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Message-ID: <AE90C24D6B3A694183C094C60CF0A2F6026B70E4@saturn3.aculab.com> Date: Fri, 7 Dec 2012 10:38:37 -0000 From: "David Laight" <David.Laight@...LAB.COM> To: "Thomas Graf" <tgraf@...g.ch>, "Nicolas Dichtel" <nicolas.dichtel@...nd.com> Cc: "David Miller" <davem@...emloft.net>, <netdev@...r.kernel.org> Subject: RE: [PATCH net-next 0/7] Allow to monitor multicast cache event via rtnetlink > On 12/06/12 at 09:43am, Nicolas Dichtel wrote: > > Le 05/12/2012 18:54, David Miller a écrit : > > >From: "David Laight" <David.Laight@...LAB.COM> > > >Date: Wed, 5 Dec 2012 11:41:33 -0000 > > > > > >>Probably worth commenting that the 64bit items might only be 32bit aligned. > > >>Just to stop anyone trying to read/write them with pointer casts. > > > > > >Rather, let's not create this situation at all. > > > > > >It's totally inappropriate to have special code to handle every single > > >time we want to put 64-bit values into netlink messages. > > > > > >We need a real solution to this issue. > > > > > The easiest way is to update *_ALIGNTO values (maybe we can keep > > NLMSG_ALIGNTO to 4). But I think that many userland apps have these > > values hardcoded and, the most important thing, this may increase > > size of many netlink messages. Hence we need probably to find > > something better. > > We can't do this, as you say, ALIGNTO is compiled into all the > binaries. > > A simple backwards compatible workaround would be to include an > unknown, empty padding attribute if needed. That would be 4 bytes > in size and could be used to include padding as needed. What are you going to align the data with respect to? I doubt you can assume that the start of the netlink message itself is 8 byte aligned - so any attempt to 8 byte align an item is probably doomed to failure. David -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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