Re: [libvirt] [PATCH] RFC: Introduce new domain create APIs to pass pre-opened FDs to LXC

On Tue, Jul 09, 2013 at 05:15:55PM +0100, Daniel P. Berrange wrote: > From: "Daniel P. Berrange" <berrange(a)redhat.com&gt; > > With container based virt, it is useful to be able to pass > pre-opened file descriptors to the container init process. > This allows for containers to be auto-activated from incoming > socket connections, passing the active socket into the container. > > To do this, introduce a pair of new APIs, virDomainCreateXMLWithFiles > and virDomainCreateWithFiles, which accept an array of file > descriptors. For the LXC driver, UNIX file descriptor passing > will be used to send them to libvirtd, which will them pass > them down to libvirt_lxc, which will then pass them to the container > init process. > > This will only be implemented for LXC right now, but the design > is generic enough it could work with other hypervisors, hence > I suggest adding this to libvirt.so, rather than libvirt-lxc.so No problem with the principle, but a bit confused by the arguments. > /** > + * virDomainCreateXMLWithFiles: > + * @conn: pointer to the hypervisor connection > + * @xmlDesc: string containing an XML description of the domain > + * @nfiles: number of file descriptors passed > + * @files: list of file descriptors passed > + * @flags: bitwise-OR of supported virDomainCreateFlags > + * > + * Launch a new guest domain, based on an XML description similar > + * to the one returned by virDomainGetXMLDesc() > + * This function may require privileged access to the hypervisor. > + * The domain is not persistent, so its definition will disappear when it > + * is destroyed, or if the host is restarted (see virDomainDefineXML() to > + * define persistent domains). > + * > + * @files provides an array of file descriptors which will be > + * made available to the 'init' process of the guest. This is > + * only supported for guests which use container based virtualization > + * technology. Hum, say you want to pas 4 fd, one for 0 stdin, one for 1 stdout one for 2 stderr, and somehow one for 4 a preopened fd, what would the files and nfiles contain ? 5 , [stdin, stdou, stderr, -1, fd4] ? basically is -1 used for holes in the list, shouldn't we instead pair (index for fd, fd) and provide an array of them ?