motorhead/qemu
1
0
Fork 0
mirror of https://github.com/Motorhead1991/qemu.git synced 2025-08-07 09:43:56 -06:00
Code Issues Projects Releases Packages Wiki Activity Actions

RESEND: Inter-VM shared memory PCI device

Browse source 
resend for bug fix related to removal of irqfd

Support an inter-vm shared memory device that maps a shared-memory object as a
PCI device in the guest.  This patch also supports interrupts between guest by
communicating over a unix domain socket.  This patch applies to the qemu-kvm
repository.

    -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]

Interrupts are supported between multiple VMs by using a shared memory server
by using a chardev socket.

    -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
           [,chardev=<id>][,msi=on][,ioeventfd=on][,vectors=n][,role=peer|master]
    -chardev socket,path=<path>,id=<id>

The shared memory server, sample programs and init scripts are in a git repo here:

    www.gitorious.org/nahanni

Signed-off-by: Cam Macdonell <cam@cs.ualberta.ca>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Cam Macdonell 2010-07-27 10:54:13 -06:00 • committed by Anthony Liguori
parent 2431296806
commit 6cbf4c8c64
5 changed files with 883 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

43
qemu-doc.texi
View file

@ -706,6 +706,49 @@ Using the @option{-net socket} option, it is possible to make VLANs
that span several QEMU instances. See @ref{sec_invocation} to have a
basic example.
@section Other Devices
@subsection Inter-VM Shared Memory device
With KVM enabled on a Linux host, a shared memory device is available. 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:
@example
qemu -device ivshmem,size=<size in format accepted by -m>[,shm=<shm name>]
@end example
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. The code for the shared memory server
is qemu.git/contrib/ivshmem-server. An example syntax when using the shared
memory server is:
@example
qemu -device ivshmem,size=<size in format accepted by -m>[,chardev=<id>]
[,msi=on][,ioeventfd=on][,vectors=n][,role=peer|master]
qemu -chardev socket,path=<path>,id=<id>
@end example
When using the server, the guest will be assigned a VM ID (>=0) that allows guests
using the same server to communicate via interrupts. Guests can read their
VM ID from a device register (see example code). Since receiving the shared
memory region from the server is asynchronous, there is a (small) chance the
guest may boot before the shared memory is attached. To allow an application
to ensure shared memory is attached, the VM ID register will return -1 (an
invalid VM ID) until the memory is attached. Once the shared memory is
attached, the VM ID will return the guest's valid VM ID. With these semantics,
the guest application can check to ensure the shared memory is attached to the
guest before proceeding.
The @option{role} argument can be set to either master or peer and will affect
how the shared memory is migrated. With @option{role=master}, the guest will
copy the shared memory on migration to the destination host. With
@option{role=peer}, the guest will not be able to migrate with the device attached.
With the @option{peer} case, the device should be detached and then reattached
after migration using the PCI hotplug support.
@node direct_linux_boot
@section Direct Linux Boot