linux-kernel - Re: [SUGGESTION]: drop virtual merge accounting in I/O requests

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Date:	Tue, 15 Jul 2008 09:16:52 -0400 (EDT)
From:	Mikulas Patocka <mpatocka@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	davem@...emloft.net, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org, jens.axboe@...cle.com
Subject: Re: [SUGGESTION]: drop virtual merge accounting in I/O requests

On Tue, 15 Jul 2008, Andi Kleen wrote:

> Mikulas Patocka wrote:
>>>> BTW. what should the block device driver do when it receives a mapping
>>>> error? (if it aborts the request and it was write request, there will be
>>>> data corruption).
>>>
>>> I'm not sure how a aborted request can corrupt data on disk.
>>
>> Writes are done by an async daemon and no one checks for their
>> completion status. If there are three writes to directory, inode table
>> and inode bitmap and one of these writes fail, there's no code to undo
>> the other two. So the filesystem will be corrupted on write failure.
>
> Normally journaling in ordered mode takes care of that. The transaction
> is not committed until all earlier data has been successfully written.

And if there was write error, then what happens? Retry? Blocking of any 
further updates?

> And even the other fs typically turn the file system read only
> on IO error to prevent further corruption.

There is no interface how filesystem could query that buffer marked with 
mark_buffer_dirty was not written. Or is there?

Mikulas
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