Allocate a minimalist request_queue structure initially (needed for both
bio and request-based DM). A bio-based DM device no longer defaults to
having a fully initialized request_queue (request_fn, elevator, etc).
So bio-based DM devices no longer register elevator sysfs attributes
('iosched/' tree or 'scheduler' other than "none").

Initialization of a full request_queue (request_fn, elevator, etc) is
deferred until it is known that the DM device is request-based -- at the
end of the table load sequence.

Factor DM device's request_queue initialization:
- common to both request-based and bio-based into dm_init_md_queue().
- specific to request-based into dm_init_request_based_queue().

Adjust elv_iosched_show() to return "none" if !blk_queue_stackable.
This allows the block layer to take bio-based DM into consideration.

NOTE: It is still possible, albeit unlikely, for a bio-based device to
have a full request_queue. But in this case the unused elevator will
not be registered with sysfs. A table switch from request-based to
bio-based would be required, e.g.:

# dmsetup create --notable bio-based
# echo "0 100 multipath ..." | dmsetup load bio-based
# echo "0 100 linear ..." | dmsetup load bio-based
# dmsetup resume bio-based

Future work, in conjunction with userspace changes, could allow DM to
fix this by knowing which type of request_queue to initialize a priori
(instead of waiting until the end of the table load sequence).

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
---
block/elevator.c | 2 +-
drivers/md/dm-table.c | 6 +++
drivers/md/dm.c | 101 +++++++++++++++++++++++++++++++++++++------------
drivers/md/dm.h | 3 +
4 files changed, 86 insertions(+), 26 deletions(-)

diff --git a/block/elevator.c b/block/elevator.c
index 76e3702..e986e4c 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -1086,7 +1086,7 @@ ssize_t elv_iosched_show(struct request_queue *q, char *name)
struct elevator_type *__e;
int len = 0;

- if (!q->elevator)
+ if (!q->elevator || !blk_queue_stackable(q))
return sprintf(name, "none
");

elv = e->elevator_type;
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 9924ea2..dec8295 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -803,6 +803,7 @@ int dm_table_set_type(struct dm_table *t)
if (bio_based) {
/* We must use this table as bio-based */
t->type = DM_TYPE_BIO_BASED;
+ dm_clear_request_based_queue(t->md);
return 0;
}

@@ -829,6 +830,11 @@ int dm_table_set_type(struct dm_table *t)
return -EINVAL;
}

+ if (!dm_init_request_based_queue(t->md)) {
+ DMWARN("Cannot initialize queue for Request-based dm");
+ return -EINVAL;
+ }
+
t->type = DM_TYPE_REQUEST_BASED;

return 0;
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index d21e128..143082c 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1445,6 +1445,11 @@ static int dm_request_based(struct mapped_device *md)
return blk_queue_stackable(md->queue);
}

+static int dm_bio_based_md(struct mapped_device *md)
+{
+ return (md->queue->request_fn) ? 0 : 1;
+}
+
static int dm_request(struct request_queue *q, struct bio *bio)
{
struct mapped_device *md = q->queuedata;
@@ -1849,6 +1854,17 @@ static const struct block_device_operations dm_blk_dops;
static void dm_wq_work(struct work_struct *work);
static void dm_rq_barrier_work(struct work_struct *work);

+static void dm_init_md_queue(struct mapped_device *md)
+{
+ md->queue->queuedata = md;
+ md->queue->backing_dev_info.congested_fn = dm_any_congested;
+ md->queue->backing_dev_info.congested_data = md;
+ blk_queue_make_request(md->queue, dm_request);
+ blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
+ md->queue->unplug_fn = dm_unplug_all;
+ blk_queue_merge_bvec(md->queue, dm_merge_bvec);
+}
+
/*
* Allocate and initialise a blank device with a given minor.
*/
@@ -1886,34 +1902,11 @@ static struct mapped_device *alloc_dev(int minor)
INIT_LIST_HEAD(&md->uevent_list);
spin_lock_init(&md->uevent_lock);

