Re: [ECOS] Possible fix for duplicated ARP entries in the FreeBSD stack

[Gary Thomas <gary@mlbassoc.com>]

On Fri, 2005-06-17 at 13:53 +0100, Nick Garnett wrote:
> Andrew Lunn <andrew@lunn.ch> writes:
> 
> > On Fri, Jun 17, 2005 at 12:57:49PM +0200, Sturle Mastberg wrote:
> > > Gary Thomas wrote:
> > > >On Fri, 2005-06-17 at 10:52 +0200, Sturle Mastberg wrote:
> > > >
> > > >>Hello,
> > > >>
> > > >>For some time I've had problem with duplicated ARP entries that have 
> > > >>caused all sorts of problems. I searched the archive and discovered that 
> > > >>the problem had been reported before:
> > > >>
> > > >>
> > > >>http://sourceware.org/ml/ecos-discuss/2004-11/msg00097.html
> > > >>
> > > >>
> > > >>My proposal to a fix is to make the sockaddr_inarp struct 
> > > >>(include/netinet/if_ether.h) equal in size to the sockaddr struct by 
> > > >>padding it at the end. This is exactly what is done to the sockaddr_in 
> > > >>struct (include/netinet/in.h) for different reasons.
> > > >>
> > > >>
> > > >>I reached this conclusion after I discovered that two virutally 
> > > >>identical calls to rtalloc1 (net/route.c) returned different results. 
> > > >>The first instance appears in arplookup (netinet/if_ether.c) where the 
> > > >>first parameter to rtalloc1 is a struct sockaddr_inarp cast to a struct 
> > > >>sockaddr. The second instance appears in ip_output (netinet/ip_output) 
> > > >>via rtalloc_ign (net/route.c) where the first parameter to rtalloc1 is 
> > > >>an actual struct sockaddr. The rtalloc1 function does a radix tree 
> > > >>search with a call to the rn_match function (net/radix.c). A closer look 
> > > >>at this code reveals that it does indeed depend on the size of the 
> > > >>supplied struct.
> > > >>
> > > >>
> > > >>The only conclusion a can draw from this is that the three structs: 
> > > >>sockaddr, sockaddr_in and sockaddr_inarp must all be of equal size. I 
> > > >>have checked the FreeBSD source repository that this is the case for the 
> > > >>original code.
> > > >>
> > > >>
> > > >>While browsing the FreeBSD source repository I discovered that the 
> > > >>sa_data character array member of the sockaddr struct was increased in 
> > > >>size in the eCos FreeBSD stack. Does anyone know why this increase was 
> > > >>introduced in eCos?
> > 
> > I beleave Nick did this for IPv6. This bigger size allows an IPv6
> > address to be placed into a sockaddr which you cannot normally do.
> 
> I thought that initially and had a look. The change I made was to
> struct sockaddr_in to make it match the increased sockaddr size so
> that some punned data structures would match. I think the change to
> struct sockaddr was done by Gary during the initial port to make IPv6
> addresses fit correctly. I'm sure it all has something to do with the
> lack of user/kernel space and the fact that we don't copy things to
> and fro as much as the BSD kernel does.

This is as I remember it as well.  Note the comment in the structure
(which I did not add or change) that bodes of this inconsistency.

Of course, if someone has a better way to handle it, feel free to
post a patch :-)

-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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