From: Christoph Hellwig <hch@lst.de>
To: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: Andreas Dilger <adilger@dilger.ca>,
David Howells <dhowells@redhat.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>, Christoph Hellwig <hch@lst.de>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
David Sterba <dsterba@suse.com>,
linux-ext4 <linux-ext4@vger.kernel.org>,
linux-xfs <linux-xfs@vger.kernel.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: Problems with determining data presence by examining extents?
Date: Wed, 15 Jan 2020 14:31:01 +0100 [thread overview]
Message-ID: <20200115133101.GA28583@lst.de> (raw)
In-Reply-To: <afa71c13-4f99-747a-54ec-579f11f066a0@gmx.com>
On Wed, Jan 15, 2020 at 09:10:44PM +0800, Qu Wenruo wrote:
> > That allows userspace to distinguish fe_physical addresses that may be
> > on different devices. This isn't in the kernel yet, since it is mostly
> > useful only for Btrfs and nobody has implemented it there. I can give
> > you details if working on this for Btrfs is of interest to you.
>
> IMHO it's not good enough.
>
> The concern is, one extent can exist on multiple devices (mirrors for
> RAID1/RAID10/RAID1C2/RAID1C3, or stripes for RAID5/6).
> I didn't see how it can be easily implemented even with extra fields.
>
> And even we implement it, it can be too complex or bug prune to fill
> per-device info.
It's also completely bogus for the use cases to start with. fiemap
is a debug tool reporting the file system layout. Using it for anything
related to actual data storage and data integrity is a receipe for
disaster. As said the right thing for the use case would be something
like the NFS READ_PLUS operation. If we can't get that easily it can
be emulated using lseek SEEK_DATA / SEEK_HOLE assuming no other thread
could be writing to the file, or the raciness doesn't matter.
next prev parent reply other threads:[~2020-01-15 13:31 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-14 16:48 Problems with determining data presence by examining extents? David Howells
2020-01-14 22:49 ` Theodore Y. Ts'o
2020-01-15 3:54 ` Qu Wenruo
2020-01-15 12:46 ` Andreas Dilger
2020-01-15 13:10 ` Qu Wenruo
2020-01-15 13:31 ` Christoph Hellwig [this message]
2020-01-15 19:48 ` Andreas Dilger
2020-01-16 10:16 ` Christoph Hellwig
2020-01-15 20:55 ` David Howells
2020-01-15 22:11 ` Andreas Dilger
2020-01-15 23:09 ` David Howells
2020-01-26 18:19 ` Zygo Blaxell
2020-01-15 14:35 ` David Howells
2020-01-15 14:48 ` Christoph Hellwig
2020-01-15 14:59 ` David Howells
2020-01-16 10:13 ` Christoph Hellwig
2020-01-17 16:43 ` David Howells
2020-01-15 14:20 ` David Howells
2020-01-15 8:38 ` Christoph Hellwig
2020-01-15 13:50 ` David Howells
2020-01-15 14:05 ` David Howells
2020-01-15 14:24 ` Qu Wenruo
2020-01-15 14:50 ` David Howells
2020-01-15 14:15 ` David Howells
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=20200115133101.GA28583@lst.de \
--to=hch@lst.de \
--cc=adilger@dilger.ca \
--cc=clm@fb.com \
--cc=darrick.wong@oracle.com \
--cc=dhowells@redhat.com \
--cc=dsterba@suse.com \
--cc=josef@toxicpanda.com \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-xfs@vger.kernel.org \
--cc=quwenruo.btrfs@gmx.com \
--cc=tytso@mit.edu \
--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).