From: Amir Goldstein <amir73il@gmail.com>
To: Giuseppe Scrivano <gscrivan@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>,
Alexander Larsson <alexl@redhat.com>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
brauner@kernel.org, viro@zeniv.linux.org.uk,
Vivek Goyal <vgoyal@redhat.com>,
Miklos Szeredi <miklos@szeredi.hu>
Subject: Re: [PATCH v3 0/6] Composefs: an opportunistically sharing verified image filesystem
Date: Wed, 25 Jan 2023 14:46:59 +0200 [thread overview]
Message-ID: <CAOQ4uximBLqXDtq9vDhqR__1ctiiOMhMd03HCFUR_Bh_JFE-UQ@mail.gmail.com> (raw)
In-Reply-To: <87o7qmbxv4.fsf@redhat.com>
> >
> > Based on Alexander's explanation about the differences between overlayfs
> > lookup vs. composefs lookup of a regular "metacopy" file, I just need to
> > point out that the same optimization (lazy lookup of the lower data
> > file on open)
> > can be done in overlayfs as well.
> > (*) currently, overlayfs needs to lookup the lower file also for st_blocks.
> >
> > I am not saying that it should be done or that Miklos will agree to make
> > this change in overlayfs, but that seems to be the major difference.
> > getxattr may have some extra cost depending on in-inode xattr format
> > of erofs, but specifically, the metacopy getxattr can be avoided if this
> > is a special overlayfs RO mount that is marked as EVERYTHING IS
> > METACOPY.
> >
> > I don't expect you guys to now try to hack overlayfs and explore
> > this path to completion.
> > My expectation is that this information will be clearly visible to anyone
> > reviewing future submission, e.g.:
> >
> > - This is the comparison we ran...
> > - This is the reason that composefs gives better results...
> > - It MAY be possible to optimize erofs/overlayfs to get to similar results,
> > but we did not try to do that
> >
> > It is especially important IMO to get the ACK of both Gao and Miklos
> > on your analysis, because remember than when this thread started,
> > you did not know about the metacopy option and your main argument
> > was saving the time it takes to create the overlayfs layer files in the
> > filesystem, because you were missing some technical background on overlayfs.
>
> we knew about metacopy, which we already use in our tools to create
> mapped image copies when idmapped mounts are not available, and also
> knew about the other new features in overlayfs. For example, the
> "volatile" feature which was mentioned in your
> Overlayfs-containers-lpc-2020 talk, was only submitted upstream after
> begging Miklos and Vivek for months. I had a PoC that I used and tested
> locally and asked for their help to get it integrated at the file
> system layer, using seccomp for the same purpose would have been more
> complex and prone to errors when dealing with external bind mounts
> containing persistent data.
>
> The only missing bit, at least from my side, was to consider an image
> that contains only overlay metadata as something we could distribute.
>
I'm glad that I was able to point this out to you, because now the comparison
between the overlayfs and composefs options is more fair.
> I previously mentioned my wish of using it from a user namespace, the
> goal seems more challenging with EROFS or any other block devices. I
> don't know about the difficulty of getting overlay metacopy working in a
> user namespace, even though it would be helpful for other use cases as
> well.
>
There is no restriction of metacopy in user namespace.
overlayfs needs to be mounted with -o userxattr and the overlay
xattrs needs to use user.overlay. prefix.
w.r.t. the implied claim that composefs on-disk format is simple enough
so it could be made robust enough to avoid exploits, I will remain
silent and let others speak up, but I advise you to take cover,
because this is an explosive topic ;)
Thanks,
Amir.
