Date:	Wed, 13 May 2015 18:56:43 -0700
From:	Jaegeuk Kim <jaegeuk@...nel.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [PATCH 03/18] f2fs crypto: declare some definitions for f2fs
 encryption feature

On Thu, May 14, 2015 at 10:37:21AM +1000, Dave Chinner wrote:
> On Tue, May 12, 2015 at 11:48:02PM -0700, Jaegeuk Kim wrote:
> > On Wed, May 13, 2015 at 12:02:08PM +1000, Dave Chinner wrote:
> > > On Fri, May 08, 2015 at 09:20:38PM -0700, Jaegeuk Kim wrote:
> > > > This definitions will be used by inode and superblock for encyption.
> > > 
> > > How much of this crypto stuff is common with or only slightly
> > > modified from the ext4 code?  Is the behaviour and features the
> > > same? Is the user API and management tools the same?
> > > 
> > > IMO, if there is any amount of overlap, then we should be
> > > implementing this stuff as generic code, not propagating the same
> > > code through multiple filesystems via copy-n-paste-n-modify. This
> > > will simply end up with diverging code, different bugs and feature
> > > sets, and none of the implementations will get the review and
> > > maintenance they really require...
> > > 
> > > And, FWIW, this is the reason why I originally asked for the ext4
> > > encryption code to be pulled up to the VFS: precisely so we didn't
> > > end up with a rapid proliferation of individual in-filesystem
> > > encryption implementations that are all slightly different...
> > 
> > Totally agreed!
> > 
> > AFAIK, Ted wants to push the codes as a crypto library into fs/ finally, so
> > I believe most part of crypto codes are common.
> 
> Can I suggest fs/crypto/ if there are going to be multiple files?

No problem at all. I'll do.

> 
> > But, in order to realize that quickly, Ted implemented the feature to finalize
> > on-disk and in-memory design in EXT4 as a first step.
> > Then, I've been catching up and validating its design by implementing it in
> > F2FS, which also intends to figure out what crypto codes can be exactly common.
> 
> Excellent. That will make it easier and less error prone for other
> filesystems to implement it, too!
> 
> > As Ted mentioned before, since next android version tries to use per-file
> > encryption, F2FS also needs to support it as quick as possible likewise EXT4.
> 
> Fair enough.
> 
> > Meanwhile, surely I've been working on writing patches to push them into fs/;
> > currenlty, I did for cryto.c and will do for crypto_key.c and crypto_fname.c.
> > But, it needs to think about crypto_policy.c differently, since it may depend
> > on how each filesystem stores the policy information respectively; we cannot
> > push all the filesystems should use xattrs, right?
> 
> All filesystems likely to implement per-file crypto support xattrs,
> and this is exactly what xattrs are designed for. e.g. we already
> require xattrs for generic security labels, ACLs, etc. Hence
> per-file crypto information should also use a common, shared xattr
> format. That way it only needs to be implemented once in the generic
> code and there's very little (hopefully nothing!) each filesystem
> has to customise to store the crypto information for each file.

Ok, I see. Let me take a look at that too.
Thank you for sharing your thoughts. :)

> 
> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@...morbit.com
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