[PATCH v4 02/12] dax: introduce IS_DEVDAX() and IS_FSDAX()

[Dan Williams <dan.j.williams@intel.com>]

The current IS_DAX() helper that checks the S_DAX inode flag is
ambiguous, and currently has the broken assumption that the S_DAX flag
is only non-zero in the CONFIG_FS_DAX=y case. In preparation for
defining S_DAX to non-zero in the  CONFIG_FS_DAX=n + CONFIG_DEV_DAX=y
case, introduce two explicit helpers to replace IS_DAX().

Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-xfs@vger.kernel.org (supporter:XFS FILESYSTEM)
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: <stable@vger.kernel.org>
Fixes: dee410792419 ("/dev/dax, core: file operations and dax-mmap")
Reported-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/fs.h |   22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 79c413985305..bd0c46880572 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1909,6 +1909,28 @@ static inline bool sb_rdonly(const struct super_block *sb) { return sb->s_flags
 #define IS_WHITEOUT(inode)	(S_ISCHR(inode->i_mode) && \
 				 (inode)->i_rdev == WHITEOUT_DEV)
 
+static inline bool IS_DEVDAX(struct inode *inode)
+{
+	if (!IS_ENABLED(CONFIG_DEV_DAX))
+		return false;
+	if ((inode->i_flags & S_DAX) == 0)
+		return false;
+	if (!S_ISCHR(inode->i_mode))
+		return false;
+	return true;
+}
+
+static inline bool IS_FSDAX(struct inode *inode)
+{
+	if (!IS_ENABLED(CONFIG_FS_DAX))
+		return false;
+	if ((inode->i_flags & S_DAX) == 0)
+		return false;
+	if (S_ISCHR(inode->i_mode))
+		return false;
+	return true;
+}
+
 static inline bool HAS_UNMAPPED_ID(struct inode *inode)
 {
 	return !uid_valid(inode->i_uid) || !gid_valid(inode->i_gid);