Date: Fri, 16 Aug 2002 21:08:19 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Maxim Sobolev <sobomax@FreeBSD.ORG> Cc: hackers@FreeBSD.ORG, <net@FreeBSD.ORG> Subject: Re: Increasing size of if_flags field in the ifnet structure [patch for review] Message-ID: <20020816204055.N6621-100000@gamplex.bde.org> In-Reply-To: <3D5BF635.3764C796@FreeBSD.org>
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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. Bruce To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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