[RFC PATCH 1/1] block/ioctl: Add an ioctl to enable large folios for block buffered IO path

[Bharata B Rao]

In order to experiment using large folios for block devices read/write
operations, expose an ioctl that userspace can selectively use on the
raw block devices.

For the write path, this forces iomap layer to provision large
folios (via iomap_file_buffered_write()).

Signed-off-by: Bharata B Rao <bharata@xxxxxxx>
---
 block/ioctl.c           | 8 ++++++++
 include/uapi/linux/fs.h | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/block/ioctl.c b/block/ioctl.c
index 6554b728bae6..6af26a08ef34 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -548,6 +548,12 @@ static int blkdev_bszset(struct file *file, blk_mode_t mode,
 	return ret;
 }
 
+static int blkdev_set_large_folio(struct block_device *bdev)
+{
+	mapping_set_large_folios(bdev->bd_mapping);
+	return 0;
+}
+
 /*
  * Common commands that are handled the same way on native and compat
  * user space. Note the separate arg/argp parameters that are needed
@@ -632,6 +638,8 @@ static int blkdev_common_ioctl(struct block_device *bdev, blk_mode_t mode,
 		return blkdev_pr_preempt(bdev, mode, argp, true);
 	case IOC_PR_CLEAR:
 		return blkdev_pr_clear(bdev, mode, argp);
+	case BLKSETLFOLIO:
+		return blkdev_set_large_folio(bdev);
 	default:
 		return -ENOIOCTLCMD;
 	}
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index 753971770733..5c8a326b68a1 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -203,6 +203,8 @@ struct fsxattr {
 #define BLKROTATIONAL _IO(0x12,126)
 #define BLKZEROOUT _IO(0x12,127)
 #define BLKGETDISKSEQ _IOR(0x12,128,__u64)
+#define BLKSETLFOLIO _IO(0x12, 129)
+
 /*
  * A jump here: 130-136 are reserved for zoned block devices
  * (see uapi/linux/blkzoned.h)
-- 
2.34.1