Re: [libvirt] [RFC] require for suggestions on support for ivshmem device

On Wed, May 14, 2014 at 08:23:21AM +0000, Wangrui (K) wrote: >Hi, > >Libvirt does not support ivshmem(Inter-VM Shared Memory) device recently, >thus, I would like to know if there's any plan to support it in the future? >If not, I would like to contribute a serial of patches to do so. >

>There are two ways to use ivshmem with qemu >(please refer to http://qemu.weilnetz.de/qemu-doc.html#pcsys_005fother_005fdevs ): >1.Guests map a POSIX shared memory region into the guest as a PCI device >that enables zero-copy communication to the application level of the guests, The basic syntax is: > > qemu-system-i386-device ivshmem, size = <size in format accepted by -m> [, shm = <shm name>] > >2.If desired, interrupts can be sent between guest VMs accessing the same shared memory region. >Interrupt support requires using a shared memory server and using a chardev socket to connect to it. >An example syntax when using the shared memory server is: > > qemu-system-i386-device ivshmem, size = <size in format accepted by -m> [, chardev = <id>] [, msi = on] > [, ioeventfd = on] [, vectors = n] [, role = peer | master] > qemu-system-i386-chardev socket, path = <path>, id = <id> > >The respective xml configuration for the above 2 qemu command lines are shown as below: > >Example1: automatically attach device with KVM > > <devices> > <ivshmem role='master'> > <memory name='dom-ivshmem' size='2'/> > </ivshmem> > </devices> > >NOTE: "size" means ivshmem size in unit MB, "name" means shm name > "role" is optional, it may be set to "master" or "peer", the default one is "master" > What do these roles mean, I mean what's the difference between master and peer and why is it only used with the chardev? Does it mean master can only send interrupts or...? Just curious.