This series introduces a generic Base64 encoder/decoder to the kernel
library, eliminating duplicated implementations and delivering significant
performance improvements.

The Base64 API has been extended to support multiple variants (Standard,
URL-safe, and IMAP) as defined in RFC 4648 and RFC 3501. The API now takes
a variant parameter and an option to control padding. As part of this
series, users are migrated to the new interface while preserving their
specific formats: fscrypt now uses BASE64_URLSAFE, Ceph uses BASE64_IMAP,
and NVMe is updated to BASE64_STD.

On the encoder side, the implementation processes input in 3-byte blocks,
mapping 24 bits directly to 4 output symbols. This avoids bit-by-bit
streaming and reduces loop overhead, achieving about a 2.7x speedup compared
to previous implementations.

On the decoder side, replace strchr() lookups with per-variant reverse tables
and process input in 4-character groups. Each group is mapped to numeric values
and combined into 3 bytes. Padded and unpadded forms are validated explicitly,
rejecting invalid '=' usage and enforcing tail rules. This improves throughput
by ~23-28x.

Thanks,
Guan-Chun Wu

---

v2 -> v3:
  - lib/base64: introduce enum base64_variant { BASE64_STD, BASE64_URLSAFE,
    BASE64_IMAP } and change the API to take this enum instead of a
    caller-supplied 64-character table.
  - lib/base64: add per-variant reverse lookup tables and update the decoder
    to use table lookups instead of strchr().
  - tests: add URLSAFE/IMAP checks (no '=' allowed) and keep STD as the
    main corpus.
  - users: update call sites to explicit variants (fscrypt=BASE64_URLSAFE,
    ceph=BASE64_IMAP, nvme-auth=BASE64_STD) while preserving formats.

---

Guan-Chun Wu (4):
  lib/base64: rework encode/decode for speed and stricter validation
  lib: add KUnit tests for base64 encoding/decoding
  fscrypt: replace local base64url helpers with lib/base64
  ceph: replace local base64 helpers with lib/base64

Kuan-Wei Chiu (2):
  lib/base64: Add support for multiple variants
  lib/base64: Optimize base64_decode() with reverse lookup tables

 drivers/nvme/common/auth.c |   4 +-
 fs/ceph/crypto.c           |  60 +-------
 fs/ceph/crypto.h           |   6 +-
 fs/ceph/dir.c              |   5 +-
 fs/ceph/inode.c            |   2 +-
 fs/crypto/fname.c          |  89 +----------
 include/linux/base64.h     |  10 +-
 lib/Kconfig.debug          |  19 ++-
 lib/base64.c               | 241 +++++++++++++++++++++++-------
 lib/tests/Makefile         |   1 +
 lib/tests/base64_kunit.c   | 294 +++++++++++++++++++++++++++++++++++++
 11 files changed, 525 insertions(+), 206 deletions(-)
 create mode 100644 lib/tests/base64_kunit.c

-- 
2.34.1