Re: [Qemu-devel] [PATCH FYI 12/46] io: add QIOChannelTLS class

[Dr. David Alan Gilbert]

* Daniel P. Berrange (address@hidden) wrote:
> On Mon, Sep 07, 2015 at 04:31:08PM +0100, Dr. David Alan Gilbert wrote:
> > * Daniel P. Berrange (address@hidden) wrote:
> > > Add a QIOChannel subclass that can run the TLS protocol over
> > > the top of another QIOChannel instance. The object provides a
> > > simplified API to perform the handshake when starting the TLS
> > > session. The layering of TLS over the underlying channel does
> > > not have to be setup immediately. It is possible to take an
> > > existing QIOChannel that has done some handshake and then swap
> > > in the QIOChannelTLS layer. This allows for use with protocols
> > > which start TLS right away, and those which start plain text
> > > and then negotiate TLS.
> > > 
> > > Signed-off-by: Daniel P. Berrange <address@hidden>
> > 
> > > ---
> > > +#ifdef QIO_DEBUG
> > > +#define DPRINTF(fmt, ...) do { fprintf(stderr, fmt, ## __VA_ARGS__); } 
> > > while (0)
> > > +#else
> > > +#define DPRINTF(fmt, ...) do { } while (0)
> > > +#endif
> > 
> > Can you use the trace_ stuff rather than dprintf's; I've been trying
> > to remove them all from the migration code (and with trace configured in
> > stderr mode it works pretty easily).
> 
> Yeah, that's a good idea.
> 
> > On a different question; if this TLS channel is backed by a socket, can I do
> > a shutdown call that will bubble down to the socket?
> 
> The QIOChannel abstract base class did not define any shutdown method,
> since that's not a generally applicable concept - essentially only the
> sockets interface can do that. So I defined it as a method just on the
> QIOChannelSocket class. Given this, the QIOChannelTLS class does not
> know about the shutdown call.
> 
> This isn't a big deal though - the QIOChannelTLS struct exposes a
> pointer to the underling QIOChannel transport, so code that needs
> to do a shutdown, can get hold of the underlying channel and call
> shutdown on that.

You can imagine something like   compression->TLS->socket  and then it gets 
into the caller having to do a generic walk to figure out if it can
do it;  I'd rather not have to do that in caller.
I think I'd rather it was a facility on QIOChannel and then it gets
some type of ENOTSUPP error if it hits a layer that doesn't support it;
I guess the same might be true for socket behaviours like nagling and
maybe blocking.

> I forgot to do this properly when I integrated with the migration
> QEMUFile interface, so I'll fix that up, so shutdown works correctly
> with migration when TLS is enabled.

Dave

> 
> Regards,
> Daniel
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--
Dr. David Alan Gilbert / address@hidden / Manchester, UK