From mboxrd@z Thu Jan  1 00:00:00 1970
From: ebiederm@xmission.com (Eric W. Biederman)
Subject: Re: fanotify as syscalls
Date: Mon, 21 Sep 2009 17:15:28 -0700
Message-ID: <m1r5tzq1gf.fsf@fess.ebiederm.org>
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Cc: Jamie Lokier <jamie@shareable.org>,
	Evgeniy Polyakov <zbr@ioremap.net>,
	Eric Paris <eparis@redhat.com>,
	David Miller <davem@davemloft.net>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	netdev@vger.kernel.org, viro@zeniv.linux.org.uk,
	alan@linux.intel.com, hch@infradead.org
To: Linus Torvalds <torvalds@linux-foundation.org>
Return-path: <linux-kernel-owner+glk-linux-kernel-3=40m.gmane.org-S1754707AbZIVAPm@vger.kernel.org>
In-Reply-To: <alpine.LFD.2.01.0909170934450.4950@localhost.localdomain> (Linus Torvalds's message of "Thu\, 17 Sep 2009 09\:40\:16 -0700 \(PDT\)")
Sender: linux-kernel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

Linus Torvalds <torvalds@linux-foundation.org> writes:

> Quite frankly, I have _never_ever_ seen a good reason for talking to the 
> kernel with some idiotic packet interface. It's just a fancy way to do 
> ioctl's, and everybody knows that ioctl's are bad and evil. Why are fancy 
> packet interfaces suddenly much better?

For working with the networking stack there are a lot of advantages because
netlink is the interface to everything in the network stack.

There are nice things like the packet to create a new interface is the same
packet the kernel sends everyone to report a new interface etc.

netlink also seems to get the structured data thing right.  You can
parse the packet even if you don't understand everything.  Each tag is
well defined like a syscall, taking exactly one kind of argument.
Which avoids the worst failure of ioctl in that you can't even parse
everything, and the argument may be a linked list in the calling
process or something else atrocious.

All of that said syscalls are good, and I would not recommend netlink
to anything not in the network stack.

Eric