[PATCH V4 4/8] fs/ext4: Update ext4_should_use_dax()

[ira.weiny@xxxxxxxxx]

From: Ira Weiny <ira.weiny@xxxxxxxxx>

S_DAX should only be enabled when the underlying block device supports
dax.

Cache the underlying support for DAX in the super block and modify
ext4_should_use_dax() to check for device support prior to the over
riding mount option.

While we are at it change the function to ext4_should_enable_dax() as
this better reflects the ask as well as matches xfs.

Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>

---
Changes from V3:
	Add a sb DAX supported flag for performance

Changes from RFC
	Change function name to 'should enable'
	Clean up bool conversion
	Reorder this for better bisect-ability
---
 fs/ext4/ext4.h  |  1 +
 fs/ext4/inode.c | 15 ++++++++++-----
 fs/ext4/super.c |  5 ++++-
 3 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 1a3daf2d18ef..0b4db9ce7756 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1979,6 +1979,7 @@ static inline bool ext4_has_incompat_features(struct super_block *sb)
  */
 #define EXT4_FLAGS_RESIZING	0
 #define EXT4_FLAGS_SHUTDOWN	1
+#define EXT4_FLAGS_BDEV_IS_DAX	2
 
 static inline int ext4_forced_shutdown(struct ext4_sb_info *sbi)
 {
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index a10ff12194db..6532870f6a0b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4398,10 +4398,10 @@ int ext4_get_inode_loc(struct inode *inode, struct ext4_iloc *iloc)
 		!ext4_test_inode_state(inode, EXT4_STATE_XATTR));
 }
 
-static bool ext4_should_use_dax(struct inode *inode)
+static bool ext4_should_enable_dax(struct inode *inode)
 {
-	if (!test_opt(inode->i_sb, DAX_ALWAYS))
-		return false;
+	struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
+
 	if (!S_ISREG(inode->i_mode))
 		return false;
 	if (ext4_should_journal_data(inode))
@@ -4412,7 +4412,12 @@ static bool ext4_should_use_dax(struct inode *inode)
 		return false;
 	if (ext4_test_inode_flag(inode, EXT4_INODE_VERITY))
 		return false;
-	return true;
+	if (!test_bit(EXT4_FLAGS_BDEV_IS_DAX, &sbi->s_ext4_flags))
+		return false;
+	if (test_opt(inode->i_sb, DAX_ALWAYS))
+		return true;
+
+	return false;
 }
 
 void ext4_set_inode_flags(struct inode *inode)
@@ -4430,7 +4435,7 @@ void ext4_set_inode_flags(struct inode *inode)
 		new_fl |= S_NOATIME;
 	if (flags & EXT4_DIRSYNC_FL)
 		new_fl |= S_DIRSYNC;
-	if (ext4_should_use_dax(inode))
+	if (ext4_should_enable_dax(inode))
 		new_fl |= S_DAX;
 	if (flags & EXT4_ENCRYPT_FL)
 		new_fl |= S_ENCRYPTED;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7b99c44d0a91..f7d76dcaedfe 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4092,13 +4092,16 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		goto failed_mount;
 	}
 
+	if (bdev_dax_supported(sb->s_bdev, blocksize))
+		set_bit(EXT4_FLAGS_BDEV_IS_DAX, &sbi->s_ext4_flags);
+
 	if (sbi->s_mount_opt & EXT4_MOUNT_DAX_ALWAYS) {
 		if (ext4_has_feature_inline_data(sb)) {
 			ext4_msg(sb, KERN_ERR, "Cannot use DAX on a filesystem"
 					" that may contain inline data");
 			goto failed_mount;
 		}
-		if (!bdev_dax_supported(sb->s_bdev, blocksize)) {
+		if (!test_bit(EXT4_FLAGS_BDEV_IS_DAX, &sbi->s_ext4_flags)) {
 			ext4_msg(sb, KERN_ERR,
 				"DAX unsupported by block device.");
 			goto failed_mount;
-- 
2.25.1