Re: [RFC v2 PATCH 1/3] init: add sys-wrapper.h

[Arnd Bergmann <arnd@arndb.de>]

On Sunday 29 August 2010, Namhyung Kim wrote:
> +
> +/* These macro are called just before/after actual syscalls. */
> +#define KSYS_PREPARE				\
> +	mm_segment_t old_fs = get_fs();		\
> +	set_fs(KERNEL_DS);
> +
> +#define KSYS_RESTORE				\
> +	set_fs(old_fs);

These macros are not that nice, because they depend on context.
I would probably open-code them in each function, or possibly
use a single macro to combine it to something like

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

static inline int kern_sys_link(const char *oldname, const char *newname)
{
	return kern_sys_call(sys_link, (const char __user __force *)oldname,
			     (const char __user __force *)newname);
}

> +static inline int kern_sys_fchown(unsigned int fd, uid_t user, gid_t group)
> +{
> +	int ret;
> +	KSYS_PREPARE;
> +
> +	ret = sys_fchown(fd, user, group);
> +
> +	KSYS_RESTORE;
> +	return ret;
> +}

When there are no pointer arguments, there is no need to do set_fs
tricks.

	Arnd