[dpdk-dev] [RFC] librte_vhost: Add unix domain socket fd registration

[Yuanhan Liu]

On Tue, Jun 21, 2016 at 09:15:03AM -0400, Aaron Conole wrote:
> Yuanhan Liu <yuanhan.liu at linux.intel.com> writes:
> 
> > On Fri, Jun 17, 2016 at 11:32:36AM -0400, Aaron Conole wrote:
> >> Prior to this commit, the only way to add a vhost-user socket to the
> >> system is by relying on librte_vhost to open the unix domain socket and
> >> add it to the unix socket list.  This is problematic for applications
> >> which would like to set the permissions,
> >
> > So, you want to address the issue raised by following patch?
> >
> >     http://dpdk.org/dev/patchwork/patch/12222/
> 
> That patch does try to address the issue, however - it has some
> problems.  The biggest is a TOCTTOU issue when using chown.  The way to
> solve that issue properly is different depending on which operating
> system is being used (for instance, FreeBSD doesn't honor
> fchown(),fchmod() on file descriptors).  My solution is basically to
> punt that responsibility to the controlling application.
> 
> > I would still like to stick to my proposal, that is to introduce a
> > new API to do the permission change at anytime, if we end up with
> > wanting to introduce a new API.
> 
> I've spent a lot of time looking at the TOCTTOU problem, and I think
> that is a really hard problem to solve portably.  Might be good to just
> start with the flexible mechanism here that lets the application
> developer satisfy their own needs.
> 
> >> or applications which are not
> >> directly allowed to open sockets due to policy restrictions.
> >
> > Could you name a specific example?
> 
> SELinux policy might require one application to open the socket, and
> pass it back via a dbus mechanism.  I can't actually think of a concrete
> implemented case, so it may not be valid.
> 
> > BTW, JFYI, since 16.07, DPDK supports client mode. It's QEMU (acting
> > as the server) will create the socket file. I guess that would diminish
> > (or even avoid?) the permission pain that DPDK acting as server brings.
> > I doubt the API to do the permission change is really needed then.
> 
> I wouldn't say it 'solves' the issue so much as hopes no one uses server
> mode in DPDK.  I agree, for OvS, it could.

Actually, I think I would (personally) suggest people to switch to DPDK
vhost-user client mode, for two good reasons:

- it should solve the socket permission issue raised by you and Christian.

- it has the "reconnect" feature since 16.07. Which means guest network
  will still work from a DPDK vhost-user restart/crash. DPDK vhost-user
  as server simply doesn't support that.

And FYI, Loftus is doing the DPDK for OVS intergration. Not quite sure
whether she put the client mode as the default mode though.

> Thanks so much for your thoughts and review on this, Yuanhan Liu!

Thank you for proposing ideas to make DPDK better!

	--yliu