {
                                 message = "writing ring-ref";
                                 goto abort_transaction;
                         }
+                } else {
+                        err = xenbus_printf(xbt, dev->nodename,
+                                            "ring-page-order", "%u", ring_page_order);
+                        if (err) {
+                                message = "writing ring-page-order";
+                                goto abort_transaction;
+                        }
+
+                        for (i = 0; i < info->nr_ring_pages; i++) {
+                                char ring_ref_name[RINGREF_NAME_LEN];
+
+                                snprintf(ring_ref_name, RINGREF_NAME_LEN, "ring-ref%u", i);
+                                err = xenbus_printf(xbt, dev->nodename, ring_ref_name,
+                                                    "%u", rinfo->ring_ref[i]);
+                                if (err) {
+                                        message = "writing ring-ref";
+                                        goto abort_transaction;
+                                }
+                        }
                 }
-        }
-        err = xenbus_printf(xbt, dev->nodename,
-                            "event-channel", "%u", rinfo->evtchn);
-        if (err) {
-                message = "writing event-channel";
+                err = xenbus_printf(xbt, dev->nodename,
+                                    "event-channel", "%u", rinfo->evtchn);
+                if (err) {
+                        message = "writing event-channel";
+                        goto abort_transaction;
+                }
+        } else {
+                /* Not supported at this stage. */
                 goto abort_transaction;
         }
         err = xenbus_printf(xbt, dev->nodename, "protocol", "%s",
@@ -1568,9 +1591,15 @@ again:
                 goto destroy_blkring;
         }
 
-        for (i = 0; i < BLK_RING_SIZE(info); i++)
-                rinfo->shadow[i].req.u.rw.id = i+1;
-        rinfo->shadow[BLK_RING_SIZE(info)-1].req.u.rw.id = 0x0fffffff;
+        for (i = 0; i < info->nr_rings; i++) {
+                unsigned int j;
+
+                rinfo = &info->rinfo[i];
+
+                for (j = 0; j < BLK_RING_SIZE(info); j++)
+                        rinfo->shadow[j].req.u.rw.id = j + 1;
+                rinfo->shadow[BLK_RING_SIZE(info)-1].req.u.rw.id = 0x0fffffff;
+        }
         xenbus_switch_state(dev, XenbusStateInitialised);
 
         return 0;
@@ -1581,7 +1610,7 @@ again:
                 xenbus_dev_fatal(dev, err, "%s", message);
  destroy_blkring:
         blkif_free(info, 0);
- out:
+
         return err;
 }
 
@@ -1595,8 +1624,8 @@ static int blkfront_probe(struct xenbus_device *dev,
                           const struct xenbus_device_id *id)
 {
         int err, vdevice;
+        unsigned int r_index;
         struct blkfront_info *info;
-        struct blkfront_ring_info *rinfo;
 
         /* FIXME: Use dynamic device id if this is not set. */
         err = xenbus_scanf(XBT_NIL, dev->nodename,
@@ -1646,10 +1675,22 @@ static int blkfront_probe(struct xenbus_device *dev,
                 return -ENOMEM;
         }
 
-        rinfo = &info->rinfo;
-        INIT_LIST_HEAD(&rinfo->indirect_pages);
-        rinfo->dev_info = info;
-        INIT_WORK(&rinfo->work, blkif_restart_queue);
+        info->nr_rings = 1;
+        info->rinfo = kzalloc(sizeof(struct blkfront_ring_info) * info->nr_rings, GFP_KERNEL);
+        if (!info->rinfo) {
+                xenbus_dev_fatal(dev, -ENOMEM, "allocating ring_info structure");
+                kfree(info);
+                return -ENOMEM;
+        }
+
+        for (r_index = 0; r_index < info->nr_rings; r_index++) {
+                struct blkfront_ring_info *rinfo;
+
+                rinfo = &info->rinfo[r_index];
+                INIT_LIST_HEAD(&rinfo->indirect_pages);
+                rinfo->dev_info = info;
+                INIT_WORK(&rinfo->work, blkif_restart_queue);
+        }
 
