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Subject: Re: Btrfs disk layout question
To: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>,
        Chris Murphy <lists@colorremedies.com>,
        Adam Borowski <kilobyte@angband.pl>
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Cc: Amin Hassani <ahassani@chromium.org>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>
From: Andrei Borzenkov <arvidjaar@gmail.com>
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Date: Wed, 12 Apr 2017 19:44:00 +0300
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12.04.2017 14:20, Austin S. Hemmelgarn пишет:
> On 2017-04-12 00:18, Chris Murphy wrote:
>> On Tue, Apr 11, 2017 at 3:00 PM, Adam Borowski <kilobyte@angband.pl>
>> wrote:
>>> On Tue, Apr 11, 2017 at 12:15:32PM -0700, Amin Hassani wrote:
>>>> I am working on a project with Btrfs and I was wondering if there is
>>>> any way to see the disk layout of the btrfs image. Let's assume I have
>>>> a read-only btrfs image with compression on and only using one disk
>>>> (no raid or anything). Is it possible to get a set of offset-lengths
>>>> for each file
>>>
>>> While btrfs-specific ioctls give more information, you might want to
>>> look at
>>> FIEMAP (Documentation/filesystems/fiemap.txt) as it works on most
>>> filesystems, not just btrfs.  One interface to FIEMAP is provided in
>>> "/usr/sbin/filefrag -v".
>>
>> Good idea. Although, on Btrfs I'm pretty sure it reports the Btrfs
>> (internal) logical addressing; not the actual physical sector address
>> on the drive. So it depends on what the original poster is trying to
>> discover.
>>
> That said, there is a tool to translate that back, and depending on how
> detailed you want to get, that may be more efficient than debug tree.

Could you give pointer to this tool? I use filefrag on bootinfoscript to
display physical disk offset of files of interest to bootloader. I was
not aware it shows logical offset which makes it kinda pointless.