[PATCH v2 4/4] fuse: support changing per-file DAX flag inside guest

[Jeffle Xu <jefflexu@linux.alibaba.com>]

Fuse client can enable or disable per-file DAX inside guest by
chattr(1). Similarly the new state won't be updated until the file is
closed and reopened later.

It is worth nothing that it is a best-effort style, since whether
per-file DAX is enabled or not is controlled by fuse_attr.flags retrieved
by FUSE LOOKUP routine, while the algorithm constructing fuse_attr.flags
is totally fuse server specific, not to mention ioctl may not be
supported by fuse server at all.

Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
---
 fs/fuse/ioctl.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/fuse/ioctl.c b/fs/fuse/ioctl.c
index 546ea3d58fb4..172e05c3f038 100644
--- a/fs/fuse/ioctl.c
+++ b/fs/fuse/ioctl.c
@@ -460,6 +460,7 @@ int fuse_fileattr_set(struct user_namespace *mnt_userns,
 	struct fuse_file *ff;
 	unsigned int flags = fa->flags;
 	struct fsxattr xfa;
+	bool newdax;
 	int err;
 
 	ff = fuse_priv_ioctl_prepare(inode);
@@ -467,10 +468,9 @@ int fuse_fileattr_set(struct user_namespace *mnt_userns,
 		return PTR_ERR(ff);
 
 	if (fa->flags_valid) {
+		newdax = flags & FS_DAX_FL;
 		err = fuse_priv_ioctl(inode, ff, FS_IOC_SETFLAGS,
 				      &flags, sizeof(flags));
-		if (err)
-			goto cleanup;
 	} else {
 		memset(&xfa, 0, sizeof(xfa));
 		xfa.fsx_xflags = fa->fsx_xflags;
@@ -479,11 +479,14 @@ int fuse_fileattr_set(struct user_namespace *mnt_userns,
 		xfa.fsx_projid = fa->fsx_projid;
 		xfa.fsx_cowextsize = fa->fsx_cowextsize;
 
+		newdax = fa->fsx_xflags & FS_XFLAG_DAX;
 		err = fuse_priv_ioctl(inode, ff, FS_IOC_FSSETXATTR,
 				      &xfa, sizeof(xfa));
 	}
 
-cleanup:
+	if (!err && IS_ENABLED(CONFIG_FUSE_DAX))
+		fuse_dax_dontcache(inode, newdax);
+
 	fuse_priv_ioctl_cleanup(inode, ff);
 
 	return err;
-- 
2.27.0