netdev - Re: [PATCH 1/7] CAN: Allocate protocol numbers for PF

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Message-ID: <ygf7im5h9r7.fsf@janus.isnogud.escape.de>
Date:	02 Oct 2007 16:27:40 +0200
From:	Urs Thuermann <urs@...ogud.escape.de>
To:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc:	netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
	Patrick McHardy <kaber@...sh.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oliver Hartkopp <oliver@...tkopp.net>,
	Oliver Hartkopp <oliver.hartkopp@...kswagen.de>
Subject: Re: [PATCH 1/7] CAN: Allocate protocol numbers for PF_CAN

Arnaldo Carvalho de Melo <acme@...stprotocols.net> writes:

> > --- net-2.6.24.orig/include/linux/if_arp.h	2007-10-02 12:10:51.000000000 +0200
> > +++ net-2.6.24/include/linux/if_arp.h	2007-10-02 12:11:01.000000000 +0200
> > @@ -52,6 +52,7 @@
> >  #define ARPHRD_ROSE	270
> >  #define ARPHRD_X25	271		/* CCITT X.25			*/
> >  #define ARPHRD_HWX25	272		/* Boards with X.25 in firmware	*/
> > +#define ARPHRD_CAN	280		/* Controller Area Network      */
> 
> Is 280 used in other OS? Just curious as why not using 273

When we first implemented PF_CAN a couple of years ago, we wanted to
avoid a clash with other ARPHRD_* defines which might be added, so we
skipped some numbers after the last used one.  I don't care what
number ARPHRD_CAN is, we can use 273.

> > --- net-2.6.24.orig/include/linux/socket.h	2007-10-02 12:10:51.000000000 +0200
> > +++ net-2.6.24/include/linux/socket.h	2007-10-02 12:11:01.000000000 +0200
> > @@ -185,6 +185,7 @@
> >  #define AF_PPPOX	24	/* PPPoX sockets		*/
> >  #define AF_WANPIPE	25	/* Wanpipe API Sockets */
> >  #define AF_LLC		26	/* Linux LLC			*/
> > +#define AF_CAN		29	/* Controller Area Network      */
> 
> Ditto
> 
> >  #define AF_TIPC		30	/* TIPC sockets			*/
> >  #define AF_BLUETOOTH	31	/* Bluetooth sockets 		*/
> >  #define AF_IUCV		32	/* IUCV sockets			*/

For the same reason as above, we didn't use 27, but the last unused
without modifying AF_MAX.  First, we had AF_CAN == 30, then TIPC used
that number and we changed AF_CAN to 29.  Changing again would mean an
ABI change and would break user apps.  If there is a pressing reason I
wouldn't mind personally, but it would probably upset quite a number
of users of our code.  It seems common now to allocate these numbers
from the top in decreasing order.

urs
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