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From: Andrei Borzenkov <arvidjaar@gmail.com>
To: Lennert Buytenhek <buytenh@wantstofly.org>, linux-btrfs@vger.kernel.org
Subject: Re: FS_IOC_FIEMAP fe_physical discrepancies on btrfs
Date: Sat, 27 Oct 2018 19:50:40 +0300	[thread overview]
Message-ID: <c8252c1b-abdb-1278-eec3-6fe0f5f69929@gmail.com> (raw)
In-Reply-To: <20181027154555.GH16768@wantstofly.org>

27.10.2018 18:45, Lennert Buytenhek пишет:
> Hello!
> 
> FS_IOC_FIEMAP on btrfs seems to be returning fe_physical values that
> don't always correspond to the actual on-disk data locations.  For some
> files the values match, but e.g. for this file:
> 
> # filefrag -v foo
> Filesystem type is: 9123683e
> File size of foo is 4096 (1 block of 4096 bytes)
>  ext:     logical_offset:        physical_offset: length:   expected: flags:
>    0:        0..       0:    5774454..   5774454:      1:             last,eof
> foo: 1 extent found
> #
> 
> The file data is actually on disk not in block 5774454 (0x581c76), but
> in block 6038646 (0x5c2476), an offset of +0x40800.  Is this expected
> behavior?  Googling didn't turn up much, apologies if this is an FAQ. :(
> 
> (This is on 4.18.16-200.fc28.x86_64, the current Fedora 28 kernel.)
> 

My understanding is that it returns logical block address in btrfs
address space. btrfs can span multiple devices so you will need to
convert extent address to (device,offset) pair if necessary.

  reply	other threads:[~2018-10-27 16:50 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-27 15:45 FS_IOC_FIEMAP fe_physical discrepancies on btrfs Lennert Buytenhek
2018-10-27 16:50 ` Andrei Borzenkov [this message]
2018-10-28  2:15 ` Qu Wenruo

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