From: Christoph Hellwig <hch@infradead.org>
To: Demi Marie Obenour <demiobenour@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>, linux-btrfs@vger.kernel.org
Subject: Re: Can the output of FIEMAP on BTRFS be used to check if a file and its reflink copy might have diverged?
Date: Mon, 22 Sep 2025 10:31:34 -0700 [thread overview]
Message-ID: <aNGH9s0xoIg9Isk5@infradead.org> (raw)
In-Reply-To: <7b756bc3-fae4-4cbb-99a1-117880269269@gmail.com>
On Mon, Sep 22, 2025 at 01:30:36PM -0400, Demi Marie Obenour wrote:
> On 9/22/25 13:20, Christoph Hellwig wrote:
> > On Mon, Sep 22, 2025 at 01:18:52PM -0400, Demi Marie Obenour wrote:
> >> Is it safe on XFS if there is no RT device and both files have been
> >> fsync'd and are not modified by userspace? I believe this is the case
> >> here: reflinks are used to snapshot the files before they are looked at.
> >
> > No. Yo ucan still have defragementation or garbage collection going on
> > underneath.
>
> Can these be prevented by mounting a read-only device-mapper snapshot,
> replaying the journal, and then doing processing in userspace on the
> block device?
Which part of "looking at FIEMAP output except for debugging the file
system is highly dangerous" did you not understand? Don't do it, you
will lose data eventually.
next prev parent reply other threads:[~2025-09-22 17:31 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-22 0:07 Can the output of FIEMAP on BTRFS be used to check if a file and its reflink copy might have diverged? Demi Marie Obenour
2025-09-22 0:50 ` Qu Wenruo
2025-09-22 18:24 ` Demi Marie Obenour
2025-09-22 21:38 ` Qu Wenruo
2025-09-22 16:48 ` Christoph Hellwig
2025-09-22 17:18 ` Demi Marie Obenour
2025-09-22 17:20 ` Christoph Hellwig
2025-09-22 17:30 ` Demi Marie Obenour
2025-09-22 17:31 ` Christoph Hellwig [this message]
2025-09-22 17:54 ` Demi Marie Obenour
2025-09-29 8:50 ` Christoph Hellwig
2025-09-29 23:56 ` Demi Marie Obenour
2025-09-30 1:34 ` Demi Marie Obenour
2025-10-03 7:45 ` Christoph Hellwig
2025-09-22 23:25 ` Chris Laprise
2025-09-29 8:49 ` Christoph Hellwig
2025-09-29 23:55 ` Demi Marie Obenour
2025-10-03 7:44 ` Christoph Hellwig
2025-10-04 1:09 ` Demi Marie Obenour
2025-10-04 1:43 ` Chris Laprise
2025-10-04 4:51 ` Christoph Hellwig
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=aNGH9s0xoIg9Isk5@infradead.org \
--to=hch@infradead.org \
--cc=demiobenour@gmail.com \
--cc=linux-btrfs@vger.kernel.org \
/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).