ivshmem: Split ivshmem-plain, ivshmem-doorbell off ivshmem

ivshmem can be configured with and without interrupt capability
(a.k.a. "doorbell").  The two configurations have largely disjoint
options, which makes for a confusing (and badly checked) user
interface.  Moreover, the device can't tell the guest whether its
doorbell is enabled.

Create two new device models ivshmem-plain and ivshmem-doorbell, and
deprecate the old one.

Changes from ivshmem:

* PCI revision is 1 instead of 0.  The new revision is fully backwards
  compatible for guests.  Guests may elect to require at least
  revision 1 to make sure they're not exposed to the funny "no shared
  memory, yet" state.

* Property "role" replaced by "master".  role=master becomes
  master=on, role=peer becomes master=off.  Default is off instead of
  auto.

* Property "use64" is gone.  The new devices always have 64 bit BARs.

Changes from ivshmem to ivshmem-plain:

* The Interrupt Pin register in PCI config space is zero (does not use
  an interrupt pin) instead of one (uses INTA).

* Property "x-memdev" is renamed to "memdev".

* Properties "shm" and "size" are gone.  Use property "memdev"
  instead.

* Property "msi" is gone.  The new device can't have MSI-X capability.
  It can't interrupt anyway.

* Properties "ioeventfd" and "vectors" are gone.  They're meaningless
  without interrupts anyway.

Changes from ivshmem to ivshmem-doorbell:

* Property "msi" is gone.  The new device always has MSI-X capability.

* Property "ioeventfd" defaults to on instead of off.

* Property "size" is gone.  The new device can only map all the shared
  memory received from the server.

Guests can easily find out whether the device is configured for
interrupts by checking for MSI-X capability.

Note: some code added in sub-optimal places to make the diff easier to
review.  The next commit will move it to more sensible places.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1458066895-20632-37-git-send-email-armbru@redhat.com>

1 files changed, 18 insertions, 15 deletions

diff --git a/qemu-doc.texi b/qemu-doc.texi
index 8afbbcdfea..0dd01c78fd 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -1262,13 +1262,18 @@ basic example.
 
 @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
@@ -1282,8 +1287,7 @@ memory server is:
 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
 
@@ -1291,12 +1295,11 @@ When using the server, the guest will be assigned a VM ID (>=0) that allows gues
 using the same server to communicate via interrupts.  Guests can read their
 VM ID from a device register (see ivshmem-spec.txt).
 
-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.
+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.
 
 @subsubsection ivshmem and hugepages
 
@@ -1304,8 +1307,8 @@ Instead of specifying the <shm size> using POSIX shm, you may specify
 a memory backend that has hugepage support:
 
 @example
-qemu-system-i386 -object memory-backend-file,size=1G,mem-path=/dev/hugepages/my-shmem-file,share,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