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Re: [Libvir] Remote patch, 2007/02/19



On Fri, Feb 23, 2007 at 10:37:32AM +0000, Richard W.M. Jones wrote:
> Daniel P. Berrange wrote:
> >On Wed, Feb 21, 2007 at 06:13:40PM +0000, Richard W.M. Jones wrote:
> >>Daniel P. Berrange wrote:
> >>
> >>>With that in mind I'd venture to suggest we ditch the whole idea of 
> >>>cookies
> >>>completely.
> >>>
> >>>Every method on the server end is already given a 
> >>>
> >>>    'struct svc_req *req'
> >>>
> >>>This struct contains a field
> >>>
> >>>    ' SVCXPRT *rq_xprt;'
> >>>
> >>>Which represents the data transport of the client. And the SVCXPRT struct
> >>>has as its first member the '  int xp_sock' which is the socket 
> >>>associated
> >>>with the client. 
> >>>
> >>>So we can trivially & securely map from a client's TCP connetion to the
> >>>virConnectPtr without needing any magic cookies.
> >>What concerns me here is that xp_sock is just a file descriptor and fds 
> >>can be reused.  It is also an fd that could be any of:
> >> * a TCPv6 socket
> >> * a TCPv4 socket
> >> * a Unix domain socket
> >> * on the client side, a socketpair (which on Linux is a funny type of 
> >>Unix domain socket)
> >>So finding something unique about it may be tricky.  What happens if two 
> >>clients connect in succession over the local Unix domain socket?
> >
> >I've just noticed that since we are providing our own server side transport
> >implementations in sunrpc/svc_{tcp,ext,gnutls}.c we already have a place
> >where we can safely put in cleanup hooks. In the 'svctcp_destroy' just
> >after we call 'xprt_unregister' we can call out to purge client state
> >associated with that FD. This ensures that we cleanup state before any new
> >connection can re-use the same FD number. So there's actually no need to 
> >replace the svc_run() method in this case after all.
> 
> I was hoping to avoid this.  Note that the contents of the sunrpc/ 
> subdirectory (the client and server transports) are independent of 
> libvirt and I hoped to publish them separately so they could be reused 
> in other places.  The other problem is the Unix transport, where we use 
> the transport from glibc directly. 

To keep them untied from libvirt one could allow a generic 'void (*cleanup)(void *)'
callback to be passed into the create methods for each transport, and simply
invoke that  from the descructor. We'd need to provide an alternate impl for
hte Unix transport too.

Dan.

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