[PATCH,RFC] ext4: Add support for non-native signed/unsigned htree hash algorithms

Theodore Ts'o
2008-10-21T05:19:24Z

The original ext3 hash algorithms assumed that variables of type char
were signed, as God and K&R intended. Unfortunately, this assumption
is not true on some architectures. Userspace support for marking
filesystems with non-native signed/unsigned chars was added two years
ago, but the kernel-side support was never added (until now).

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
---
fs/ext4/ext4.h | 3 +++
fs/ext4/ext4_sb.h | 1 +
fs/ext4/hash.c | 42 +++++++++++++++++++++++++++++++++---------
fs/ext4/namei.c | 7 +++++++
fs/ext4/super.c | 15 +++++++++++++++
5 files changed, 59 insertions(+), 9 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 4880cc3..22cb2a4 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -891,6 +891,9 @@ static inline __le16 ext4_rec_len_to_disk(unsigned len)
#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

#ifdef __KERNEL__

diff --git a/fs/ext4/ext4_sb.h b/fs/ext4/ext4_sb.h
index 445fde6..2f3b8b1 100644
--- a/fs/ext4/ext4_sb.h
+++ b/fs/ext4/ext4_sb.h
@@ -57,6 +57,7 @@ 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 */
struct percpu_counter s_freeblocks_counter;
struct percpu_counter s_freeinodes_counter;
struct percpu_counter s_dirs_counter;
diff --git a/fs/ext4/hash.c b/fs/ext4/hash.c
index 556ca8e..d8fd725 100644
--- a/fs/ext4/hash.c
+++ b/fs/ext4/hash.c
@@ -35,11 +35,20 @@ static void TEA_transform(__u32 buf[4], __u32 const in[])

/* The old legacy hash */
-static __u32 dx_hack_hash(const char *name, int len)
+static __u32 dx_hack_hash(const char *name, int len, int unsigned_flag)
{
- __u32 hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
+ __u32 hash, hash0 = 0x12a3fe2d, hash1 = 0x37abe8f9;
+ const unsigned char *ucp = (const unsigned char *) name;
+ const signed char *scp = (const signed char *) name;
+ int c;
+
while (len--) {
- __u32 hash = hash1 + (hash0 ^ (*name++ * 7152373));
+ if (unsigned_flag)
+ c = (int) *ucp++;
+ else
+ c = (int) *scp++;
+
+ hash = hash1 + (hash0 ^ (c * 7152373));

if (hash & 0x80000000) hash -= 0x7fffffff;
hash1 = hash0;
@@ -48,10 +57,13 @@ static __u32 dx_hack_hash(const char *name, int len)
return (hash0 << 1);
}

-static void str2hashbuf(const char *msg, int len, __u32 *buf, int num)
+static void str2hashbuf(const char *msg, int len, __u32 *buf, int num,
+ int unsigned_flag)
{
__u32 pad, val;
- int i;
+ int i, c;
+ const unsigned char *ucp = (const unsigned char *) msg;
+ const signed char *scp = (const signed char *) msg;

pad = (__u32)len | ((__u32)len << 8);
pad |= pad << 16;
@@ -62,7 +74,12 @@ static void str2hashbuf(const char *msg, int len, __u32 *buf, int num)
for (i = 0; i < len; i++) {
if ((i % 4) == 0)
val = pad;
- val = msg[i] + (val << 8);
+ if (unsigned_flag)
+ c = (int) ucp[i];
+ else
+ c = (int) scp[i];
+
+ val = c + (val << 8);
if ((i % 4) == 3) {
*buf++ = val;
val = pad;
@@ -95,6 +112,7 @@ int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
const char *p;
int i;
__u32 in[8], buf[4];
+ int unsigned_flag = 0;

/* Initialize the default seed for the hash checksum functions */
buf[0] = 0x67452301;
@@ -113,13 +131,17 @@ int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
}

switch (hinfo->hash_version) {
+ case DX_HASH_LEGACY_UNSIGNED:
+ unsigned_flag++;
case DX_HASH_LEGACY:
- hash = dx_hack_hash(name, len);
+ hash = dx_hack_hash(name, len, unsigned_flag);
break;
+ case DX_HASH_HALF_MD4_UNSIGNED:
+ unsigned_flag++;
case DX_HASH_HALF_MD4:
p = name;
while (len > 0) {
- str2hashbuf(p, len, in, 8);
+ str2hashbuf(p, len, in, 8, unsigned_flag);
half_md4_transform(buf, in);
len -= 32;
p += 32;
@@ -127,10 +149,12 @@ int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
minor_hash = buf[2];
hash = buf[1];
break;
+ case DX_HASH_TEA_UNSIGNED:
+ unsigned_flag++;
case DX_HASH_TEA:
p = name;
while (len > 0) {
- str2hashbuf(p, len, in, 4);
+ str2hashbuf(p, len, in, 4, unsigned_flag);
TEA_transform(buf, in);
len -= 16;
p += 16;
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 92db9e9..80f59bf 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -372,6 +372,8 @@ dx_probe(const struct qstr *d_name, struct inode *dir,
goto fail;
}
hinfo->hash_version = root->info.hash_version;
+ if (hinfo->hash_version <= DX_HASH_TEA)
+ hinfo->hash_version += EXT4_SB(dir->i_sb)->s_hash_unsigned;
hinfo->seed = EXT4_SB(dir->i_sb)->s_hash_seed;
if (d_name)
ext4fs_dirhash(d_name->name, d_name->len, hinfo);
@@ -641,6 +643,9 @@ int ext4_htree_fill_tree(struct file *dir_file, __u32 start_hash,
dir = dir_file->f_path.dentry->d_inode;
if (!(EXT4_I(dir)->i_flags & EXT4_INDEX_FL)) {
hinfo.hash_version = EXT4_SB(dir->i_sb)->s_def_hash_version;
+ if (hinfo.hash_version <= DX_HASH_TEA)
+ hinfo.hash_version +=
+ EXT4_SB(dir->i_sb)->s_hash_unsigned;
hinfo.seed = EXT4_SB(dir->i_sb)->s_hash_seed;
count = htree_dirblock_to_tree(dir_file, dir, 0, &hinfo,
start_hash, start_minor_hash);
@@ -1418,6 +1423,8 @@ static int make_indexed_dir(handle_t *handle, struct dentry *dentry,

/* Initialize as for dx_probe */
hinfo.hash_version = root->info.hash_version;
+ if (hinfo.hash_version <= DX_HASH_TEA)
+ hinfo.hash_version += EXT4_SB(dir->i_sb)->s_hash_unsigned;
hinfo.seed = EXT4_SB(dir->i_sb)->s_hash_seed;
ext4fs_dirhash(name, namelen, &hinfo);
frame = frames;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 0ef4a1a..e191ce6 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2116,6 +2116,21 @@ 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;
+ i = le32_to_cpu(es->s_flags);
+ if (i & EXT2_FLAGS_UNSIGNED_HASH)
+ sbi->s_hash_unsigned = 3;
+ else if ((i & EXT2_FLAGS_SIGNED_HASH) == 0) {
+ char c;
+
+ c = (char) 255;
+ if (((int) c) == -1) {
+ es->s_flags |= cpu_to_le32(EXT2_FLAGS_SIGNED_HASH);
+ } else {
+ es->s_flags |= cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH);
+ sbi->s_hash_unsigned = 3;
+ }
+ sb->s_dirt = 1;
+ }

if (sbi->s_blocks_per_group > blocksize * 8) {
printk(KERN_ERR
--
1.5.6.1.205.ge2c7.dirty