Date: Fri, 28 Sep 2001 21:15:13 +0000 From: Vladimir Dozen <vladimir-dozen@mail.ru> To: Robert Watson <rwatson@FreeBSD.org> Cc: hackers@FreeBSD.org Subject: Re: calling open() from inside kernel Message-ID: <20010928211513.A294@eix.do-labs.spb.ru> In-Reply-To: <Pine.NEB.3.96L.1010928082423.31337D-100000@fledge.watson.org>; from rwatson@FreeBSD.org on Fri, Sep 28, 2001 at 08:29:10AM -0400 References: <20010927234624.A403@eix.do-labs.spb.ru> <Pine.NEB.3.96L.1010928082423.31337D-100000@fledge.watson.org>
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ehlo.
> Generally speaking, you don't want to invoke system call functionss from
> within the kernel due to address space expectations, you want to invoke
> the supporting service calls. Probably what that maps into in your case is
> using NDINIT()/namei() on a string in UIO_SYSSPACE, and then using
> vn_open(). You'll want to look carefully at the open() code to see if
> there are other things to do/watch out for.
That was exactly what I've done. The problem here is that each time
someone in kernel space will try to open a file, he/she has to
retype the same code already in vfs_syscalls.c. I would like
to see more general version of open and two short wrappers -- one
for userspace and one for kernel space, something like:
/* generic */
open_generic(struct proc* proc,struct open_args* oa,boolean_t inkernel)
{
if( inkernel ) NDINIT(...,UIO_SYSSPACE,...);
else NDINIT(...,UIO_USERSPACE,...);
...
}
/* user-space */
open(proc,oa){ return open_generic(proc,oa,0); }
/* kernel space */
open_sysspace(proc,oa){ return open_generic(proc,oa,1); }
Well, I see I was wanted too much.
> In the Linux emulation code, when the kernel wants to change arguments
> around and keep them in userspace, it uses space allocated out of the
> stack gap, a section of VM I assume is otherwise unused in userspace (and
> presumably is per-stack, or there would be problems with linux threading).
This cure is more dangerous than illness itself. ;)
--
dozen @ home
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