linux-kernel - Re: [PATCH 5/7] FUSE: implement ioctl support

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Message-ID: <48B6EE36.5070209@kernel.org>
Date:	Thu, 28 Aug 2008 20:28:06 +0200
From:	Tejun Heo <tj@...nel.org>
To:	"H. Peter Anvin" <hpa@...nel.org>
CC:	fuse-devel@...ts.sourceforge.net, miklos@...redi.hu,
	greg@...ah.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/7] FUSE: implement ioctl support

H. Peter Anvin wrote:
> Tejun Heo wrote:
>> ioctl support is tricky to implement because only the ioctl
>> implementation itself knows which memory regions need to be read
>> and/or written.  To support this, fuse client can request retry of
>> ioctl specifying memory regions to read and write.  Deep copying
>> (nested pointers) can be implemented by retrying multiple times
>> resolving one depth of dereference at a time.
> 
> Okay, I'm going to say it... wouldn't it be better to have some kind of
> data structure description language which the userspace can register
> with the kernel to linearize the data on a per-ioctl basis (kind of like
> rpcgen)?

Ah.... funky.  If this retry thing is too repulsive, I guess the best
alternative would be directly accessing caller's memory as Miklos suggested.

Thanks.

-- 
tejun
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