reintroduce handling of NULL route in ip_output()

Luigi Rizzo · *nix forums addict Joined: 07 Apr 2002 Posts: 72

[discussion on -arch, Bcc to -net in case someone is interested there]

Hi,
I would like to reintroduce the ability to pass a NULL
route to p_output(), which has been possible up to rev.1.34 of
ip_output().

Making ip_output() unable to handle NULL routes only saved a single
"if (ro == NULL)" check, but caused the work of allocating/deallocating
the route to be replicated in multiple places in the clients of
ip_output(), and the way this is done is very inconsistent, sometimes
involving the use of static variables which (apart from potential
errors due to misuse) are a no-no if we ever want to go to fine-grained
locking in the network stack. See for example how the route to
ip_output is passed in

netinet/igmp.c
netinet/ip_mroute.c
netinet/ip_input.c
netinet/tcp_subr.c

at least in one place there is a "bug" (like resetting some fields
of an automatic variable right before exiting from the block).
Other usages look suspicious too.

My reason to re-allow NULL routes in ip_output() are:

* simplify the code in the callers by centralizing a common
function;
* make another step towards the removal of global variables in the
protocol stack;

Does any of you have strong and _motivated_ objections ?

thanks
luigi

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