linux-kernel - Re: [PATCH 3/6] direct-io: do not merge logically non-contiguous requests

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Message-ID: <AANLkTikwPL8-WefVIMF1ldTZpWVHvS1Lbh4YB8MZ4eu0@mail.gmail.com>
Date:	Fri, 21 May 2010 18:47:36 -0700
From:	Mike Fedyk <mfedyk@...efedyk.com>
To:	Josef Bacik <josef@...hat.com>
Cc:	linux-btrfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, hch@...radead.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 3/6] direct-io: do not merge logically non-contiguous 
	requests

On Fri, May 21, 2010 at 10:03 AM, Josef Bacik <josef@...hat.com> wrote:
> Btrfs cannot handle having logically non-contiguous requests submitted.  For
> example if you have
>
> Logical:  [0-4095][HOLE][8192-12287]
> Physical: [0-4095]      [4096-8191]
>
> Normally the DIO code would put these into the same BIO's.  The problem is we
> need to know exactly what offset is associated with what BIO so we can do our
> checksumming and unlocking properly, so putting them in the same BIO doesn't
> work.  So add another check where we submit the current BIO if the physical
> blocks are not contigous OR the logical blocks are not contiguous.
>
> Signed-off-by: Josef Bacik <josef@...hat.com>
> ---
>
> V1->V2
> -Be more verbose in the in-code comment
>
>  fs/direct-io.c |   20 ++++++++++++++++++--
>  1 files changed, 18 insertions(+), 2 deletions(-)
>

Btrfs has been pretty much self-contained (working well compiled
against 2.6.32 for example).  Is there a way that this wouldn't just
start silently breaking for people compiling the latest btrfs with
dkms against older kernels?
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