[PATCH 5/5] fs/xfs: Allow toggle of physical DAX flag

ira.weiny
2019-10-20T16:00:07Z

From: Ira Weiny <ira.weiny@intel.com>

Switching between DAX and non-DAX on a file is racy with respect to data
operations. However, if no data is involved the flag is safe to switch.

Allow toggling the physical flag if a file is empty. The file length
check is not racy with respect to other operations as it is performed
under XFS_MMAPLOCK_EXCL and XFS_IOLOCK_EXCL locks.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
fs/xfs/xfs_ioctl.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index d3a7340d3209..3839684c249b 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -33,6 +33,7 @@
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_health.h"
+#include "libxfs/xfs_dir2.h"

#include <linux/mount.h>
#include <linux/namei.h>
@@ -1232,12 +1233,10 @@ xfs_diflags_to_linux(
inode->i_flags |= S_NOATIME;
else
inode->i_flags &= ~S_NOATIME;
-#if 0 /* disabled until the flag switching races are sorted out */
if (xflags & FS_XFLAG_DAX)
inode->i_flags |= S_DAX;
else
inode->i_flags &= ~S_DAX;
-#endif
}

static int
@@ -1320,6 +1319,12 @@ xfs_ioctl_setattr_dax_invalidate(

/* lock, flush and invalidate mapping in preparation for flag change */
xfs_ilock(ip, XFS_MMAPLOCK_EXCL | XFS_IOLOCK_EXCL);
+
+ if (i_size_read(inode) != 0) {
+ error = -EOPNOTSUPP;
+ goto out_unlock;
+ }
+
error = filemap_write_and_wait(inode->i_mapping);
if (error)
goto out_unlock;
--
2.20.1