Date:   Fri, 13 Sep 2019 08:02:52 +0530
From:   Chandan Rajendra <chandan@...ux.ibm.com>
To:     linux-fsdevel@...r.kernel.org, viro@...iv.linux.org.uk,
        tytso@....edu
Cc:     linux-ext4@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        adilger.kernel@...ger.ca, ebiggers@...nel.org, hch@...radead.org,
        chandanrlinux@...il.com
Subject: Re: [PATCH RESEND V5 0/7] Consolidate FS read I/O callbacks code

On Tuesday, September 10, 2019 9:21 PM Chandan Rajendra wrote: 
> This patchset moves the "FS read I/O callbacks" code into a file of its
> own (i.e. fs/read_callbacks.c) and modifies the generic
> do_mpage_readpge() to make use of the functionality provided.
> 
> "FS read I/O callbacks" code implements the state machine that needs
> to be executed after reading data from files that are encrypted and/or
> have verity metadata associated with them.
> 
> With these changes in place, the patchset changes Ext4 to use
> mpage_readpage[s] instead of its own custom ext4_readpage[s]()
> functions. This is done to reduce duplication of code across
> filesystems. Also, "FS read I/O callbacks" source files will be built
> only if CONFIG_FS_ENCRYPTION is enabled.
> 
> The patchset also modifies fs/buffer.c to get file
> encryption/decryption to work with subpage-sized blocks.
> 
> The patches can also be obtained from
> https://github.com/chandanr/linux.git at branch subpage-encryption-v5.
>

Al Viro and Ted,
Can you please take a look at this patchset? I have addressed all the review
comments that was provided up until version V4.

Ted,
Please let me know the if there is anything remaining from my side to get Ext4
encryption working in subpage blocksize scenario.


> Changelog:
> V4 -> V5:
>    1. Since F2FS uses its own workqueue and also since its
>       decompression logic isn't an fs independent entity like fscrypt or
>       fsverity, this patchset drops support for F2FS.
>       The patchset still helps in removing a copy of
>       do_mpage_readpage() from Ext4 (i.e. ext4_readpage()) and also
>       prevents a copy of block_read_full_page() from being added into
>       Ext4 by adding support to "read callbacks" API invocations into
>       block_read_full_page().
> 
> V3 -> V4:
>    1. A new buffer_head flag (i.e. BH_Read_Cb) is introduced to reliably
>       check if a buffer head's content has to be decrypted.
>    2. Fix layering violation. Now the code flow for decryption happens as shown below,
>       FS => read callbacks => fscrypt
>    3. Select FS_READ_CALLBACKS from FS specific kconfig file if FS_ENCRYPTION
>       is enabled.
>    4. Make 'struct read_callbacks_ctx' an opaque structure.
>    5. Make use of FS' endio function rather than implementing one in read
>       callbacks.
>    6. Make read_callbacks.h self-contained.
>    7. Split patchset to separate out ext4 and f2fs changes.
>    
> V2 -> V3:
> 1. Split the V2 patch "Consolidate 'read callbacks' into a new file" into
>    three patches,
>    - Introduce the read_callbacks functionality.
>    - Convert encryption to use read_callbacks.
>    - Remove union from struct fscrypt_context.
> 2. fs/Kconfig
>    Do not explicitly set the default value of 'n' for FS_READ_CALLBACKS.
> 3. fs/crypto/Kconfig
>    Select CONFIG_FS_READ_CALLBACKS only if CONFIG_BLOCK is selected.
> 4. Remove verity associated code in read_callbacks code.
> 5. Introduce a callback argument to read_callbacks_setup() function
>    which gets invoked for each page for bio. F2FS uses this to perform
>    custom operations like decrementing the value of f2fs_sb_info->nr_pages[].
> 6. Encapsulate the details of "read callbacks" (e.g. Usage of "struct
>    read_callbacks *ctx") within its own functions. When CONFIG_FS_READ_CALLBACKS
>    is set to 'n', the corresponding stub functions return approriate error
>    values.
> 7. Split fscrypt_decrypt() function into fscrypt_decrypt_bio() and
>    fscrypt_decrypt_bh().
> 8. Split end_read_callbacks() function into end_read_callbacks_bio() and
>    end_read_callbacks_bh().
> 
> V1 -> V2:
> 1. Removed the phrase "post_read_process" from file names and
>    functions. Instead we now use the phrase "read_callbacks" in its
>    place.
> 2. When performing changes associated with (1), the changes made by
>    the patch "Remove the term 'bio' from post read processing" are
>    made in the earlier patch "Consolidate 'read callbacks' into a new
>    file". Hence the patch "Remove the term 'bio' from post read
>    processing" is removed from the patchset.
> 
> RFC V2 -> V1:
> 1. Test and verify FS_CFLG_OWN_PAGES subset of fscrypt_encrypt_page()
>    code by executing fstests on UBIFS.
> 2. Implement F2fs function call back to check if the contents of a
>    page holding a verity file's data needs to be verified.
> 
> RFC V1 -> RFC V2:
> 1. Describe the purpose of "Post processing code" in the cover letter.
> 2. Fix build errors when CONFIG_FS_VERITY is enabled.
> 
> Chandan Rajendra (7):
>   buffer_head: Introduce BH_Read_Cb flag
>   FS: Introduce read callbacks
>   fs/mpage.c: Integrate read callbacks
>   fs/buffer.c: add decryption support via read_callbacks
>   ext4: Wire up ext4_readpage[s] to use mpage_readpage[s]
>   ext4: Enable encryption for subpage-sized blocks
>   fscrypt: remove struct fscrypt_ctx
> 
>  Documentation/filesystems/fscrypt.rst |   4 +-
>  fs/Kconfig                            |   3 +
>  fs/Makefile                           |   1 +
>  fs/buffer.c                           |  33 ++-
>  fs/crypto/bio.c                       |  18 --
>  fs/crypto/crypto.c                    |  89 +-------
>  fs/crypto/fscrypt_private.h           |   3 -
>  fs/ext4/Kconfig                       |   1 +
>  fs/ext4/Makefile                      |   2 +-
>  fs/ext4/inode.c                       |   5 +-
>  fs/ext4/readpage.c                    | 295 --------------------------
>  fs/ext4/super.c                       |   7 -
>  fs/f2fs/Kconfig                       |   1 +
>  fs/mpage.c                            |  24 ++-
>  fs/read_callbacks.c                   | 285 +++++++++++++++++++++++++
>  include/linux/buffer_head.h           |   2 +
>  include/linux/fscrypt.h               |  32 ---
>  include/linux/read_callbacks.h        |  48 +++++
>  18 files changed, 391 insertions(+), 462 deletions(-)
>  delete mode 100644 fs/ext4/readpage.c
>  create mode 100644 fs/read_callbacks.c
>  create mode 100644 include/linux/read_callbacks.h
> 
> 


-- 
chandan

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