[PATCH v2] loop: change queue block size to match when using DIO.

[Martijn Coenen]

The loop driver assumes that if the passed in fd is opened with
O_DIRECT, the caller wants to use direct I/O on the loop device.
However, if the underlying block device has a different block size than
the loop block queue, direct I/O can't be enabled. Instead of requiring
userspace to manually change the blocksize and re-enable direct I/O,
just change the queue block sizes to match, as well as the io_min size.

Signed-off-by: Martijn Coenen <maco@xxxxxxxxxxx>
---
v2 changes:
- Fixed commit message to say the block size must match the underlying
  block device, not the underlying filesystem.
- Also set physical blocksize and minimal io size correspondingly.

 drivers/block/loop.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index ab7ca5989097a..b547182037af2 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -994,6 +994,16 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
 	if (!(lo_flags & LO_FLAGS_READ_ONLY) && file->f_op->fsync)
 		blk_queue_write_cache(lo->lo_queue, true, false);
 
+	if (io_is_direct(lo->lo_backing_file) && inode->i_sb->s_bdev) {
+		/* In case of direct I/O, match underlying block size */
+		unsigned short bsize = bdev_logical_block_size(
+			inode->i_sb->s_bdev);
+
+		blk_queue_logical_block_size(lo->lo_queue, bsize);
+		blk_queue_physical_block_size(lo->lo_queue, bsize);
+		blk_queue_io_min(lo->lo_queue, bsize);
+	}
+
 	loop_update_rotational(lo);
 	loop_update_dio(lo);
 	set_capacity(lo->lo_disk, size);
-- 
2.23.0.187.g17f5b7556c-goog