         mutex_init(&info->mutex);
         spin_lock_init(&info->io_lock);
@@ -1681,7 +1722,7 @@ static void split_bio_end(struct bio *bio)
 
 static int blkif_recover(struct blkfront_info *info)
 {
-        int i;
+        unsigned int i, r_index;
         struct request *req, *n;
         struct blk_shadow *copy;
         int rc;
@@ -1691,57 +1732,62 @@ static int blkif_recover(struct blkfront_info *info)
         int pending, size;
         struct split_bio *split_bio;
         struct list_head requests;
-        struct blkfront_ring_info *rinfo = &info->rinfo;
-
-        /* Stage 1: Make a safe copy of the shadow state. */
-        copy = kmemdup(rinfo->shadow, sizeof(rinfo->shadow),
-                       GFP_NOIO | __GFP_REPEAT | __GFP_HIGH);
-        if (!copy)
-                return -ENOMEM;
-
-        /* Stage 2: Set up free list. */
-        memset(&rinfo->shadow, 0, sizeof(rinfo->shadow));
-        for (i = 0; i < BLK_RING_SIZE(info); i++)
-                rinfo->shadow[i].req.u.rw.id = i+1;
-        rinfo->shadow_free = rinfo->ring.req_prod_pvt;
-        rinfo->shadow[BLK_RING_SIZE(info)-1].req.u.rw.id = 0x0fffffff;
-
-        rc = blkfront_gather_backend_features(info);
-        if (rc) {
-                kfree(copy);
-                return rc;
-        }
 
+        blkfront_gather_backend_features(info);
         segs = info->max_indirect_segments ? : BLKIF_MAX_SEGMENTS_PER_REQUEST;
         blk_queue_max_segments(info->rq, segs);
         bio_list_init(&bio_list);
         INIT_LIST_HEAD(&requests);
-        for (i = 0; i < BLK_RING_SIZE(info); i++) {
-                /* Not in use? */
-                if (!copy[i].request)
-                        continue;
 
-                /*
-                 * Get the bios in the request so we can re-queue them.
-                 */
-                if (copy[i].request->cmd_flags &
-                    (REQ_FLUSH | REQ_FUA | REQ_DISCARD | REQ_SECURE)) {
+        for (r_index = 0; r_index < info->nr_rings; r_index++) {
+                struct blkfront_ring_info *rinfo;
+
+                rinfo = &info->rinfo[r_index];
+                /* Stage 1: Make a safe copy of the shadow state. */
+                copy = kmemdup(rinfo->shadow, sizeof(rinfo->shadow),
+                               GFP_NOIO | __GFP_REPEAT | __GFP_HIGH);
+                if (!copy)
+                        return -ENOMEM;
+
+                /* Stage 2: Set up free list. */
+                memset(&rinfo->shadow, 0, sizeof(rinfo->shadow));
+                for (i = 0; i < BLK_RING_SIZE(info); i++)
+                        rinfo->shadow[i].req.u.rw.id = i+1;
+                rinfo->shadow_free = rinfo->ring.req_prod_pvt;
+                rinfo->shadow[BLK_RING_SIZE(info)-1].req.u.rw.id = 0x0fffffff;
+
+                rc = blkfront_setup_indirect(rinfo);
+                if (rc) {
+                        kfree(copy);
+                        return rc;
+                }
+
+                for (i = 0; i < BLK_RING_SIZE(info); i++) {
+                        /* Not in use? */
+                        if (!copy[i].request)
+                                continue;
+
                         /*
-                         * Flush operations don't contain bios, so
-                         * we need to requeue the whole request
+                         * Get the bios in the request so we can re-queue them.
                          */
-                        list_add(&copy[i].request->queuelist, &requests);
-                        continue;
+                        if (copy[i].request->cmd_flags &
+                            (REQ_FLUSH | REQ_FUA | REQ_DISCARD | REQ_SECURE)) {
+                                /*
+                                 * Flush operations don't contain bios, so
+                                 * we need to requeue the whole request
+                                 */
+                                list_add(&copy[i].request->queuelist, &requests);
+                                continue;
+                        }
+                        merge_bio.head = copy[i].request->bio;
+                        merge_bio.tail = copy[i].request->biotail;
+                        bio_list_merge(&bio_list, &merge_bio);
+                        copy[i].request->bio = NULL;
+                        blk_end_request_all(copy[i].request, 0);
                 }
-                merge_bio.head = copy[i].request->bio;
-                merge_bio.tail = copy[i].request->biotail;
-                bio_list_merge(&bio_list, &merge_bio);
-                copy[i].request->bio = NULL;
-                blk_end_request_all(copy[i].request, 0);
-        }
-
-        kfree(copy);
 
