Date: Fri, 16 Aug 2002 15:11:13 +0300 (EEST) From: Maxim Sobolev <max@vega.com> To: bde@zeta.org.au (Bruce Evans) Cc: sobomax@FreeBSD.ORG (Maxim Sobolev), hackers@FreeBSD.ORG, net@FreeBSD.ORG Subject: Re: Increasing size of if_flags field in the ifnet structure [patch Message-ID: <200208161211.g7GCBDrL005351@vega.vega.com> In-Reply-To: <20020816204055.N6621-100000@gamplex.bde.org> from "Bruce Evans" at ΑΧΗ 16, 2002
next in thread | previous in thread | raw e-mail | index | archive | help
> > On Thu, 15 Aug 2002, Maxim Sobolev wrote: > > > When implementing ability to switch interface into promisc mode using > > ifconfig(8) I've stumbled into the problem with already exhausted > > space in the `short if_flags' field in the ifnet structure. I need to > > allocate one new flag, while we already have 16 IFF_* flags, and even > > one additional flag which is implemented using currently free > > if_ipending field of the said structure. Attached patch is aimed at > > increasing size of if_flags to 32 bits, as well as to clean-up > > if_ipending abuse. Granted, it will break backward ABI compatibility, > > but IMO it is not a big problem. > > Why isn't it a bug problem? It affects an application ABI (most socket > ioctls). We have whole syscalls whose purpose is to avoid breaking > application ABIs back to about 4.3BSD. Some of them may even work. > > > Index: src/share/man/man4/netintro.4 > > =================================================================== > > RCS file: /home/ncvs/src/share/man/man4/netintro.4,v > > retrieving revision 1.20 > > diff -d -u -r1.20 netintro.4 > > --- src/share/man/man4/netintro.4 18 Mar 2002 12:39:32 -0000 1.20 > > +++ src/share/man/man4/netintro.4 15 Aug 2002 18:33:42 -0000 > > @@ -197,7 +197,7 @@ > > struct sockaddr ifru_addr; > > struct sockaddr ifru_dstaddr; > > struct sockaddr ifru_broadaddr; > > - short ifru_flags; > > + int ifru_flags; > > int ifru_metric; > > int ifru_mtu; > > int ifru_phys; > > This particular ABI seems to have been broken before (in if.h 1.50 on > 1999/02/09), since the actual struct has "short ifru_flags[2];" followed > by "short if_index;" instead of "short ifru_flags;", and it has 2 new > struct members at the end too. If the struct were actually as above, > then changing the short to an int would almost be binary compatible > since it would just expand ifru_flags to use the 2 bytes of unnamed > padding caused by the poor layout, so the struct wouldn't expand and > the other members wouldn't move. Enlarging ifru_flags itself might > only break big-endian machines (little-endian ones wouldn't notice > providing the padding is zeroed). > > > Index: src/share/man/man9/ifnet.9 > > Breaking kernel ABIs isn't so important. They should only be compatible > within major releases. BTW, I've just realised that we can easily avoid breaking application ABI by using currently unused ifr_ifru.ifru_flags[2] (aka. ifr_prevflags) for storing another 16 flags. What do people think? -Maxim To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200208161211.g7GCBDrL005351>