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

On Tue, May 20, 2014 at 11:17:32AM +0200, Martin Kletzander wrote: > 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. >> I came back to this mail right now because I need to have this implemented. Is there any progress on your side with this or should I try hitting this?

[...] >> 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. > @Cam (Cc'd) I was wondering about the role= options, so I looked into the code. It looks like role=peer just effectively disables migration. Did I miss any other difference? From the libvirt's POV I'd have a few more questions if I may. How does the migration work (if there's role=master) WRT other guests using the same shm? I found no shm_unlink call in QEMU sources (but again, I'm not experienced in QEMU's internals), does that mean that cleanup should be done by libvirt? Thank you for any info provided. Martin