[PATCH 3.16 56/63] ext4: Introduce ext4_clamp_want_extra_isize()

[Ben Hutchings]

3.16.81-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben@xxxxxxxxxxxxxxx>

Based on commit 7bc04c5c2cc4 "ext4: fix use-after-free race with
debug_want_extra_isize".  We don't have that bug but this will make it
easier to backport commit 4ea99936a163 "ext4: add more paranoia
checking in ext4_expand_extra_isize handling".

Cc: Barret Rhoden <brho@xxxxxxxxxx>
Cc: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3423,6 +3423,36 @@ int ext4_calculate_overhead(struct super
 	return 0;
 }
 
+static void ext4_clamp_want_extra_isize(struct super_block *sb)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+
+	/* determine the minimum size of new large inodes, if present */
+	if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE) {
+		sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
+						     EXT4_GOOD_OLD_INODE_SIZE;
+		if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
+				       EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE)) {
+			if (sbi->s_want_extra_isize <
+			    le16_to_cpu(es->s_want_extra_isize))
+				sbi->s_want_extra_isize =
+					le16_to_cpu(es->s_want_extra_isize);
+			if (sbi->s_want_extra_isize <
+			    le16_to_cpu(es->s_min_extra_isize))
+				sbi->s_want_extra_isize =
+					le16_to_cpu(es->s_min_extra_isize);
+		}
+	}
+	/* Check if enough inode space is available */
+	if (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize >
+							sbi->s_inode_size) {
+		sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
+						       EXT4_GOOD_OLD_INODE_SIZE;
+		ext4_msg(sb, KERN_INFO,
+			 "required extra inode space not available");
+	}
+}
 
 static ext4_fsblk_t ext4_calculate_resv_clusters(struct super_block *sb)
 {
@@ -4245,30 +4275,7 @@ no_journal:
 	if (ext4_setup_super(sb, es, sb->s_flags & MS_RDONLY))
 		sb->s_flags |= MS_RDONLY;
 
-	/* determine the minimum size of new large inodes, if present */
-	if (sbi->s_inode_size > EXT4_GOOD_OLD_INODE_SIZE) {
-		sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
-						     EXT4_GOOD_OLD_INODE_SIZE;
-		if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
-				       EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE)) {
-			if (sbi->s_want_extra_isize <
-			    le16_to_cpu(es->s_want_extra_isize))
-				sbi->s_want_extra_isize =
-					le16_to_cpu(es->s_want_extra_isize);
-			if (sbi->s_want_extra_isize <
-			    le16_to_cpu(es->s_min_extra_isize))
-				sbi->s_want_extra_isize =
-					le16_to_cpu(es->s_min_extra_isize);
-		}
-	}
-	/* Check if enough inode space is available */
-	if (EXT4_GOOD_OLD_INODE_SIZE + sbi->s_want_extra_isize >
-							sbi->s_inode_size) {
-		sbi->s_want_extra_isize = sizeof(struct ext4_inode) -
-						       EXT4_GOOD_OLD_INODE_SIZE;
-		ext4_msg(sb, KERN_INFO, "required extra inode space not"
-			 "available");
-	}
+	ext4_clamp_want_extra_isize(sb);
 
 	err = ext4_reserve_clusters(sbi, ext4_calculate_resv_clusters(sb));
 	if (err) {