- md->queue = blk_init_queue(dm_request_fn, NULL);
+ md->queue = blk_alloc_queue(GFP_KERNEL);
if (!md->queue)
goto bad_queue;

- /*
- * Request-based dm devices cannot be stacked on top of bio-based dm
- * devices. The type of this dm device has not been decided yet,
- * although we initialized the queue using blk_init_queue().
- * The type is decided at the first table loading time.
- * To prevent problematic device stacking, clear the queue flag
- * for request stacking support until then.
- *
- * This queue is new, so no concurrency on the queue_flags.
- */
- queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
- md->saved_make_request_fn = md->queue->make_request_fn;
- md->queue->queuedata = md;
- md->queue->backing_dev_info.congested_fn = dm_any_congested;
- md->queue->backing_dev_info.congested_data = md;
- blk_queue_make_request(md->queue, dm_request);
- blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
- md->queue->unplug_fn = dm_unplug_all;
- blk_queue_merge_bvec(md->queue, dm_merge_bvec);
- blk_queue_softirq_done(md->queue, dm_softirq_done);
- blk_queue_prep_rq(md->queue, dm_prep_fn);
- blk_queue_lld_busy(md->queue, dm_lld_busy);
- blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH,
- dm_rq_prepare_flush);
+ dm_init_md_queue(md);

md->disk = alloc_disk(1);
if (!md->disk)
@@ -1968,6 +1961,64 @@ bad_module_get:
return NULL;
}

+/*
+ * Fully initialize a request-based queue (->elevator, ->request_fn, etc).
+ */
+int dm_init_request_based_queue(struct mapped_device *md)
+{
+ struct request_queue *q = NULL;
+
+ /* Avoid re-initializing the queue if already fully initialized */
+ if (!md->queue->elevator) {
+ /* Fully initialize the queue */
+ q = blk_init_allocated_queue(md->queue, dm_request_fn, NULL);
+ if (!q)
+ return 0;
+ md->queue = q;
+ md->saved_make_request_fn = md->queue->make_request_fn;
+ dm_init_md_queue(md);
+ } else if (dm_bio_based_md(md)) {
+ /*
+ * Queue was fully initialized on behalf of a previous
+ * request-based table load. Table is now switching from
+ * bio-based back to request-based, e.g.: rq -> bio -> rq
+ */
+ md->queue->request_fn = dm_request_fn;
+ } else
+ return 1; /* already request-based */
+
+ elv_register_queue(md->queue);
+
+ /*
+ * Request-based dm devices cannot be stacked on top of bio-based dm
+ * devices. The type of this dm device has not been decided yet.
+ * The type is decided at the first table loading time.
+ * To prevent problematic device stacking, clear the queue flag
+ * for request stacking support until then.
+ *
+ * This queue is new, so no concurrency on the queue_flags.
+ */
+ queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
+
+ blk_queue_softirq_done(md->queue, dm_softirq_done);
+ blk_queue_prep_rq(md->queue, dm_prep_fn);
+ blk_queue_lld_busy(md->queue, dm_lld_busy);
+ blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH,
+ dm_rq_prepare_flush);
+
+ return 1;
+}
+
+void dm_clear_request_based_queue(struct mapped_device *md)
+{
+ if (dm_bio_based_md(md))
+ return; /* already bio-based */
+
+ /* Unregister elevator from sysfs and clear ->request_fn */
+ elv_unregister_queue(md->queue);
+ md->queue->request_fn = NULL;
+}
+
static void unlock_fs(struct mapped_device *md);

static void free_dev(struct mapped_device *md)
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index bad1724..95aec64 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -113,6 +113,9 @@ void dm_sysfs_exit(struct mapped_device *md);
struct kobject *dm_kobject(struct mapped_device *md);
struct mapped_device *dm_get_from_kobject(struct kobject *kobj);

+int dm_init_request_based_queue(struct mapped_device *md);
+void dm_clear_request_based_queue(struct mapped_device *md);
+
/*
* Targets for linear and striped mappings
*/

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