Re: [PATCH v6 5/5] loop: Add support for provision requests

On Mon, May 15, 2023 at 5:37 AM Brian Foster [off-list ref] wrote:

On Fri, May 05, 2023 at 11:29:09PM -0700, Sarthak Kukreti wrote:

quoted

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.

Signed-off-by: Sarthak Kukreti <redacted>
---
 drivers/block/loop.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index bc31bb7072a2..13c4b4f8b9c1 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c

@@ -327,6 +327,24 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
      return ret;
 }

+static int lo_req_provision(struct loop_device *lo, struct request *rq, loff_t pos)
+{
+     struct file *file = lo->lo_backing_file;
+     struct request_queue *q = lo->lo_queue;
+     int ret;
+
+     if (!q->limits.max_provision_sectors) {
+             ret = -EOPNOTSUPP;
+             goto out;
+     }
+
+     ret = file->f_op->fallocate(file, 0, pos, blk_rq_bytes(rq));
+     if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
+             ret = -EIO;
+ out:
+     return ret;
+}
+
 static int lo_req_flush(struct loop_device *lo, struct request *rq)
 {
      int ret = vfs_fsync(lo->lo_backing_file, 0);

@@ -488,6 +506,8 @@ 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:
+             return lo_req_provision(lo, rq, pos);

Hi Sarthak,

The only thing that stands out to me is the separate lo_req_provision()
helper here. It seems it might be a little cleaner to extend and reuse
lo_req_fallocate()..? But that's not something I feel strongly about, so
this all looks pretty good to me either way, FWIW.

Fair point, I think that should shorten the patch (and for
correctness, we'd want to add FALLOC_FL_KEEP_SIZE for REQ_OP_PROVISION
too). I'll fix this up in v7.

Best
Sarthak

Brian

quoted

      case REQ_OP_WRITE:
              if (cmd->use_aio)
                      return lo_rw_aio(lo, cmd, pos, ITER_SOURCE);

@@ -754,6 +774,25 @@ 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 +1131,7 @@ static int loop_configure(struct loop_device *lo, fmode_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 +1344,7 @@ 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);

@@ -1830,6 +1871,7 @@ 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:
--

2.40.1.521.gf1e218fcd8-goog