From: Adam Borowski <kilobyte@angband.pl>
To: Eric Wheeler <btrfs@lists.ewheeler.net>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: How can I get blockdev offsets of btrfs chunks for a file?
Date: Sat, 16 Jul 2016 02:13:36 +0200 [thread overview]
Message-ID: <20160716001336.GA10651@angband.pl> (raw)
In-Reply-To: <alpine.LRH.2.11.1607151621220.20548@mail.ewheeler.net>
On Fri, Jul 15, 2016 at 04:21:31PM -0700, Eric Wheeler wrote:
> We do btrfs subvolume snapshots over time for backups. I would like to
> traverse the files in the subvolumes and find the total unique chunk count
> to calculate total space for a set of subvolumes.
>
> This sounds kind of like the beginning of what a deduplicator would do,
> but I just want to count the blocks, so no submission for deduplication.
> I started looking at bedup and other deduplicator code, but the answer to
> this question wasn't obvious (to me, anyway).
>
> Questions:
>
> Is there an ioctl (or some other way) to get the block device offset for a
> file (or file offset) so I can count the unique occurances?
Yes, FIEMAP.
You can play with it via "/usr/sbin/filefrag -v". That /usr/sbin is
misleading -- FIEMAP doesn't require root, although its predecessor did need
that, https://bugs.debian.org/819923
> What API documentation should I review?
In kernel sources, Documentation/filesystems/fiemap.txt
Meow!
--
An imaginary friend squared is a real enemy.
next prev parent reply other threads:[~2016-07-16 0:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-15 23:21 How can I get blockdev offsets of btrfs chunks for a file? Eric Wheeler
2016-07-15 23:51 ` Tomasz Kusmierz
2016-07-16 0:13 ` Adam Borowski [this message]
2016-07-16 0:17 ` Hugo Mills
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