RESEND: Inter-VM shared memory PCI device

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>

Makefile.target

@@ -190,6 +190,9 @@ obj-$(CONFIG_USB_OHCI) += usb-ohci.o
 obj-y += rtl8139.o
 obj-y += e1000.o
 
+# Inter-VM PCI shared memory
+obj-y += ivshmem.o
+
 # Hardware support
 obj-i386-y += vga.o
 obj-i386-y += mc146818rtc.o i8259.o pc.o

qemu-char.c

@@ -2087,6 +2087,12 @@ static void tcp_chr_read(void *opaque)
     }
 }
 
+CharDriverState *qemu_chr_open_eventfd(int eventfd){
+
+    return qemu_chr_open_fd(eventfd, eventfd);
+
+}
+
 static void tcp_chr_connect(void *opaque)
 {
     CharDriverState *chr = opaque;

qemu-char.h

@@ -94,6 +94,9 @@ void qemu_chr_info_print(Monitor *mon, const QObject *ret_data);
 void qemu_chr_info(Monitor *mon, QObject **ret_data);
 CharDriverState *qemu_chr_find(const char *name);
 
+/* add an eventfd to the qemu devices that are polled */
+CharDriverState *qemu_chr_open_eventfd(int eventfd);
+
 extern int term_escape_char;
 
 /* async I/O support */

qemu-doc.texi

@@ -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