From mboxrd@z Thu Jan  1 00:00:00 1970
From: Omar Sandoval <osandov@osandov.com>
Subject: Re: [RFC PATCH 2/3] add RWF_ENCODED for writing compressed data
Date: Thu, 26 Sep 2019 10:46:09 -0700
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To: Colin Walters <walters@verbum.org>
Cc: Chris Mason <clm@fb.com>, Dave Chinner <david@fromorbit.com>, Jann Horn <jannh@google.com>, Aleksa Sarai <cyphar@cyphar.com>, Jens Axboe <axboe@kernel.dk>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>, Linux API <linux-api@vger.kernel.org>, Kernel Team <Kernel-team@fb.com>, Andy Lutomirski <luto@kernel.org>
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On Thu, Sep 26, 2019 at 08:17:12AM -0400, Colin Walters wrote:
> 
> 
> On Wed, Sep 25, 2019, at 10:56 AM, Chris Mason wrote:
> 
> > The data is verified while being decompressed, but that's a fairly large 
> > fuzzing surface (all of zstd, zlib, and lzo).  A lot of people will 
> > correctly argue that we already have that fuzzing surface today, but I'd 
> > rather not make a really easy way to stuff arbitrary bytes through the 
> > kernel decompression code until all the projects involved sign off.
> 
> Right.  So maybe have this start of as a BTRFS ioctl and require
> privileges?   I assume that's sufficient for what Omar wants.

That was the first version of this series, but Dave requested that I
make it generic [1].

> (Are there actually any other popular Linux filesystems that do transparent compression anyways?)

A scan over the kernel tree shows that a few other filesystems do
compression:

- jffs2
- pstore (if you can call that a filesystem)
- ubifs
- cramfs (read-only)
- erofs (read-only)
- squashfs (read-only)

None of the "mainstream" general-purpose filesystems have support, but
that was also the case for reflink/dedupe before XFS added support.

1: https://lore.kernel.org/linux-fsdevel/20190905021012.GL7777@dread.disaster.area/