From: Adam Borowski <kilobyte@angband.pl>
To: Mark Fasheh <mfasheh@suse.de>
Cc: Chris Mason <clm@fb.com>, Josef Bacik <jbacik@fb.com>,
David Sterba <dsterba@suse.com>,
linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] btrfs,vfs: allow FILE_EXTENT_SAME on a file opened ro
Date: Fri, 27 May 2016 02:48:11 +0200 [thread overview]
Message-ID: <20160527004811.GA30490@angband.pl> (raw)
In-Reply-To: <20160527000401.GW7633@wotan.suse.de>
On Thu, May 26, 2016 at 05:04:01PM -0700, Mark Fasheh wrote:
> On Fri, May 20, 2016 at 05:45:12AM +0200, Adam Borowski wrote:
> > (Only btrfs currently implements dedupe_file_range.)
> >
> > Instead of checking the mode of the file descriptor, let's check whether
> > it could have been opened rw. This allows fixing failures when deduping
> > a live system: anyone trying to exec a file currently being deduped gets
> > ETXTBSY.
> >
> > Issuing this ioctl on a ro file was already allowed for root/cap.
>
> Hi Adam, this patch seems reasonable to me but I have to admit to being
> worried about 'unintended consequences'. I poked around the code in fs/ for
> a bit and saw mostly checks against file open mode.
I can't think of any unintended consequences:
* root already could dedupe a file opened ro, so the code can handle that
* a file being open ro but you having rw rights means you could have opened
it rw
There are details related to inode_permission() I admit I don't fully
understand but I believe those don't really matter as reasons for not just
allowing FILE_EXTENT_SAME for anyone who can read the file are quite
far-fetched.
> It might be that dedupe is a special case due to the potential for longer
> running operations, but theoretically you'd see the same problem if trying
> to exec against a file being cloned too, correct? If that's the case then
> I wonder how this issue gets solved for other ioctls.
Clone is a destructive operation that overwrites the file. FILE_EXTENT_SAME
on the other hand makes no changes to the Posix view of the file, just to
its internal representation.
Meow!
--
An imaginary friend squared is a real enemy.
next prev parent reply other threads:[~2016-05-27 0:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-20 3:45 [PATCH] btrfs,vfs: allow FILE_EXTENT_SAME on a file opened ro Adam Borowski
2016-05-26 22:57 ` Adam Borowski
2016-05-27 0:04 ` Mark Fasheh
2016-05-27 0:48 ` Adam Borowski [this message]
2016-05-28 1:59 ` Zygo Blaxell
2016-05-29 0:21 ` Adam Borowski
2016-05-29 0:56 ` Zygo Blaxell
2016-05-29 6:53 ` Andrei Borzenkov
2016-05-30 12:24 ` Adam Borowski
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=20160527004811.GA30490@angband.pl \
--to=kilobyte@angband.pl \
--cc=clm@fb.com \
--cc=dsterba@suse.com \
--cc=jbacik@fb.com \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=mfasheh@suse.de \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.