File name of a base image (see @option{create} subcommand).
@item compat6
Create a VMDK version 6 image (instead of version 4)
+@item hwversion
+Specify vmdk virtual hardware version. Compat6 flag cannot be enabled
+if hwversion is specified.
@item subformat
Specifies which VMDK subformat to use. Valid options are
@code{monolithicSparse} (default),
@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:
+On Linux hosts, a shared memory device is available. The basic syntax
+is:
@example
-qemu-system-i386 -device ivshmem,size=@var{size},shm=@var{shm-name}
+qemu-system-x86_64 -device ivshmem-plain,memdev=@var{hostmem}
+@end example
+
+where @var{hostmem} names a host memory backend. For a POSIX shared
+memory backend, use something like
+
+@example
+-object memory-backend-file,size=1M,share,mem-path=/dev/shm/ivshmem,id=@var{hostmem}
@end example
If desired, interrupts can be sent between guest VMs accessing the same shared
ivshmem-server -p @var{pidfile} -S @var{path} -m @var{shm-name} -l @var{shm-size} -n @var{vectors}
# Then start your qemu instances with matching arguments
-qemu-system-i386 -device ivshmem,size=@var{shm-size},vectors=@var{vectors},chardev=@var{id}
- [,msi=on][,ioeventfd=on][,role=peer|master]
+qemu-system-x86_64 -device ivshmem-doorbell,vectors=@var{vectors},chardev=@var{id}
-chardev socket,path=@var{path},id=@var{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.
+VM ID from a device register (see ivshmem-spec.txt).
+
+@subsubsection Migration with ivshmem
+
+With device property @option{master=on}, the guest will copy the shared
+memory on migration to the destination host. With @option{master=off},
+the guest will not be able to migrate with the device attached. In the
+latter case, the device should be detached and then reattached after
+migration using the PCI hotplug support.
+
+At most one of the devices sharing the same memory can be master. The
+master must complete migration before you plug back the other devices.
@subsubsection ivshmem and hugepages
a memory backend that has hugepage support:
@example
-qemu-system-i386 -object memory-backend-file,size=1G,mem-path=/mnt/hugepages/my-shmem-file,id=mb1
- -device ivshmem,x-memdev=mb1
+qemu-system-x86_64 -object memory-backend-file,size=1G,mem-path=/dev/hugepages/my-shmem-file,share,id=mb1
+ -device ivshmem-plain,memdev=mb1
@end example
ivshmem-server also supports hugepages mount points with the
projects / qemu.git / blobdiff