+                kfree(copy);
+        }
         xenbus_switch_state(info->xbdev, XenbusStateConnected);
 
         spin_lock_irq(&info->io_lock);
@@ -1749,8 +1795,13 @@ static int blkif_recover(struct blkfront_info *info)
         /* Now safe for us to use the shared ring */
         info->connected = BLKIF_STATE_CONNECTED;
 
-        /* Kick any other new requests queued since we resumed */
-        kick_pending_request_queues(rinfo);
+        for (r_index = 0; r_index < info->nr_rings; r_index++) {
+                struct blkfront_ring_info *rinfo;
+
+                rinfo = &info->rinfo[r_index];
+                /* Kick any other new requests queued since we resumed */
+                kick_pending_request_queues(rinfo);
+        }
 
         list_for_each_entry_safe(req, n, &requests, queuelist) {
                 /* Requeue pending requests (flush or discard) */
@@ -1961,7 +2012,7 @@ out_of_memory:
 /*
  * Gather all backend feature-*
  */
-static int blkfront_gather_backend_features(struct blkfront_info *info)
+static void blkfront_gather_backend_features(struct blkfront_info *info)
 {
         int err;
         int barrier, flush, discard, persistent;
@@ -2016,8 +2067,6 @@ static int blkfront_gather_backend_features(struct blkfront_info *info)
         else
                 info->max_indirect_segments = min(indirect_segments,
                                                   xen_blkif_max_segments);
-
-        return blkfront_setup_indirect(&info->rinfo);
 }
 
 /*
@@ -2030,8 +2079,7 @@ static void blkfront_connect(struct blkfront_info *info)
         unsigned long sector_size;
         unsigned int physical_sector_size;
         unsigned int binfo;
-        int err;
-        struct blkfront_ring_info *rinfo = &info->rinfo;
+        int err, i;
 
         switch (info->connected) {
         case BLKIF_STATE_CONNECTED:
@@ -2088,11 +2136,15 @@ static void blkfront_connect(struct blkfront_info *info)
         if (err != 1)
                 physical_sector_size = sector_size;
 
-        err = blkfront_gather_backend_features(info);
-        if (err) {
-                xenbus_dev_fatal(info->xbdev, err, "setup_indirect at %s",
-                                 info->xbdev->otherend);
-                return;
+        blkfront_gather_backend_features(info);
+        for (i = 0; i < info->nr_rings; i++) {
+                err = blkfront_setup_indirect(&info->rinfo[i]);
+                if (err) {
+                        xenbus_dev_fatal(info->xbdev, err, "setup_indirect at %s",
+                                         info->xbdev->otherend);
+                        blkif_free(info, 0);
+                        break;
+                }
         }
 
         err = xlvbd_alloc_gendisk(sectors, info, binfo, sector_size,
@@ -2108,7 +2160,8 @@ static void blkfront_connect(struct blkfront_info *info)
         /* Kick pending requests. */
         spin_lock_irq(&info->io_lock);
         info->connected = BLKIF_STATE_CONNECTED;
-        kick_pending_request_queues(rinfo);
+        for (i = 0; i < info->nr_rings; i++)
+                kick_pending_request_queues(&info->rinfo[i]);
         spin_unlock_irq(&info->io_lock);
 
         add_disk(info->gd);