linux-ext4 - Re: [PATCH 2/2] ext2: Add blk_issue

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Message-ID: <20090114182706.GA24719@elf.ucw.cz>
Date:	Wed, 14 Jan 2009 19:27:06 +0100
From:	Pavel Machek <pavel@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] ext2: Add blk_issue_flush() to syncing paths

Hi!

> Also, the changelog needs some work, methinks.
> 
> /**
>  * blkdev_issue_flush - queue a flush
>  * @bdev:	blockdev to issue flush for
>  * @error_sector:	error sector
>  *
>  * Description:
>  *    Issue a flush for the block device in question. Caller can supply
>  *    room for storing the error offset in case of a flush error, if they
>  *    wish to.  Caller must run wait_for_completion() on its own.
>  */
> 
> So afaict the change you've made is incomplete.  We'll queue a
> writeback command to the disk but we won't wait for it to be sent down
> the wire.  Nor do we wait for the command to complete at the device
> end.  So it can still be a looong time (seconds!) before the data which
> the user thinks is on disk really is safe.
> 
> Yes?
> 
> If so, this design decision should be described in the changelog, and
> justified.  Actually, doing this in the comment over
> ext3_blkdev_issue_flush() would be good.

Actually, if sync() and fsync() do not work, it probably needs more
than a comment in changelog. Like comment in documentation, in big
bold letters.
									Pavel

-- 
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