Date: Wed, 28 May 2014 23:41:23 +0800 From: Julian Elischer <julian@freebsd.org> To: Gleb Smirnoff <glebius@FreeBSD.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org, dmitryluhtionov@gmail.com Subject: Re: svn commit: r266806 - head/sys/netgraph Message-ID: <538603A3.7080303@freebsd.org> In-Reply-To: <20140528145619.GM50679@FreeBSD.org> References: <201405281315.s4SDFEvc061176@svn.freebsd.org> <5385EED0.1010506@freebsd.org> <20140528145619.GM50679@FreeBSD.org>
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On 5/28/14, 10:56 PM, Gleb Smirnoff wrote: > On Wed, May 28, 2014 at 10:12:32PM +0800, Julian Elischer wrote: > J> On 5/28/14, 9:15 PM, Gleb Smirnoff wrote: > J> > Author: glebius > J> > Date: Wed May 28 13:15:14 2014 > J> > New Revision: 266806 > J> > URL: http://svnweb.freebsd.org/changeset/base/266806 > J> > > J> > Log: > J> > Use M_WAITOK for the NGM_PIPE_SET_CFG control message. We expect it to > J> > arrive from userland only. > J> > > J> > Submitted by: Dmitry Luhtionov <dmitryluhtionov gmail.com> > J> what's to stop another node from generating it and sending it on? > J> generally a message may come from anywhere. > J> Just becasue YOU don't have module that > J> sends messages to ng_pipe, doesn't mean there never will be.. > J> also there are cases when the locking may force a message to be > J> delivered asynchronously. > > I know that. After resolving many issues with netgraph, I feel that > our policy should be towards putting some invariants on what events > SHOULD come from userland only and which events SHOULD be serviced > without memory failures. > > Current paradigma that messages are fully symmetrical and can come > from anywhere are quite a curious thought experiment. I liked that > for a long time. But in practice if we want to build a robust software > we should make more strict rules of using it. > > You could disagree, but if you try to fix this particular one liner > in the paradigma of "messages come from anywhere", then you will end > up with smth like 20 lines of code to this particular module. Next > comes the need to fix any software or script that sends NGM_PIPE_SET_CFG, > it now should be taught of dealing with ENOMEM. So, instead of one > liner you will bury yourself under tons of work. > > Then I suggest that we increment the protocol, and add support to messages to say whether they come from user space. and some providers only accept such messages. I have lost track of the code so I don't know if my comment about messages getting queued instead of delivered is still true. However if it is, then a message could be delivered by a kernel agent even if it is initiated by a userspace program.
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