rbd: simplify rbd_rq_fn()

In rbd_rq_fn(), requests are fetched from the block layer and each request is processed, looping through the request's list of bio's until they've all been consumed.

Separate the handling for a single request into its own function to make it a bit easier to see what's going on.

Signed-off-by Alex Elder <[email protected]>

---
  drivers/block/rbd.c |  119
+++++++++++++++++++++++++++------------------------
  1 file changed, 63 insertions(+), 56 deletions(-)

drivers/block/rbd.c +58 -0

index 8b79a5b..88b9b2e 100644
@@ -1583,6 +1583,64 @@ static struct rbd_req_coll *rbd_alloc_coll(int
 num_reqs)
  	return coll;
  }
 
+static int rbd_dev_do_request(struct request *rq,
+				struct rbd_device *rbd_dev,
+				struct ceph_snap_context *snapc,
+				u64 ofs, unsigned int size,
+				struct bio *bio_chain)
+{
+	int num_segs;
+	struct rbd_req_coll *coll;
+	unsigned int bio_offset;
+	int cur_seg = 0;
+
+	dout("%s 0x%x bytes at 0x%llx\n",
+		rq_data_dir(rq) == WRITE ? "write" : "read",
+		size, (unsigned long long) blk_rq_pos(rq) * SECTOR_SIZE);
+
+	num_segs = rbd_get_num_segments(&rbd_dev->header, ofs, size);
+	if (num_segs <= 0)
+		return num_segs;
+
+	coll = rbd_alloc_coll(num_segs);
+	if (!coll)
+		return -ENOMEM;
+
+	bio_offset = 0;
+	do {
+		u64 limit = rbd_segment_length(rbd_dev, ofs, size);
+		unsigned int clone_size;
+		struct bio *bio_clone;
+
+		BUG_ON(limit > (u64) UINT_MAX);
+		clone_size = (unsigned int) limit;
+		dout("bio_chain->bi_vcnt=%hu\n", bio_chain->bi_vcnt);
+
+		kref_get(&coll->kref);
+
+		/* Pass a cloned bio chain via an osd request */
+
+		bio_clone = bio_chain_clone_range(&bio_chain,
+					&bio_offset, clone_size,
+					GFP_ATOMIC);
+		if (bio_clone)
+			(void) rbd_do_op(rq, rbd_dev, snapc,
+					ofs, clone_size,
+					bio_clone, coll, cur_seg);
+		else
+			rbd_coll_end_req_index(rq, coll, cur_seg,
+						(s32) -ENOMEM,
+						clone_size);
+		size -= clone_size;
+		ofs += clone_size;
+
+		cur_seg++;
+	} while (size > 0);
+	kref_put(&coll->kref, rbd_coll_release);
+
+	return 0;
+}
+
  /*
   * block device queue callback

   */

drivers/block/rbd.c +1 -50

@@ -1596,10 +1654,8 @@ static void rbd_rq_fn(struct request_queue *q)
  		bool do_write;
  		unsigned int size;
  		u64 ofs;
-		int num_segs, cur_seg = 0;
-		struct rbd_req_coll *coll;
  		struct ceph_snap_context *snapc;
-		unsigned int bio_offset;
+		int result;
 
  		dout("fetched request\n");
 

@@ -1637,60 +1693,11 @@ static void rbd_rq_fn(struct request_queue *q)
  		ofs = blk_rq_pos(rq) * SECTOR_SIZE;
  		bio = rq->bio;
 
-		dout("%s 0x%x bytes at 0x%llx\n",
-		     do_write ? "write" : "read",
-		     size, (unsigned long long) blk_rq_pos(rq) * SECTOR_SIZE);
-
-		num_segs = rbd_get_num_segments(&rbd_dev->header, ofs, size);
-		if (num_segs <= 0) {
-			spin_lock_irq(q->queue_lock);
-			__blk_end_request_all(rq, num_segs);
-			ceph_put_snap_context(snapc);
-			continue;
-		}
-		coll = rbd_alloc_coll(num_segs);
-		if (!coll) {
-			spin_lock_irq(q->queue_lock);
-			__blk_end_request_all(rq, -ENOMEM);
-			ceph_put_snap_context(snapc);
-			continue;
-		}
-
-		bio_offset = 0;
-		do {
-			u64 limit = rbd_segment_length(rbd_dev, ofs, size);
-			unsigned int chain_size;
-			struct bio *bio_chain;
-
-			BUG_ON(limit > (u64) UINT_MAX);
-			chain_size = (unsigned int) limit;
-			dout("rq->bio->bi_vcnt=%hu\n", rq->bio->bi_vcnt);
-
-			kref_get(&coll->kref);
-
-			/* Pass a cloned bio chain via an osd request */
-
-			bio_chain = bio_chain_clone_range(&bio,
-						&bio_offset, chain_size,
-						GFP_ATOMIC);
-			if (bio_chain)
-				(void) rbd_do_op(rq, rbd_dev, snapc,
-						ofs, chain_size,
-						bio_chain, coll, cur_seg);
-			else
-				rbd_coll_end_req_index(rq, coll, cur_seg,
-						       (s32) -ENOMEM,
-						       chain_size);
-			size -= chain_size;
-			ofs += chain_size;
-

drivers/block/rbd.c +1 -0

+			__blk_end_request_all(rq, result);
  	}
  }
 

Quoted 9 lines · Alex Elder

In rbd_rq_fn(), requests are fetched from the block layer and each request is processed, looping through the request's list of bio's until they've all been consumed.

