[RFC PATCH v2 6/8] block: add FALLOC_FL_WRITE_ZEROES support

[Zhang Yi]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

Add support for FALLOC_FL_WRITE_ZEROES. It directly calls
blkdev_issue_zeroout() with flags set to 0. The underlying process will
attempt to use the fastest method for issuing zeroes. First, the block
layer will try to issue a write zeroes command if the storage device
supports it; if not, it will fall back to issuing zeroed data. Then, the
storage device driver may attempt to submit an unmap write zero command
if the device supports it; if not, the driver may fall back to
submitting a no-unmap write zeroes command.

Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 block/fops.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/block/fops.c b/block/fops.c
index 13a67940d040..56486de0960b 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -777,7 +777,7 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
 
 #define	BLKDEV_FALLOC_FL_SUPPORTED					\
 		(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |		\
-		 FALLOC_FL_ZERO_RANGE)
+		 FALLOC_FL_ZERO_RANGE | FALLOC_FL_WRITE_ZEROES)
 
 static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 			     loff_t len)
@@ -836,6 +836,15 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
 					     len >> SECTOR_SHIFT, GFP_KERNEL,
 					     BLKDEV_ZERO_NOFALLBACK);
 		break;
+	case FALLOC_FL_WRITE_ZEROES:
+		error = truncate_bdev_range(bdev, file_to_blk_mode(file), start, end);
+		if (error)
+			goto fail;
+
+		error = blkdev_issue_zeroout(bdev, start >> SECTOR_SHIFT,
+					     len >> SECTOR_SHIFT, GFP_KERNEL,
+					     0);
+		break;
 	default:
 		error = -EOPNOTSUPP;
 	}
-- 
2.39.2