linux-ext4 - Re: [RFC PATCH V3 07/12] mpage_readpage[s]: Introduce post process callback parameters

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Date:   Tue, 29 May 2018 08:34:21 +0530
From:   Chandan Rajendra <chandan@...ux.vnet.ibm.com>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     linux-fscrypt@...r.kernel.org, ebiggers3@...il.com,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH V3 07/12] mpage_readpage[s]: Introduce post process callback parameters

On Tuesday, May 29, 2018 1:04:37 AM IST Theodore Y. Ts'o wrote:
> On Mon, May 28, 2018 at 11:05:52AM +0530, Chandan Rajendra wrote:
> > > Can you describe more of what you are doing here; specifically, you
> > > deleted all of fs/ext4/readpage.c --- was this because you moved
> > > functionality back into fs/mpage.c?  Did you make sure all of the
> > > local changes in fs/ext4/readpage was moved back to fs/mpage.c?
> > > 
> > > If the goal is to refactor code to remove the need for
> > > fs/ext4/readpage.c, you should probably make that be the first patch
> > > as a prerequisite patch.  And we then need to make sure we don't
> > > accidentally break anyone else who might be using fs/mpage.c.  Saying
> > > a bit more about why you think the refactor is a good thing would also
> > > be useful.
> > 
> > I will split this patch into two as suggested by you. Also, I will update 
> > the commit messages.
> 
> Note that I was planning on making changes to fs/ext4/readpage.c as
> part of integrating fsverity[1][2] support into ext4.  Basically, I
> need to do something like [3] to fs/ext4/readpage.c.
> 
> [1] https://www.spinics.net/lists/linux-fsdevel/msg121182.html
> [2] https://www.youtube.com/watch?v=GlEWcVuRbNA
> [3] https://git.kernel.org/pub/scm/linux/kernel/git/mhalcrow/linux.git/commit/?h=fs-verity-dev&id=827faba05972517f49fa2f2aaf272150f5766af2
> 
> Which is why I'm really interested in your reasoning for why you
> propose to drop fs/ext4/readpage.c.  :-)
> 

The first patchset to support encryption in subpage-blocksize scenario copied
the block_read_full_page() from fs/buffer.c to ext4/readpage.c and had made
changes required to support encryption in that function. However, the
conclusion was to not create copies of existing code but rather add support
for decryption inside generic mpage_readpage[s] functions. Hence this patchset
implements the required decryption logic in the generic mpage_readpage[s]
functions. Since this makes the code in ext4/readpage.c redundant, I had
decided to delete the ext4/readpage.c.

-- 
chandan