ext4: simplify i_state checks in __ext4_update_other_inode_time()

Since I_DIRTY_TIME and I_DIRTY_INODE are mutually exclusive in i_state,
there's no need to check for I_DIRTY_TIME && !I_DIRTY_INODE.  Just check
for I_DIRTY_TIME.

Also introduce a helper function in include/linux/fs.h to do this check.

Link: https://lore.kernel.org/r/20210112190253.64307-12-ebiggers@kernel.orgReviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/ext4/inode.c

@@ -4961,15 +4961,11 @@ static void __ext4_update_other_inode_time(struct super_block *sb,
 	if (!inode)
 		return;
 
-	if ((inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW |
-			       I_DIRTY_INODE)) ||
-	    ((inode->i_state & I_DIRTY_TIME) == 0))
+	if (!inode_is_dirtytime_only(inode))
 		return;
 
 	spin_lock(&inode->i_lock);
-	if (((inode->i_state & (I_FREEING | I_WILL_FREE | I_NEW |
-				I_DIRTY_INODE)) == 0) &&
-	    (inode->i_state & I_DIRTY_TIME)) {
+	if (inode_is_dirtytime_only(inode)) {
 		struct ext4_inode_info	*ei = EXT4_I(inode);
 
 		inode->i_state &= ~I_DIRTY_TIME;

include/linux/fs.h

@@ -2194,6 +2194,21 @@ static inline void mark_inode_dirty_sync(struct inode *inode)
 	__mark_inode_dirty(inode, I_DIRTY_SYNC);
 }
 
+/*
+ * Returns true if the given inode itself only has dirty timestamps (its pages
+ * may still be dirty) and isn't currently being allocated or freed.
+ * Filesystems should call this if when writing an inode when lazytime is
+ * enabled, they want to opportunistically write the timestamps of other inodes
+ * located very nearby on-disk, e.g. in the same inode block.  This returns true
+ * if the given inode is in need of such an opportunistic update.  Requires
+ * i_lock, or at least later re-checking under i_lock.
+ */
+static inline bool inode_is_dirtytime_only(struct inode *inode)
+{
+	return (inode->i_state & (I_DIRTY_TIME | I_NEW |
+				  I_FREEING | I_WILL_FREE)) == I_DIRTY_TIME;
+}
+
 extern void inc_nlink(struct inode *inode);
 extern void drop_nlink(struct inode *inode);
 extern void clear_nlink(struct inode *inode);