The existing hash algorithms each come in signed and unsigned variants,
with the latter indicated by EXT2_FLAGS_UNSIGNED_HASH. Internally, ext4
represents those by adding a delta to the hash algorithm identifier that
takes them out of the range permitted on disk.
In the ext4_sb_info, s_def_hash_version is the value that actually
appears on disk, and s_hash_unsigned is the extra delta that is
inferred from the flags.
It used to be simply the magic value 3, but give it a symbolic name so
it can be changed freely if more on-disk values are added.
Signed-off-by: George Spelvin <linux@xxxxxxxxxxx>
---
This is my draft with clarified comments. Any better?
fs/ext4/ext4.h | 16 ++++++++++++----
fs/ext4/super.c | 7 ++++---
2 files changed, 16 insertions(+), 7 deletions(-)
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 1bbe7c31..07b13c7c 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1216,7 +1216,7 @@ struct ext4_sb_info {
u32 s_next_generation;
u32 s_hash_seed[4];
int s_def_hash_version;
- int s_hash_unsigned; /* 3 if hash should be signed, 0 if not */
+ int s_hash_unsigned; /* DX_HASH_UNSIGNED_DELTA, or 0 if signed */
struct percpu_counter s_freeclusters_counter;
struct percpu_counter s_freeinodes_counter;
struct percpu_counter s_dirs_counter;
@@ -1737,9 +1737,17 @@ static inline __le16 ext4_rec_len_to_disk(unsigned len, unsigned blocksize)
#define DX_HASH_LEGACY 0
#define DX_HASH_HALF_MD4 1
#define DX_HASH_TEA 2
-#define DX_HASH_LEGACY_UNSIGNED 3
-#define DX_HASH_HALF_MD4_UNSIGNED 4
-#define DX_HASH_TEA_UNSIGNED 5
+
+#define DX_HASH_UNSIGNED_DELTA 3 /* One more than ever appears on disk! */
+
+/*
+ * For historical reasons, the first three hash algorithms
+ * have signed and unsigned variants. The following values
+ * never appear on disk, but are used by the software.
+ */
+#define DX_HASH_LEGACY_UNSIGNED (DX_HASH_LEGACY + DX_HASH_UNSIGNED_DELTA)
+#define DX_HASH_HALF_MD4_UNSIGNED (DX_HASH_HALF_MD4 + DX_HASH_UNSIGNED_DELTA)
+#define DX_HASH_TEA_UNSIGNED (DX_HASH_TEA + DX_HASH_UNSIGNED_DELTA)
static inline u32 ext4_chksum(struct ext4_sb_info *sbi, u32 crc,
const void *address, unsigned int length)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 4566c2fe..6eb2c47a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3721,16 +3721,17 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
for (i = 0; i < 4; i++)
sbi->s_hash_seed[i] = le32_to_cpu(es->s_hash_seed[i]);
sbi->s_def_hash_version = es->s_def_hash_version;
- if (EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_DIR_INDEX)) {
+ if (sbi->s_def_hash_version <= DX_HASH_TEA &&
+ EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_DIR_INDEX)) {
i = le32_to_cpu(es->s_flags);
if (i & EXT2_FLAGS_UNSIGNED_HASH)
- sbi->s_hash_unsigned = 3;
+ sbi->s_hash_unsigned = DX_HASH_UNSIGNED_DELTA;
else if ((i & EXT2_FLAGS_SIGNED_HASH) == 0) {
#ifdef __CHAR_UNSIGNED__
if (!(sb->s_flags & MS_RDONLY))
es->s_flags |=
cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH);
- sbi->s_hash_unsigned = 3;
+ sbi->s_hash_unsigned = DX_HASH_UNSIGNED_DELTA;
#else
if (!(sb->s_flags & MS_RDONLY))
es->s_flags |=
--
2.1.0
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