From: Christoph Hellwig <hch@infradead.org>
To: Demi Marie Obenour <demiobenour@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>,
Chris Laprise <tasket@posteo.net>,
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: Fri, 3 Oct 2025 00:44:47 -0700 [thread overview]
Message-ID: <aN9-7wrgxqew1qRI@infradead.org> (raw)
In-Reply-To: <693793db-3431-48b3-8913-aadb86bc4ebc@gmail.com>
On Mon, Sep 29, 2025 at 07:55:22PM -0400, Demi Marie Obenour wrote:
> Can two extents have the same offset on disk but different logical contents?
> For XFS that seems impossible unless a realtime device is involved, which
> is not the case here.
Only with the RT device. But again that is insider knowledge and not an
API exposed to applications. More importantly the offset can change
underneath without any notice to the application.
> Is it easier if one requires the filesystem to be read-only? Taking a
> device-mapper snapshot (thin or CoW) before the backup is not too onerous,
> at least if the filesystem is already on an LVM LV.
At least that locks out other changes. But it is a rather opaque setup.
next prev parent reply other threads:[~2025-10-03 7:44 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
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 [this message]
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=aN9-7wrgxqew1qRI@infradead.org \
--to=hch@infradead.org \
--cc=demiobenour@gmail.com \
--cc=linux-btrfs@vger.kernel.org \
--cc=tasket@posteo.net \
/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).