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Message-ID: <64c763540510070436s681a3e00q511fb68c1c876aa9@mail.gmail.com>
Date: Fri, 7 Oct 2005 17:06:37 +0530
From: Block Device <blockdevice@gmail.com>
Reply-To: Block Device <blockdevice@gmail.com>
To: Nikita Danilov <nikita@clusterfs.com>
Subject: Re: Block I/O Mystery
Cc: Linux Kernel Mailing List <Linux-Kernel@vger.kernel.org>
In-Reply-To: <17222.18470.744354.727641@gargle.gargle.HOWL>
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	 <17222.18470.744354.727641@gargle.gargle.HOWL>
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Hi,

   After some more toying around, I have seen that it works correctly
on ext2 fs but not
on etx3. :) ...

  My questions inline ..

On 10/7/05, Nikita Danilov <nikita@clusterfs.com> wrote:

> Blocks read by bread() and friends are cached in block device (not you
> :-) struct address_space. File data are cached in the per-inode struct
> address_space.

But even if I'm reading blocks from a device directly, they are
finally blocks from  the same inode. Why then are they stored
separately ?

> You are bypassing normal file sysetm caching and results can be
> unpredictable.

Is there then a safe way to do it w/o going through the filesystem caching ?

If not, I guess the following steps will be required :
a) Find out the page in the mapping corresponding to the blocks I need
to write.
b) Lock the page. Make changes. Mark it dirty and sync write it ?

Is there something in the kernel which does this already ?

Thanks for the help :) !

-Regards
 BD
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