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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 redhat com>
> 
> 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 ?

Daniel

-- 
Daniel Veillard      | Open Source and Standards, Red Hat
veillard redhat com  | libxml Gnome XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | virtualization library  http://libvirt.org/


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