[PATCH 2/2] mkfs: allow setting dax flag on root directory

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

Teach mkfs to set the DAX flag on the root directory so that all new
files can be created in dax mode.  This is a complement to removing the
mount option.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 man/man8/mkfs.xfs.8 |   11 +++++++++++
 mkfs/xfs_mkfs.c     |   14 ++++++++++++++
 2 files changed, 25 insertions(+)


diff --git a/man/man8/mkfs.xfs.8 b/man/man8/mkfs.xfs.8
index 9d762a43011a..4b4fdd86b2f4 100644
--- a/man/man8/mkfs.xfs.8
+++ b/man/man8/mkfs.xfs.8
@@ -394,6 +394,17 @@ All inodes created by
 will have this extent size hint applied.
 The value must be provided in units of filesystem blocks.
 Directories will pass on this hint to newly created children.
+.TP
+.BI dax= value
+All inodes created by
+.B mkfs.xfs
+will have the DAX flag set.
+This means that directories will pass the flag on to newly created files
+and files will use the DAX IO paths when possible.
+This value is either 1 to enable the use or 0 to disable.
+By default,
+.B mkfs.xfs
+will not enable DAX mode.
 .RE
 .TP
 .B \-f
diff --git a/mkfs/xfs_mkfs.c b/mkfs/xfs_mkfs.c
index 2e6cd280e388..33507f6ea21c 100644
--- a/mkfs/xfs_mkfs.c
+++ b/mkfs/xfs_mkfs.c
@@ -60,6 +60,7 @@ enum {
 	D_PROJINHERIT,
 	D_EXTSZINHERIT,
 	D_COWEXTSIZE,
+	D_DAX,
 	D_MAX_OPTS,
 };
 
@@ -254,6 +255,7 @@ static struct opt_params dopts = {
 		[D_PROJINHERIT] = "projinherit",
 		[D_EXTSZINHERIT] = "extszinherit",
 		[D_COWEXTSIZE] = "cowextsize",
+		[D_DAX] = "dax",
 	},
 	.subopt_params = {
 		{ .index = D_AGCOUNT,
@@ -369,6 +371,12 @@ static struct opt_params dopts = {
 		  .maxval = UINT_MAX,
 		  .defaultval = SUBOPT_NEEDS_VAL,
 		},
+		{ .index = D_DAX,
+		  .conflicts = { { NULL, LAST_CONFLICT } },
+		  .minval = 0,
+		  .maxval = 1,
+		  .defaultval = 1,
+		},
 	},
 };
 
@@ -1434,6 +1442,12 @@ data_opts_parser(
 		cli->fsx.fsx_cowextsize = getnum(value, opts, subopt);
 		cli->fsx.fsx_xflags |= FS_XFLAG_COWEXTSIZE;
 		break;
+	case D_DAX:
+		if (getnum(value, opts, subopt))
+			cli->fsx.fsx_xflags |= FS_XFLAG_DAX;
+		else
+			cli->fsx.fsx_xflags &= ~FS_XFLAG_DAX;
+		break;
 	default:
 		return -EINVAL;
 	}