Introduce new FALLOC_FL_ZERO_RANGE flag for fallocate. This has the same
functionality as xfs ioctl XFS_IOC_ZERO_RANGE.

We can also preallocate blocks past EOF in the same was as with
fallocate. Flag FALLOC_FL_KEEP_SIZE will cause the inode size to remain
the same even if we preallocate blocks past EOF.

It uses the same code to zero range as it is used by the
XFS_IOC_ZERO_RANGE ioctl.

Signed-off-by: Lukas Czerner <redacted>
---
 fs/xfs/xfs_file.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 64b48ea..aec5f64 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c

@@ -823,7 +823,8 @@ xfs_file_fallocate(
 
 	if (!S_ISREG(inode->i_mode))
 		return -EINVAL;
-	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
+	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE |
+		     FALLOC_FL_ZERO_RANGE))
 		return -EOPNOTSUPP;
 
 	xfs_ilock(ip, XFS_IOLOCK_EXCL);

@@ -840,8 +841,11 @@ xfs_file_fallocate(
 				goto out_unlock;
 		}
 
-		error = xfs_alloc_file_space(ip, offset, len,
-					     XFS_BMAPI_PREALLOC);
+		if (mode & FALLOC_FL_ZERO_RANGE)
+			error = xfs_zero_file_space(ip, offset, len);
+		else
+			error = xfs_alloc_file_space(ip, offset, len,
+						     XFS_BMAPI_PREALLOC);
 		if (error)
 			goto out_unlock;
 	}