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Date: Thu, 18 Jan 2018 17:10:20 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Christoph Hellwig <hch@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Network Development <netdev@vger.kernel.org>,
	Dan Williams <dan.j.williams@intel.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arch@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
	Kees Cook <keescook@chromium.org>,
	kernel-hardening@lists.openwall.com,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	the arch/x86 maintainers <x86@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Alan Cox <alan@linux.intel.com>, David Miller <davem@davemloft.net>
Subject: Re: [RFC][PATCH] get rid of the use of set_fs() (by way of
 kernel_recvmsg()) in sunrpc
Message-ID: <20180118171020.GA13338@ZenIV.linux.org.uk>
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On Thu, Jan 18, 2018 at 08:29:57AM -0800, Christoph Hellwig wrote:
> > 	We could turn ->msg_control/->msg_controllen into another
> > iov_iter, but seeing that we never do scatter-gather for those
> > IMO that would be a massive overkill.  A flag controlling whether
> > ->msg_control is kernel or userland pointer would do, especially
> > since we already have a flag for "do we want a native or compat
> > layout for cmsg" in there.
> 
> While your current hack seems like a nice short term improvement
> I think we need an iov_iter or iov_iter-light there in the long run.

For one caller in the entire history of the kernel?

> Same for ioctl so that we can pass properly typed kernel or user
> buffers through without all these set_fs hacks.

Umm...  Most of the PITA with ioctls is due to compat ones being
reformatted for native and fed under set_fs().  I actually have
a series dealing with most of such places for net ioctls.  Sure,
there's also ioctl_by_bdev(), but for those we might be better
off exposing the things like ->get_last_session() and its ilk to
filesystems that want to deal with cdroms...

It's kernel_setsockopt() that is the real PITA...