linux-kernel - Re: [PATCH v4 1/2] init: add sys-wrapper.h

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Date:	Fri, 17 Sep 2010 14:40:24 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Namhyung Kim <namhyung@...il.com>
Cc:	Sam Ravnborg <sam@...nborg.org>, Arnd Bergmann <arnd@...db.de>,
	Phillip Lougher <phillip@...gher.demon.co.uk>,
	Al Viro <viro@...iv.linux.org.uk>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 1/2] init: add sys-wrapper.h

On Wed,  1 Sep 2010 00:30:18 +0900
Namhyung Kim <namhyung@...il.com> wrote:

> sys-wrapper.h contains wrapper functions for various syscalls used in init
> code. This wrappers handle proper address space conversion so that it can
> remove a lot of warnings from sparse.

This all looks pretty neat.

> +#define kernel_sys_call(call, ...)		\
> +({						\
> +	long result;				\
> +	mm_segment_t old_fs = get_fs();		\
> +	set_fs(KERNEL_DS);			\
> +	result = call(__VA_ARGS__);		\
> +	set_fs(old_fs);				\
> +	result;					\
> +})

I was worried that some syscalls don't need the set_fs(), and that this
would add overhead.  But I see that the patch addresses that.

> -	int err = sys_mount(name, "/root", fs, flags, data);
> +	int err = kernel_sys_mount(name, "/root", fs, flags, data);

It would be good if we could arrange for _all_ kernel syscalls to use
the wrappers.  ie: cause a direct call to sys_mount() to not compile?

I don't know how practical that would be.
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