On 11/07/2016 11:04 AM, Jonathan T. Leighton wrote:
Hi David -
Thanks for the response.
On 11/7/16 5:11 AM, David Laight wrote:
From: Jonathan T. Leighton
Sent: 05 November 2016 15:15
I've run into some behavior of getaddrinfo() that I think may be
incorrect. When getaddrinfo() is called with a numeric service argument
(as opposed to a name), it returns a list of addrinfo structures for
each protocol that it knows about, without referencing the
/etc/services
database. After installing lksctp I expected this list to include
IPPROTO_SCTP, but it doesn't. It looks to me like getaddrinfo() is
actually only returning addrinfo structures for all the protocols that
is knew about when it was built. Is this the correct behavior? Does
glibc need to be rebuilt after installing lksctp? Thanks for any help.
What you don't want is programs being given SCTP addresses when they
don't really want them.
I'm not sure I agree with this. getaddrinfo() can return addrinfo
structures with IPPROTO_UDP and IPPROTO_IP (in addition to
IPPROTO_TCP) - assuming that every returned addrinfo structure uses
IPPROTO_TCP is a problem. Code needs to be able to select among the
returned addrinfo structures appropriately, and including IPPROTO_SCTP
shouldn't break such code.
I've seen problems in the past (not Linux) where programs have tried
to use addresses on all available protocols when they really just meant
TCP or UDP.
IMO this is just bad coding.
I think I need to revise my opinion somewhat here. I've been advised
that there is significant code which assumes that protocol 0 and type
SOCK_STREAM means TCP. The workaround for getaddrinfo() is to include
IPPROTO_SCTP in the hints when using SCTP, and that works fine for me.
Thanks again for your input David.
- Jon
I don't think any of the address lookup functions are service specific,
AA and AAAA records probably aren't even protocol specific (below IP).
So programs that want to use SCTP can lookup TCP and then substitute
SCTP
when they create the socket.
Sure, but this is a hack. On a system with SCTP installed, SCTP
shouldn't be treated like a second class citizen.
Looking at the getaddrinfo() source shows that it's written to return
addrinfo structures with IPPROTO_SCTP, but only if it is built on a
system with SCTP installed. That suggests to me that installing lksctp
should include replacing glibc with a version that was built with SCTP
enabled.
- Jon
David
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