linux-kernel - Re: [PATCH] hostfs: Use noop

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Date:	Wed, 14 Jan 2015 09:43:53 +0100
From:	Richard Weinberger <richard@....at>
To:	Christoph Hellwig <hch@...radead.org>
CC:	user-mode-linux-devel@...ts.sourceforge.net, dxld@...kboxed.org,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] hostfs: Use noop_fsync for directories

Am 14.01.2015 um 09:39 schrieb Christoph Hellwig:
> On Tue, Jan 13, 2015 at 11:26:38PM +0100, Richard Weinberger wrote:
>> hostfs tries do reduce the amount of syscall between guest and host as much
>> as possible. For file operations it passes everything down to the host but
>> for directory operations only ->iterate() does.
>>
>> It is already horrible slow, if we add an ->open() for directory too it would
>> get even more slower. :-(
> 
> This sounds fairlt dangerous.  At least add some good documentation
> explaining these semantics.

Understood. Maybe it is time to rebenchmark hostfs with full directory pass-through support.
Daniel, are you interested in a small kernel project?
As explained on IRC adding real support for directory fsync() should be an easy task.
The only interesting point is how much overhead it will add.

Thanks,
//richard
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