next prev parent reply other threads:[~2023-01-25 12:47 UTC|newest]
Thread overview: 80+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-20 15:23 [PATCH v3 0/6] Composefs: an opportunistically sharing verified image filesystem Alexander Larsson
2023-01-20 15:23 ` [PATCH v3 1/6] fsverity: Export fsverity_get_digest Alexander Larsson
2023-01-20 15:23 ` [PATCH v3 2/6] composefs: Add on-disk layout header Alexander Larsson
2023-01-20 15:23 ` [PATCH v3 3/6] composefs: Add descriptor parsing code Alexander Larsson
2023-01-20 15:23 ` [PATCH v3 4/6] composefs: Add filesystem implementation Alexander Larsson
2023-01-20 15:23 ` [PATCH v3 5/6] composefs: Add documentation Alexander Larsson
2023-01-21 2:19 ` Bagas Sanjaya
2023-01-20 15:23 ` [PATCH v3 6/6] composefs: Add kconfig and build support Alexander Larsson
2023-01-20 19:44 ` [PATCH v3 0/6] Composefs: an opportunistically sharing verified image filesystem Amir Goldstein
2023-01-20 22:18 ` Giuseppe Scrivano
2023-01-21 3:08 ` Gao Xiang
2023-01-21 16:19 ` Giuseppe Scrivano
2023-01-21 17:15 ` Gao Xiang
2023-01-21 22:34 ` Giuseppe Scrivano
2023-01-22 0:39 ` Gao Xiang
2023-01-22 9:01 ` Giuseppe Scrivano
2023-01-22 9:32 ` Giuseppe Scrivano
2023-01-24 0:08 ` Gao Xiang
2023-01-21 10:57 ` Amir Goldstein
2023-01-21 15:01 ` Giuseppe Scrivano
2023-01-21 15:54 ` Amir Goldstein
2023-01-21 16:26 ` Gao Xiang
2023-01-23 17:56 ` Alexander Larsson
2023-01-23 23:59 ` Gao Xiang
2023-01-24 3:24 ` Amir Goldstein
2023-01-24 13:10 ` Alexander Larsson
2023-01-24 14:40 ` Gao Xiang
2023-01-24 19:06 ` Amir Goldstein
2023-01-25 4:18 ` Dave Chinner
2023-01-25 8:32 ` Amir Goldstein
2023-01-25 10:08 ` Alexander Larsson
2023-01-25 10:43 ` Amir Goldstein
2023-01-25 10:39 ` Giuseppe Scrivano
2023-01-25 11:17 ` Amir Goldstein
2023-01-25 12:30 ` Giuseppe Scrivano
2023-01-25 12:46 ` Amir Goldstein [this message]
2023-01-25 13:10 ` Giuseppe Scrivano
2023-01-25 18:07 ` Amir Goldstein
2023-01-25 19:45 ` Giuseppe Scrivano
2023-01-25 20:23 ` Amir Goldstein
2023-01-25 20:29 ` Amir Goldstein
2023-01-27 15:57 ` Vivek Goyal
2023-01-25 15:24 ` Christian Brauner
2023-01-25 16:05 ` Giuseppe Scrivano
2023-01-25 9:37 ` Alexander Larsson
2023-01-25 10:05 ` Gao Xiang
2023-01-25 10:15 ` Alexander Larsson
2023-01-27 10:24 ` Gao Xiang
2023-02-01 4:28 ` Jingbo Xu
2023-02-01 7:44 ` Amir Goldstein
2023-02-01 8:59 ` Jingbo Xu
2023-02-01 9:52 ` Alexander Larsson
2023-02-01 12:39 ` Jingbo Xu
2023-02-01 9:46 ` Alexander Larsson
2023-02-01 10:01 ` Gao Xiang
2023-02-01 11:22 ` Gao Xiang
2023-02-02 6:37 ` Amir Goldstein
2023-02-02 7:17 ` Gao Xiang
2023-02-02 7:37 ` Gao Xiang
2023-02-03 11:32 ` Alexander Larsson
2023-02-03 12:46 ` Amir Goldstein
2023-02-03 15:09 ` Gao Xiang
2023-02-05 19:06 ` Amir Goldstein
2023-02-06 7:59 ` Amir Goldstein
2023-02-06 10:35 ` Miklos Szeredi
2023-02-06 13:30 ` Amir Goldstein
2023-02-06 16:34 ` Miklos Szeredi
2023-02-06 17:16 ` Amir Goldstein
2023-02-06 18:17 ` Amir Goldstein
2023-02-06 19:32 ` Miklos Szeredi
2023-02-06 20:06 ` Amir Goldstein
2023-02-07 8:12 ` Alexander Larsson
2023-02-06 12:51 ` Alexander Larsson
2023-02-07 8:12 ` Jingbo Xu
2023-02-06 12:43 ` Alexander Larsson
2023-02-06 13:27 ` Gao Xiang
2023-02-06 15:31 ` Alexander Larsson
2023-02-01 12:06 ` Jingbo Xu
2023-02-02 4:57 ` Jingbo Xu
2023-02-02 4:59 ` Jingbo Xu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=CAOQ4uximBLqXDtq9vDhqR__1ctiiOMhMd03HCFUR_Bh_JFE-UQ@mail.gmail.com \
--to=amir73il@gmail.com \
--cc=alexl@redhat.com \
--cc=brauner@kernel.org \
--cc=david@fromorbit.com \
--cc=gscrivan@redhat.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=miklos@szeredi.hu \
--cc=vgoyal@redhat.com \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).