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    Subject[v2 PATCH] fscrypt: Allow modular crypto algorithms
    On Sat, Dec 21, 2019 at 05:44:28PM -0600, Eric Biggers wrote:
    >
    > I'm not sure this is a good idea, since there will probably need to be more
    > places where built-in code calls into fs/crypto/ too.

    Clearly it's going to be too much trouble for now. I may revisit
    this once the fscrypt code has settled down a little.

    However, we can at least build the algorithms as modules, like this:

    ---8<---
    The commit 643fa9612bf1 ("fscrypt: remove filesystem specific
    build config option") removed modular support for fs/crypto. This
    causes the Crypto API to be built-in whenever fscrypt is enabled.
    This makes it very difficult for me to test modular builds of
    the Crypto API without disabling fscrypt which is a pain.

    As fscrypt is still evolving and it's developing new ties with the
    fs layer, it's hard to build it as a module for now.

    However, the actual algorithms are not required until a filesystem
    is mounted. Therefore we can allow them to be built as modules.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

    diff --git a/fs/crypto/Kconfig b/fs/crypto/Kconfig
    index ff5a1746cbae..ae929fbc0f29 100644
    --- a/fs/crypto/Kconfig
    +++ b/fs/crypto/Kconfig
    @@ -1,7 +1,19 @@
    # SPDX-License-Identifier: GPL-2.0-only
    config FS_ENCRYPTION
    bool "FS Encryption (Per-file encryption)"
    + select KEYS
    select CRYPTO
    + select CRYPTO_SKCIPHER
    + select CRYPTO_HASH
    + help
    + Enable encryption of files and directories. This
    + feature is similar to ecryptfs, but it is more memory
    + efficient since it avoids caching the encrypted and
    + decrypted pages in the page cache. Currently Ext4,
    + F2FS and UBIFS make use of this feature.
    +
    +config FS_ENCRYPTION_TRI
    + tristate
    select CRYPTO_AES
    select CRYPTO_CBC
    select CRYPTO_ECB
    @@ -9,10 +21,3 @@ config FS_ENCRYPTION
    select CRYPTO_CTS
    select CRYPTO_SHA512
    select CRYPTO_HMAC
    - select KEYS
    - help
    - Enable encryption of files and directories. This
    - feature is similar to ecryptfs, but it is more memory
    - efficient since it avoids caching the encrypted and
    - decrypted pages in the page cache. Currently Ext4,
    - F2FS and UBIFS make use of this feature.
    diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
    index ef42ab040905..5de0bcc50d37 100644
    --- a/fs/ext4/Kconfig
    +++ b/fs/ext4/Kconfig
    @@ -10,6 +10,7 @@ config EXT3_FS
    select CRC16
    select CRYPTO
    select CRYPTO_CRC32C
    + select FS_ENCRYPTION_TRI if FS_ENCRYPTION
    help
    This config option is here only for backward compatibility. ext3
    filesystem is now handled by the ext4 driver.
    diff --git a/fs/f2fs/Kconfig b/fs/f2fs/Kconfig
    index 652fd2e2b23d..9ccaec60af47 100644
    --- a/fs/f2fs/Kconfig
    +++ b/fs/f2fs/Kconfig
    @@ -6,6 +6,7 @@ config F2FS_FS
    select CRYPTO
    select CRYPTO_CRC32
    select F2FS_FS_XATTR if FS_ENCRYPTION
    + select FS_ENCRYPTION_TRI if FS_ENCRYPTION
    help
    F2FS is based on Log-structured File System (LFS), which supports
    versatile "flash-friendly" features. The design has been focused on
    diff --git a/fs/ubifs/Kconfig b/fs/ubifs/Kconfig
    index 69932bcfa920..ea2d43829c18 100644
    --- a/fs/ubifs/Kconfig
    +++ b/fs/ubifs/Kconfig
    @@ -12,6 +12,7 @@ config UBIFS_FS
    select CRYPTO_ZSTD if UBIFS_FS_ZSTD
    select CRYPTO_HASH_INFO
    select UBIFS_FS_XATTR if FS_ENCRYPTION
    + select FS_ENCRYPTION_TRI if FS_ENCRYPTION
    depends on MTD_UBI
    help
    UBIFS is a file system for flash devices which works on top of UBI.
    --
    Email: Herbert Xu <herbert@gondor.apana.org.au>
    Home Page: http://gondor.apana.org.au/~herbert/
    PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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