linux-kernel - Re: [PATCH v2 00/36] remove in-kernel syscall invocations (part 1)

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Message-ID: <20180316102506.GA769@light.dominikbrodowski.net>
Date:   Fri, 16 Mar 2018 11:25:06 +0100
From:   Dominik Brodowski <linux@...inikbrodowski.net>
To:     "Zhang, Ning A" <ning.a.zhang@...el.com>
Cc:     "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
        "mingo@...nel.org" <mingo@...nel.org>,
        "luto@...nel.org" <luto@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "arnd@...db.de" <arnd@...db.de>
Subject: Re: [PATCH v2 00/36] remove in-kernel syscall invocations (part 1)

On Fri, Mar 16, 2018 at 09:01:11AM +0000, Zhang, Ning A wrote:
> 在 2018-03-15四的 20:04 +0100，Dominik Brodowski写道：
> > Here is a re-spin of the first set of patches which reduce the number of
> > syscall invocations from within the kernel; the RFC may be found at
> > 
> > The rationale for this change is described in patch 1 as follows:
> > 
> > 	The syscall entry points to the kernel defined by SYSCALL_DEFINEx()
> > 	and COMPAT_SYSCALL_DEFINEx() should only be called from userspace
> > 	through kernel entry points, but not from the kernel itself. This
> > 	will allow cleanups and optimizations to the entry paths *and* to
> > 	the parts of the kernel code which currently need to pretend to be
> > 	userspace in order to make use of syscalls.
> 
> I think this is really bad to change syscalls one by one, to do_*
> 
> why not change SYSCALL_DEFINEx to define kernel wrappers?

Basically, for two reasons: First, only a subset of all syscalls require
such wrappers -- only about a third of all syscalls are called from within
the kernel at the moment (rough guess). Second, and more important: We want
to reduce the amount of such usage; see, e.g., the messages by Christoph and
Arnd in this thread.

Thanks,
	Dominik