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Re: [Xen-devel] Upstream QEMU based stubdom and rump kernel

On Tue, Mar 17, 2015 at 02:29:07PM +0000, Wei Liu wrote:
> I've now successfully built QEMU upstream with rump kernel. However to
> make it fully functional as a stubdom, there are some missing pieces to
> be added in.
> 1. The ability to access QMP socket (a unix socket) from Dom0. That
>    will be used to issue command to QEMU.

The QMP "socket" does not needs to be a unix socket. It can be any of
those (from qemu --help):
Character device options:
-chardev null,id=id[,mux=on|off]
         [,server][,nowait][,telnet][,reconnect=seconds][,mux=on|off] (tcp)
-chardev udp,id=id[,host=host],port=port[,localaddr=localaddr]
-chardev msmouse,id=id[,mux=on|off]
-chardev vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]]
-chardev ringbuf,id=id[,size=size]
-chardev file,id=id,path=path[,mux=on|off]
-chardev pipe,id=id,path=path[,mux=on|off]
-chardev pty,id=id[,mux=on|off]
-chardev stdio,id=id[,mux=on|off][,signal=on|off]
-chardev serial,id=id,path=path[,mux=on|off]
-chardev tty,id=id,path=path[,mux=on|off]
-chardev parallel,id=id,path=path[,mux=on|off]
-chardev parport,id=id,path=path[,mux=on|off]
-chardev spicevmc,id=id,name=name[,debug=debug]
-chardev spiceport,id=id,name=name[,debug=debug]

> 2. The ability to access files in Dom0. That will be used to write to /
>    read from QEMU state file.

To save a QEMU state (write), we do use a filename. But I guest we could
expand the QMP command (xen-save-devices-state) to use something else, if
it's easier.

To restore, we provide a file descriptor from libxl to QEMU, with the fd on
the file that contain the state we want to restore. But there are a few
other way to load a state (from qemu.git/docs/migration.txt):
- tcp migration: do the migration using tcp sockets
- unix migration: do the migration using unix sockets
- exec migration: do the migration using the stdin/stdout through a process.
- fd migration: do the migration using an file descriptor that is
  passed to QEMU.  QEMU doesn't care how this file descriptor is opened.

Anthony PERARD

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