Re: [PATCHv2 net-next 3/5] sctp: add SCTP_EXPOSE_POTENTIALLY_FAILED_STATE sockopt

[Xin Long <lucien.xin@gmail.com>]

On Thu, Oct 10, 2019 at 8:40 PM Neil Horman <nhorman@tuxdriver.com> wrote:
>
> On Thu, Oct 10, 2019 at 05:28:34PM +0800, Xin Long wrote:
> > On Thu, Oct 10, 2019 at 12:18 AM Neil Horman <nhorman@tuxdriver.com> wrote:
> > >
> > > On Tue, Oct 08, 2019 at 11:28:32PM +0800, Xin Long wrote:
> > > > On Tue, Oct 8, 2019 at 9:02 PM David Laight <David.Laight@aculab.com> wrote:
> > > > >
> > > > > From: Xin Long
> > > > > > Sent: 08 October 2019 12:25
> > > > > >
> > > > > > This is a sockopt defined in section 7.3 of rfc7829: "Exposing
> > > > > > the Potentially Failed Path State", by which users can change
> > > > > > pf_expose per sock and asoc.
> > > > >
> > > > > If I read these patches correctly the default for this sockopt in 'enabled'.
> > > > > Doesn't this mean that old application binaries will receive notifications
> > > > > that they aren't expecting?
> > > > >
> > > > > I'd have thought that applications would be required to enable it.
> > > > If we do that, sctp_getsockopt_peer_addr_info() in patch 2/5 breaks.
> > > >
> > > I don't think we can safely do either of these things.  Older
> > > applications still need to behave as they did prior to the introduction
> > > of this notification, and we shouldn't allow unexpected notifications to
> > > be sent.
> > >
> > > What if you added a check in get_peer_addr_info to only return -EACCESS
> > > if pf_expose is 0 and the application isn't subscribed to the PF event?
> > We can't subscribe to PF event only, but all the SCTP_PEER_ADDR_CHANGE
> > events.
> >
> > Now I'm thinking both PF event and "return -EACCES" in get_peer_addr_info
> > are new, we should give 'expose' a default value that would disable both.
> > How do think if we set 'pf_expose = -1' by default. We send the pf event
> > only if (asoc->pf_expose > 0) in sctp_assoc_control_transport().
> >
> And if pf_expose = 0, we send the event, and return -EACCESS if we call
> the socket option and find a PF assoc?  If so, yes, I think that makes
> sense.
pf_expose:
-1: compatible with old application (by default)
0: not expose PF to user
1: expose PF to user

So it should be:
if pf_expose == -1:  not send event, not return -EACCESS
if pf_expose == 0: not send event, return -EACCESS
if pf_expose > 0: sent event, not return -EACCESS

makes sense?

>
> Neil
>
> > >
> > > Neil
> > >
> > > > >
> > > > >         David
> > > > >
> > > > > -
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> > > > >
> > > >
> >