Date: Thu, 29 May 2014 07:42:43 +0400 From: Gleb Smirnoff <glebius@FreeBSD.org> To: Julian Elischer <julian@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: <20140529034243.GR50679@FreeBSD.org> In-Reply-To: <538603A3.7080303@freebsd.org> References: <201405281315.s4SDFEvc061176@svn.freebsd.org> <5385EED0.1010506@freebsd.org> <20140528145619.GM50679@FreeBSD.org> <538603A3.7080303@freebsd.org>
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On Wed, May 28, 2014 at 11:41:23PM +0800, Julian Elischer wrote: J> On 5/28/14, 10:56 PM, Gleb Smirnoff wrote: J> > On Wed, May 28, 2014 at 10:12:32PM +0800, Julian Elischer wrote: J> > J> On 5/28/14, 9:15 PM, Gleb Smirnoff wrote: J> > J> > Author: glebius J> > J> > Date: Wed May 28 13:15:14 2014 J> > J> > New Revision: 266806 J> > J> > URL: http://svnweb.freebsd.org/changeset/base/266806 J> > J> > J> > J> > Log: J> > J> > Use M_WAITOK for the NGM_PIPE_SET_CFG control message. We expect it to J> > J> > arrive from userland only. J> > J> > J> > J> > Submitted by: Dmitry Luhtionov <dmitryluhtionov gmail.com> J> > J> what's to stop another node from generating it and sending it on? J> > J> generally a message may come from anywhere. J> > J> Just becasue YOU don't have module that J> > J> sends messages to ng_pipe, doesn't mean there never will be.. J> > J> also there are cases when the locking may force a message to be J> > J> delivered asynchronously. J> > J> > I know that. After resolving many issues with netgraph, I feel that J> > our policy should be towards putting some invariants on what events J> > SHOULD come from userland only and which events SHOULD be serviced J> > without memory failures. J> > J> > Current paradigma that messages are fully symmetrical and can come J> > from anywhere are quite a curious thought experiment. I liked that J> > for a long time. But in practice if we want to build a robust software J> > we should make more strict rules of using it. J> > J> > You could disagree, but if you try to fix this particular one liner J> > in the paradigma of "messages come from anywhere", then you will end J> > up with smth like 20 lines of code to this particular module. Next J> > comes the need to fix any software or script that sends NGM_PIPE_SET_CFG, J> > it now should be taught of dealing with ENOMEM. So, instead of one J> > liner you will bury yourself under tons of work. J> > J> > J> Then I suggest that we increment the protocol, and add support to messages J> to say whether they come from user space. J> and some providers only accept such messages. J> J> I have lost track of the code so I don't know if my comment about J> messages getting queued instead of delivered is still true. J> However if it is, then a message could be delivered by a kernel agent J> even J> if it is initiated by a userspace program. I don't think we need to increment protocol. Does it change? Right now we have a de facto standard, that some messages are expected from userland only. It is not enforced, it is just a habit. We should just keep this direction. -- Totus tuus, Glebius.
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