linux-ext4 - [PATCH 1/3] ext4: fix overhead calculation to account for the reserved gdt blocks

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Message-Id: <20220415025440.2342107-1-tytso@mit.edu>
Date:   Thu, 14 Apr 2022 22:54:38 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     Fariya F <fariya.fatima03@...il.com>,
        "Theodore Ts'o" <tytso@....edu>, stable@...nel.org
Subject: [PATCH 1/3] ext4: fix overhead calculation to account for the reserved gdt blocks

The kernel calculation was underestimating the overhead by not taking
into account the reserved gdt blocks.  With this change, the overhead
calculated by the kernel matches the overhead calculation in mke2fs.

Signed-off-by: Theodore Ts'o <tytso@....edu>
Cc: stable@...nel.org
---
 fs/ext4/super.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index f2a5e78f93a9..23a9b2c086ed 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4177,9 +4177,11 @@ static int count_overhead(struct super_block *sb, ext4_group_t grp,
 	ext4_fsblk_t		first_block, last_block, b;
 	ext4_group_t		i, ngroups = ext4_get_groups_count(sb);
 	int			s, j, count = 0;
+	int			has_super = ext4_bg_has_super(sb, grp);
 
 	if (!ext4_has_feature_bigalloc(sb))
-		return (ext4_bg_has_super(sb, grp) + ext4_bg_num_gdb(sb, grp) +
+		return (has_super + ext4_bg_num_gdb(sb, grp) +
+			(has_super ? le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) : 0) +
 			sbi->s_itb_per_group + 2);
 
 	first_block = le32_to_cpu(sbi->s_es->s_first_data_block) +
-- 
2.31.0