Re: [Qemu-devel] [PATCH for-1.1?] slirp: Avoid redefining MAX_TCPOPTLEN

[Andreas Färber]

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Am 28.05.2012 13:40, schrieb Jan Kiszka:
> On 2012-05-27 14:02, Andreas Färber wrote:
>> MAX_TCPOPTLEN is being defined as 32. Darwin has it as 40,
>> causing a warning. The value is only used to declare an array,
>> into which currently 4 bytes are written at most. It should
>> therefore be acceptable to adopt the host's definition.
>> 
>> Therefore only define MAX_TCPOPTLEN if not already defined.
>> 
>> Signed-off-by: Andreas Färber <address@hidden> --- 
>> slirp/tcp_output.c |    2 ++ 1 files changed, 2 insertions(+), 0
>> deletions(-)
>> 
>> diff --git a/slirp/tcp_output.c b/slirp/tcp_output.c index
>> 779314b..9815123 100644 --- a/slirp/tcp_output.c +++
>> b/slirp/tcp_output.c @@ -47,7 +47,9 @@ static const u_char
>> tcp_outflags[TCP_NSTATES] = { };
>> 
>> 
>> +#ifndef MAX_TCPOPTLEN #define MAX_TCPOPTLEN 32      /* max # bytes
>> that go in options */ +#endif
>> 
>> /* * Tcp output routine: figure out what should be sent and send
>> it.
> 
> Let's be conservative for 1.1 and do #undef MAX_TCPOPTLEN instead.
> Does this work as well?

For Leopard I'd guess so.

What I had in mind here was that it was suggested earlier by one of
you to use host defines for 1.2 wherever possible, and this seemed
like low-hanging fruit. I do see Stefan's point though.

An alternative, host-overriding version would be:

#if !defined(MAX_TCPOPTLEN) || MAX_TCPOPTLEN < 4
#undef MAX_TCPOPTLEN
...
#endif

Stefan's point in turn means that defining MAX_TCPOPTLEN to something
larger than the host supports could in theory cause trouble when used
with host functions (which we currently don't seem to).

A safe host-adopting version would be:

#if defined(MAX_TCPOPTLEN) && MAX_TCPOPTLEN >= 4
#define SLIRP_MAX_TCPOPTLEN MAX_TCPOPTLEN
#else
#define SLIRP_MAX_TCPOPTLEN 32
#endif

and use opt[SLIRP_MAX_TCPOPTLEN]. In that case we could probably just
rename MAX_TCPOPTLEN -> SLIRP_MAX_TCPOPTLEN in the first place.

Yet another option would be to drop MAX_TCPOPTLEN and to hardcode the
actually used opt[4].

Which do you prefer? :-)

Andreas

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