[PATCH v5 8/8] block: implement write zero pages cmd

[Pavel Begunkov <asml.silence@gmail.com>]

Add a command that writes the zero page to the drive. Apart from passing
the zero page instead of actual data it uses the normal write path and
doesn't do any further acceleration. Subsequently, it doesn't requires
any special hardware support, and for example can be used as a fallback
option for BLOCK_URING_CMD_WRITE_ZEROES.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 block/ioctl.c               | 21 ++++++++++++++++++---
 include/uapi/linux/blkdev.h |  1 +
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/block/ioctl.c b/block/ioctl.c
index f8f6d6a71ff0..08e0d2d52b06 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -780,7 +780,8 @@ static void bio_cmd_bio_end_io(struct bio *bio)
 
 static int blkdev_cmd_write_zeroes(struct io_uring_cmd *cmd,
 				   struct block_device *bdev,
-				   uint64_t start, uint64_t len, bool nowait)
+				   uint64_t start, uint64_t len,
+				   bool nowait, bool zero_pages)
 {
 	struct blk_iou_cmd *bic = io_uring_cmd_to_pdu(cmd, struct blk_iou_cmd);
 	sector_t bs_mask = (bdev_logical_block_size(bdev) >> SECTOR_SHIFT) - 1;
@@ -799,6 +800,17 @@ static int blkdev_cmd_write_zeroes(struct io_uring_cmd *cmd,
 	if (err)
 		return err;
 
+	if (zero_pages) {
+		err = blkdev_issue_zero_pages_bio(bdev, sector, nr_sects,
+						  gfp, &prev,
+						  BLKDEV_ZERO_PAGES_NOWAIT);
+		if (!prev)
+			return -EAGAIN;
+		if (err)
+			bic->res = err;
+		goto out_submit;
+	}
+
 	if (!limit)
 		return -EOPNOTSUPP;
 	/*
@@ -834,7 +846,7 @@ static int blkdev_cmd_write_zeroes(struct io_uring_cmd *cmd,
 		return -EAGAIN;
 	if (unlikely(nr_sects))
 		bic->res = -EAGAIN;
-
+out_submit:
 	prev->bi_private = cmd;
 	prev->bi_end_io = bio_cmd_bio_end_io;
 	submit_bio(prev);
@@ -921,7 +933,10 @@ int blkdev_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags)
 		return blkdev_cmd_discard(cmd, bdev, start, len, bic->nowait);
 	case BLOCK_URING_CMD_WRITE_ZEROES:
 		return blkdev_cmd_write_zeroes(cmd, bdev, start, len,
-					       bic->nowait);
+					       bic->nowait, false);
+	case BLOCK_URING_CMD_WRITE_ZERO_PAGE:
+		return blkdev_cmd_write_zeroes(cmd, bdev, start, len,
+					       bic->nowait, true);
 	}
 	return -EINVAL;
 }
diff --git a/include/uapi/linux/blkdev.h b/include/uapi/linux/blkdev.h
index b4664139a82a..880b292d2d0d 100644
--- a/include/uapi/linux/blkdev.h
+++ b/include/uapi/linux/blkdev.h
@@ -11,5 +11,6 @@
  */
 #define BLOCK_URING_CMD_DISCARD			_IO(0x12, 0)
 #define BLOCK_URING_CMD_WRITE_ZEROES		_IO(0x12, 1)
+#define BLOCK_URING_CMD_WRITE_ZERO_PAGE		_IO(0x12, 2)
 
 #endif
-- 
2.45.2