Re: Possible SCTP peer receive window bug

["Frank Ch. Eigler" <fche@redhat.com>]

Hi -

Jamie.Parsons (@UNKNOWN_DOMAIN :-() wrote:

> [...] There is still a bug in the system tap script as the exit
> value of functions is always returned as the same as the entry value
> to functions.  [...]

This is an occasionally confusing aspect of systemtap .return probes.
As per the stapprobes man page and elsewhere, most $context variables
accessed from .return probes represent function *entry-time snapshots*.

Try instead use of the @entry() construct, which makes explicit
which values you wish to be entry-time evaluated, and which later.

probe module("sctp").function("sctp_process_init").return {
     printf("sctp_process_init updates assoc %p peer rwnd to %d\n", 
     @entry($asoc), 
     @cast(@entry($asoc),"sctp_association")->peer->rwnd);
     /* evaluated at .return time:          ^^^^^^^^^^^^ */
}

(http://sourceware.org/PR14437 should make the @cast unnecessary
eventually.)

- FChE