Separate the handling for a single request into its own function to make it a bit easier to see what's going on.

Signed-off-by Alex Elder <[email protected]>

---

Quoted 4 lines

(quoted diff) +1 -3

-
-        spin_lock_irq(q->queue_lock);
-
+        result = rbd_dev_do_request(rq, rbd_dev, snapc, ofs, size, bio);

Review

Quoted 3 lines

          ceph_put_snap_context(snapc);

(quoted diff) +2 -0

+        spin_lock_irq(q->queue_lock);
+        if (result < 0)

result may be 0 if num_segs == 0, which will make the request hang. I'm not sure if this will happen (or is even possible), but it's different from the previous behavior, which called __blk_end_request_all() in this case as well.

Quoted 4 lines

+            __blk_end_request_all(rq, result);
      }

}

In rbd_rq_fn(), requests are fetched from the block layer and each request is processed, looping through the request's list of bio's until they've all been consumed.

Separate the handling for a single request into its own function to make it a bit easier to see what's going on.

Signed-off-by Alex Elder <[email protected]>

---
v2: Changed to handle 0-length requests the same as before.

  drivers/block/rbd.c |  119
+++++++++++++++++++++++++++------------------------
  1 file changed, 63 insertions(+), 56 deletions(-)

drivers/block/rbd.c +58 -0

index 8d93b6a..738d1e4 100644
@@ -1583,6 +1583,64 @@ static struct rbd_req_coll *rbd_alloc_coll(int
 num_reqs)
  	return coll;
  }
 
+static int rbd_dev_do_request(struct request *rq,
+				struct rbd_device *rbd_dev,
+				struct ceph_snap_context *snapc,
+				u64 ofs, unsigned int size,
+				struct bio *bio_chain)
+{
+	int num_segs;
+	struct rbd_req_coll *coll;
+	unsigned int bio_offset;
+	int cur_seg = 0;
+
+	dout("%s 0x%x bytes at 0x%llx\n",
+		rq_data_dir(rq) == WRITE ? "write" : "read",
+		size, (unsigned long long) blk_rq_pos(rq) * SECTOR_SIZE);
+
+	num_segs = rbd_get_num_segments(&rbd_dev->header, ofs, size);
+	if (num_segs <= 0)
+		return num_segs;
+
+	coll = rbd_alloc_coll(num_segs);
+	if (!coll)
+		return -ENOMEM;
+
+	bio_offset = 0;
+	do {
+		u64 limit = rbd_segment_length(rbd_dev, ofs, size);
+		unsigned int clone_size;
+		struct bio *bio_clone;
+
+		BUG_ON(limit > (u64)UINT_MAX);
+		clone_size = (unsigned int)limit;
+		dout("bio_chain->bi_vcnt=%hu\n", bio_chain->bi_vcnt);
+
+		kref_get(&coll->kref);
+
+		/* Pass a cloned bio chain via an osd request */
+
+		bio_clone = bio_chain_clone_range(&bio_chain,
+					&bio_offset, clone_size,
+					GFP_ATOMIC);
+		if (bio_clone)
+			(void)rbd_do_op(rq, rbd_dev, snapc,
+					ofs, clone_size,
+					bio_clone, coll, cur_seg);
+		else
+			rbd_coll_end_req_index(rq, coll, cur_seg,
+						(s32)-ENOMEM,
+						clone_size);
+		size -= clone_size;
+		ofs += clone_size;
+
+		cur_seg++;
+	} while (size > 0);
+	kref_put(&coll->kref, rbd_coll_release);
+
+	return 0;
+}
+
  /*
   * block device queue callback

   */

drivers/block/rbd.c +5 -56

@@ -1596,10 +1654,8 @@ static void rbd_rq_fn(struct request_queue *q)
  		bool do_write;
  		unsigned int size;
  		u64 ofs;
-		int num_segs, cur_seg = 0;
-		struct rbd_req_coll *coll;
  		struct ceph_snap_context *snapc;
-		unsigned int bio_offset;
+		int result;
 
  		dout("fetched request\n");
 

@@ -1637,60 +1693,11 @@ static void rbd_rq_fn(struct request_queue *q)
  		ofs = blk_rq_pos(rq) * SECTOR_SIZE;
  		bio = rq->bio;
 
