[PATCH v9 3/3] loop: Add support for provision requests

[Sarthak Kukreti <sarthakkukreti@chromium.org>]

Add support for provision requests to loopback devices. Loop devices
will configure provision support based on whether the underlying block
device/file can support the provision request and, upon receiving a
provision bio, will map it to the backing device/storage. For loop devices
over files, a REQ_OP_PROVISION request will translate to an fallocate()
mode 0 call on the backing file.

Caveat: For filesystems with copy-on-write semantics, REQ_OP_PROVISION
will guarantee the success of only the next write to the provisioned range
with a ENOSPC.

Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
 drivers/block/loop.c | 39 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 9f2d412fc560..c84d4acdb18c 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -311,16 +311,20 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
 {
 	/*
 	 * We use fallocate to manipulate the space mappings used by the image
-	 * a.k.a. discard/zerorange.
+	 * a.k.a. discard/provision/zerorange.
 	 */
 	struct file *file = lo->lo_backing_file;
 	int ret;
 
-	mode |= FALLOC_FL_KEEP_SIZE;
+	if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE) &&
+	    !bdev_max_discard_sectors(lo->lo_device))
+		return -EOPNOTSUPP;
 
-	if (!bdev_max_discard_sectors(lo->lo_device))
+	if (mode == 0 && !bdev_max_provision_sectors(lo->lo_device))
 		return -EOPNOTSUPP;
 
+	mode |= FALLOC_FL_KEEP_SIZE;
+
 	ret = file->f_op->fallocate(file, mode, pos, blk_rq_bytes(rq));
 	if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
 		return -EIO;
@@ -488,6 +492,13 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
 				FALLOC_FL_PUNCH_HOLE);
 	case REQ_OP_DISCARD:
 		return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE);
+	case REQ_OP_PROVISION:
+		/*
+		 * fallocate() guarantees that the next writes to the
+		 * provisioned range will succeed without ENOSPC but does not
+		 * guarantee that every write to this range will succeed.
+		 */
+		return lo_fallocate(lo, rq, pos, 0);
 	case REQ_OP_WRITE:
 		if (cmd->use_aio)
 			return lo_rw_aio(lo, cmd, pos, ITER_SOURCE);
@@ -754,6 +765,25 @@ static void loop_sysfs_exit(struct loop_device *lo)
 				   &loop_attribute_group);
 }
 
+static void loop_config_provision(struct loop_device *lo)
+{
+	struct file *file = lo->lo_backing_file;
+	struct inode *inode = file->f_mapping->host;
+
+	/*
+	 * If the backing device is a block device, mirror its provisioning
+	 * capability.
+	 */
+	if (S_ISBLK(inode->i_mode)) {
+		blk_queue_max_provision_sectors(lo->lo_queue,
+			bdev_max_provision_sectors(I_BDEV(inode)));
+	} else if (file->f_op->fallocate) {
+		blk_queue_max_provision_sectors(lo->lo_queue, UINT_MAX >> 9);
+	} else {
+		blk_queue_max_provision_sectors(lo->lo_queue, 0);
+	}
+}
+
 static void loop_config_discard(struct loop_device *lo)
 {
 	struct file *file = lo->lo_backing_file;
@@ -1092,6 +1122,7 @@ static int loop_configure(struct loop_device *lo, blk_mode_t mode,
 	blk_queue_io_min(lo->lo_queue, bsize);
 
 	loop_config_discard(lo);
+	loop_config_provision(lo);
 	loop_update_rotational(lo);
 	loop_update_dio(lo);
 	loop_sysfs_init(lo);
@@ -1304,6 +1335,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
 	}
 
 	loop_config_discard(lo);
+	loop_config_provision(lo);
 
 	/* update dio if lo_offset or transfer is changed */
 	__loop_update_dio(lo, lo->use_dio);
@@ -1857,6 +1889,7 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
 	case REQ_OP_FLUSH:
 	case REQ_OP_DISCARD:
 	case REQ_OP_WRITE_ZEROES:
+	case REQ_OP_PROVISION:
 		cmd->use_aio = false;
 		break;
 	default:
-- 
2.39.2