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The current I/O code for LXC uses a hand crafted event loop to forward I/O between the container & host app, based on epoll to handle EOF on PTYs. This event loop is not easily extensible to add more consoles, or monitor other types of file descriptors. Remove the custom event loop and replace it with a normal libvirt event loop. When detecting EOF on a PTY, disable the event watch on that FD, and fork off a background thread that does a edge-triggered epoll() on the FD. When the FD finally shows new incoming data, the thread re-enables the watch on the FD and exits. When getting EOF from a read() on the PTY, the existing code would do waitpid(WNOHANG) to see if the container had exited. Unfortunately there is a race condition, because even though the process has closed its stdio handles, it might still exist. To deal with this the new event loop uses a SIG_CHILD handler to perform the waitpid only when the container is known to have actually exited. * src/lxc/lxc_controller.c: Rewrite the event loop to use the standard APIs.
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>