-		dout("%s 0x%x bytes at 0x%llx\n",
-		     do_write ? "write" : "read",
-		     size, (unsigned long long) blk_rq_pos(rq) * SECTOR_SIZE);
-
-		num_segs = rbd_get_num_segments(&rbd_dev->header, ofs, size);
-		if (num_segs <= 0) {
-			spin_lock_irq(q->queue_lock);
-			__blk_end_request_all(rq, num_segs);
-			ceph_put_snap_context(snapc);
-			continue;
-		}
-		coll = rbd_alloc_coll(num_segs);
-		if (!coll) {
-			spin_lock_irq(q->queue_lock);
-			__blk_end_request_all(rq, -ENOMEM);
-			ceph_put_snap_context(snapc);
-			continue;
-		}
-
-		bio_offset = 0;
-		do {
-			u64 limit = rbd_segment_length(rbd_dev, ofs, size);
-			unsigned int chain_size;
-			struct bio *bio_chain;
-
-			BUG_ON(limit > (u64) UINT_MAX);
-			chain_size = (unsigned int) limit;
-			dout("rq->bio->bi_vcnt=%hu\n", rq->bio->bi_vcnt);
-
-			kref_get(&coll->kref);
-
-			/* Pass a cloned bio chain via an osd request */
-
-			bio_chain = bio_chain_clone_range(&bio,
-						&bio_offset, chain_size,
-						GFP_ATOMIC);
-			if (bio_chain)
-				(void) rbd_do_op(rq, rbd_dev, snapc,
-						ofs, chain_size,
-						bio_chain, coll, cur_seg);
-			else
-				rbd_coll_end_req_index(rq, coll, cur_seg,
-						       (s32)-ENOMEM,
-						       chain_size);
-			size -= chain_size;
-			ofs += chain_size;
-
-			cur_seg++;
-		} while (size > 0);
-		kref_put(&coll->kref, rbd_coll_release);
-
-		spin_lock_irq(q->queue_lock);
-
+		result = rbd_dev_do_request(rq, rbd_dev, snapc, ofs, size, bio);
  		ceph_put_snap_context(snapc);
+		spin_lock_irq(q->queue_lock);
+		if (!size || result < 0)
+			__blk_end_request_all(rq, result);
  	}
  }
 

Now that a big hunk in the middle of rbd_rq_fn() has been moved into its own routine we can simplify it a little more.

Signed-off-by Alex Elder <[email protected]>

---

  drivers/block/rbd.c |   50
+++++++++++++++++++++++---------------------------
  1 file changed, 23 insertions(+), 27 deletions(-)

drivers/block/rbd.c +23 -27

index 88b9b2e..0a35c34 100644
@@ -1647,53 +1647,49 @@ static int rbd_dev_do_request(struct request *rq,
  static void rbd_rq_fn(struct request_queue *q)
  {
  	struct rbd_device *rbd_dev = q->queuedata;
+	bool read_only = rbd_dev->mapping.read_only;
  	struct request *rq;
 
  	while ((rq = blk_fetch_request(q))) {
-		struct bio *bio;
-		bool do_write;
-		unsigned int size;
-		u64 ofs;
-		struct ceph_snap_context *snapc;
+		struct ceph_snap_context *snapc = NULL;
  		int result;
 
  		dout("fetched request\n");
 
-		/* filter out block requests we don't understand */
+		/* Filter out block requests we don't understand */
+
  		if ((rq->cmd_type != REQ_TYPE_FS)) {
  			__blk_end_request_all(rq, 0);
  			continue;
  		}
+		spin_unlock_irq(q->queue_lock);
 
-		/* deduce our operation (read, write) */
-		do_write = (rq_data_dir(rq) == WRITE);
-		if (do_write && rbd_dev->mapping.read_only) {
-			__blk_end_request_all(rq, -EROFS);
-			continue;
-		}
+		/* Stop writes to a read-only device */
 
-		spin_unlock_irq(q->queue_lock);
+		result = -EROFS;
+		if (read_only && rq_data_dir(rq) == WRITE)
+			goto out_end_request;
+
+		/* Grab a reference to the snapshot context */
 
  		down_read(&rbd_dev->header_rwsem);
+		if (rbd_dev->exists) {
+			snapc = ceph_get_snap_context(rbd_dev->header.snapc);
+			rbd_assert(snapc != NULL);
+		}
+		up_read(&rbd_dev->header_rwsem);
 
-		if (!rbd_dev->exists) {
+		if (!snapc) {
  			rbd_assert(rbd_dev->spec->snap_id != CEPH_NOSNAP);
-			up_read(&rbd_dev->header_rwsem);
  			dout("request for non-existent snapshot");
-			spin_lock_irq(q->queue_lock);
-			__blk_end_request_all(rq, -ENXIO);
-			continue;
+			result = -ENXIO;
+			goto out_end_request;
  		}
 
-		snapc = ceph_get_snap_context(rbd_dev->header.snapc);
-
-		up_read(&rbd_dev->header_rwsem);
-
-		size = blk_rq_bytes(rq);
-		ofs = blk_rq_pos(rq) * SECTOR_SIZE;
-		bio = rq->bio;
-
-		result = rbd_dev_do_request(rq, rbd_dev, snapc, ofs, size, bio);
+		result = rbd_dev_do_request(rq, rbd_dev, snapc,
+				blk_rq_pos(rq) * SECTOR_SIZE,
+				blk_rq_bytes(rq), rq->bio);
+out_end_request:
  		ceph_put_snap_context(snapc);
  		spin_lock_irq(q->queue_lock);
  		if (result < 0)