ivshmem: add check on protocol version in QEMU

Send a protocol version as the first message from server, clients must
close communication if they don't support this protocol version.  Older
QEMUs should be fine with this change in the protocol since they
overrides their own vm_id on reception of an id associated to no
eventfd.

Signed-off-by: David Marchand <david.marchand@6wind.com>
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
[use fifo_update_and_get()]
Reviewed-by: Claudio Fontana <claudio.fontana@huawei.com>

1 files changed, 29 insertions, 2 deletions

diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
index 0dd8da1..cf774ea 100644
--- a/hw/misc/ivshmem.c
+++ b/hw/misc/ivshmem.c
@@ -27,6 +27,8 @@
 #include "qemu/fifo8.h"
 #include "sysemu/char.h"
 
+#include "hw/misc/ivshmem.h"
+
 #include <sys/mman.h>
 #include <sys/types.h>
 #include <limits.h>
@@ -596,6 +598,31 @@ static void ivshmem_read(void *opaque, const uint8_t *buf, int size)
     }
 }
 
+static void ivshmem_check_version(void *opaque, const uint8_t * buf, int size)
+{
+    IVShmemState *s = opaque;
+    int tmp;
+    long version;
+
+    if (!fifo_update_and_get(s, buf, size,
+                             &version, sizeof(version))) {
+        return;
+    }
+
+    tmp = qemu_chr_fe_get_msgfd(s->server_chr);
+    if (tmp != -1 || version != IVSHMEM_PROTOCOL_VERSION) {
+        fprintf(stderr, "incompatible version, you are connecting to a ivshmem-"
+                "server using a different protocol please check your setup\n");
+        qemu_chr_delete(s->server_chr);
+        s->server_chr = NULL;
+        return;
+    }
+
+    IVSHMEM_DPRINTF("version check ok, switch to real chardev handler\n");
+    qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive, ivshmem_read,
+                          ivshmem_event, s);
+}
+
 /* Select the MSI-X vectors used by device.
  * ivshmem maps events to vectors statically, so
  * we just enable all vectors on init and after reset. */
@@ -769,8 +796,8 @@ static void pci_ivshmem_realize(PCIDevice *dev, Error **errp)
 
         s->eventfd_chr = g_malloc0(s->vectors * sizeof(CharDriverState *));
 
-        qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive, ivshmem_read,
-                     ivshmem_event, s);
+        qemu_chr_add_handlers(s->server_chr, ivshmem_can_receive,
+                              ivshmem_check_version, ivshmem_event, s);
     } else {
         /* just map the file immediately, we're not using a server */
         int fd;