kernel/linux.git/fs/ext4/hash.c, branch v7.2-rc2

ext4: improve str2hashbuf by processing 4-byte chunks and removing function pointers

2026-06-03T14:30:15+00:00

The original byte-by-byte implementation with modulo checks is less efficient. Refactor str2hashbuf_unsigned() and str2hashbuf_signed() to process input in explicit 4-byte chunks instead of using a modulus-based loop to emit words byte by byte. Additionally, the use of function pointers for selecting the appropriate str2hashbuf implementation has been removed. Instead, the functions are directly invoked based on the hash type, eliminating the overhead of dynamic function calls. Performance test (x86_64, Intel Core i7-10700 @ 2.90GHz, average over 10000 runs, using kernel module for testing): len | orig_s | new_s | orig_u | new_u ----+--------+-------+--------+------- 1 | 70 | 71 | 63 | 63 8 | 68 | 64 | 64 | 62 32 | 75 | 70 | 75 | 63 64 | 96 | 71 | 100 | 68 255 | 192 | 108 | 187 | 84 This change improves performance, especially for larger input sizes. Signed-off-by: Guan-Chun Wu <409411716@gms.tku.edu.tw> Link: https://patch.msgid.link/20260531080019.3794809-3-409411716@gms.tku.edu.tw Signed-off-by: Theodore Ts'o

ext4: add Kunit coverage for directory hash computation

2026-06-03T14:30:15+00:00

Introduce Kunit tests for fs/ext4/hash.c to verify ext4fs_dirhash() across the legacy, half-MD4, and TEA hash variants. The tests cover empty, seeded hashing, and non-ASCII name handling. They also verify error paths, including invalid hash versions and SipHash without a configured key, and check that the signed and unsigned hash variants differ on non-ASCII input as expected. When CONFIG_UNICODE is enabled, the tests further verify casefolded-name hashing and the fallback behavior for invalid input. Co-developed-by: Chen Hao Yu Signed-off-by: Chen Hao Yu Signed-off-by: Guan-Chun Wu <409411716@gms.tku.edu.tw> Link: https://patch.msgid.link/20260531080019.3794809-2-409411716@gms.tku.edu.tw Signed-off-by: Theodore Ts'o

ext4: make error code in __ext4fs_dirhash() consistent.

2025-11-06T15:32:33+00:00

Currently __ext4fs_dirhash() returns -1 (-EPERM) if fscrypt doesn't have encryption key, which may confuse users. Make the error code here consistent with existing error code. Signed-off-by: Julian Sun Message-ID: <20251010095257.3008275-1-sunjunchao@bytedance.com> Signed-off-by: Theodore Ts'o

ext4: hash: simplify kzalloc(n * 1, ...) to kzalloc(n, ...)

2025-03-21T05:10:10+00:00

sizeof(char) evaluates to 1. Remove the churn. Signed-off-by: Ethan Carter Edwards Reviewed-by: Andreas Dilger Link: https://patch.msgid.link/20250316-ext4-hash-kcalloc-v2-1-2a99e93ec6e0@ethancedwards.com Signed-off-by: Theodore Ts'o

ext4: remove redundant checks of s_encoding

2023-08-27T15:27:13+00:00

Now that ext4 does not allow inodes with the casefold flag to be instantiated when unsupported, it's unnecessary to repeatedly check for support later on during random filesystem operations. Signed-off-by: Eric Biggers Link: https://lore.kernel.org/r/20230814182903.37267-3-ebiggers@kernel.org Signed-off-by: Theodore Ts'o

ext4: improve error handling from ext4_dirhash()

2023-05-13T22:05:05+00:00

The ext4_dirhash() will *almost* never fail, especially when the hash tree feature was first introduced. However, with the addition of support of encrypted, casefolded file names, that function can most certainly fail today. So make sure the callers of ext4_dirhash() properly check for failures, and reflect the errors back up to their callers. Cc: stable@kernel.org Link: https://lore.kernel.org/r/20230506142419.984260-1-tytso@mit.edu Reported-by: syzbot+394aa8a792cb99dbc837@syzkaller.appspotmail.com Reported-by: syzbot+344aaa8697ebd232bfc8@syzkaller.appspotmail.com Link: https://syzkaller.appspot.com/bug?id=db56459ea4ac4a676ae4b4678f633e55da005a9b Signed-off-by: Theodore Ts'o

unicode: clean up the Kconfig symbol confusion

2022-01-21T00:57:24+00:00

Turn the CONFIG_UNICODE symbol into a tristate that generates some always built in code and remove the confusing CONFIG_UNICODE_UTF8_DATA symbol. Note that a lot of the IS_ENABLED() checks could be turned from cpp statements into normal ifs, but this change is intended to be fairly mechanic, so that should be cleaned up later. Fixes: 2b3d04787012 ("unicode: Add utf8-data module") Reported-by: Linus Torvalds Reviewed-by: Eric Biggers Signed-off-by: Christoph Hellwig Signed-off-by: Gabriel Krisman Bertazi

ext4: handle casefolding with encryption

2021-04-06T02:04:20+00:00

This adds support for encryption with casefolding. Since the name on disk is case preserving, and also encrypted, we can no longer just recompute the hash on the fly. Additionally, to avoid leaking extra information from the hash of the unencrypted name, we use siphash via an fscrypt v2 policy. The hash is stored at the end of the directory entry for all entries inside of an encrypted and casefolded directory apart from those that deal with '.' and '..'. This way, the change is backwards compatible with existing ext4 filesystems. [ Changed to advertise this feature via the file: /sys/fs/ext4/features/encrypted_casefold -- TYT ] Signed-off-by: Daniel Rosenberg Reviewed-by: Andreas Dilger Link: https://lore.kernel.org/r/20210319073414.1381041-2-drosen@google.com Signed-off-by: Theodore Ts'o

ext4: use generic casefolding support

2020-10-28T17:43:13+00:00

This switches ext4 over to the generic support provided in libfs. Since casefolded dentries behave the same in ext4 and f2fs, we decrease the maintenance burden by unifying them, and any optimizations will immediately apply to both. Signed-off-by: Daniel Rosenberg Reviewed-by: Eric Biggers Link: https://lore.kernel.org/r/20201028050820.1636571-1-drosen@google.com Signed-off-by: Theodore Ts'o

ext4: change to use fallthrough macro

2020-08-18T18:27:40+00:00

Change to use fallthrough macro in switch case. Signed-off-by: Shijie Luo Reviewed-by: Ritesh Harjani Link: https://lore.kernel.org/r/20200810114435.24182-1-luoshijie1@huawei.com Signed-off-by: Theodore Ts'o