[Qemu-devel] [PATCH v6 3/3] ivshmem: add check on protocol version in QEMU

[David Marchand]

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 <address@hidden>
---
 contrib/ivshmem-client/ivshmem-client.c |   13 ++++++++++---
 contrib/ivshmem-client/ivshmem-client.h |    1 +
 contrib/ivshmem-server/ivshmem-server.c |    9 +++++++++
 contrib/ivshmem-server/ivshmem-server.h |    1 +
 docs/specs/ivshmem_device_spec.txt      |    9 ++++++---
 hw/misc/ivshmem.c                       |   27 +++++++++++++++++++++++++--
 include/hw/misc/ivshmem.h               |   17 +++++++++++++++++
 7 files changed, 69 insertions(+), 8 deletions(-)
 create mode 100644 include/hw/misc/ivshmem.h

diff --git a/contrib/ivshmem-client/ivshmem-client.c 
b/contrib/ivshmem-client/ivshmem-client.c
index 11c805c..4413e26 100644
--- a/contrib/ivshmem-client/ivshmem-client.c
+++ b/contrib/ivshmem-client/ivshmem-client.c
@@ -201,10 +201,17 @@ ivshmem_client_connect(IvshmemClient *client)
         goto err_close;
     }
 
-    /* first, we expect our index + a fd == -1 */
+    /* first, we expect a protocol version */
+    if (ivshmem_client_read_one_msg(client, &tmp, &fd) < 0 ||
+        (tmp != IVSHMEM_PROTOCOL_VERSION) || fd != -1) {
+        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server\n");
+        goto err_close;
+    }
+
+    /* then, we expect our index + a fd == -1 */
     if (ivshmem_client_read_one_msg(client, &client->local.id, &fd) < 0 ||
         client->local.id < 0 || fd != -1) {
-        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server\n");
+        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server (2)\n");
         goto err_close;
     }
     IVSHMEM_CLIENT_DEBUG(client, "our_id=%ld\n", client->local.id);
@@ -216,7 +223,7 @@ ivshmem_client_connect(IvshmemClient *client)
         if (fd >= 0) {
             close(fd);
         }
-        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server (2)\n");
+        IVSHMEM_CLIENT_DEBUG(client, "cannot read from server (3)\n");
         goto err_close;
     }
     client->shm_fd = fd;
diff --git a/contrib/ivshmem-client/ivshmem-client.h 
b/contrib/ivshmem-client/ivshmem-client.h
index 284c4a3..9215f34 100644
--- a/contrib/ivshmem-client/ivshmem-client.h
+++ b/contrib/ivshmem-client/ivshmem-client.h
@@ -23,6 +23,7 @@
 #include <sys/select.h>
 
 #include "qemu/queue.h"
+#include "hw/misc/ivshmem.h"
 
 /**
  * Maximum number of notification vectors supported by the client
diff --git a/contrib/ivshmem-server/ivshmem-server.c 
b/contrib/ivshmem-server/ivshmem-server.c
index 91dc208..ea290f6 100644
--- a/contrib/ivshmem-server/ivshmem-server.c
+++ b/contrib/ivshmem-server/ivshmem-server.c
@@ -99,6 +99,15 @@ ivshmem_server_send_initial_info(IvshmemServer *server, 
IvshmemServerPeer *peer)
 {
     int ret;
 
+    /* send our protocol version first */
+    ret = ivshmem_server_send_one_msg(peer->sock_fd, IVSHMEM_PROTOCOL_VERSION,
+                                      -1);
+    if (ret < 0) {
+        IVSHMEM_SERVER_DEBUG(server, "cannot send version: %s\n",
+                             strerror(errno));
+        return -1;
+    }
+
     /* send the peer id to the client */
     ret = ivshmem_server_send_one_msg(peer->sock_fd, peer->id, -1);
     if (ret < 0) {
diff --git a/contrib/ivshmem-server/ivshmem-server.h 
b/contrib/ivshmem-server/ivshmem-server.h
index f85dcd2..38df7bb 100644
--- a/contrib/ivshmem-server/ivshmem-server.h
+++ b/contrib/ivshmem-server/ivshmem-server.h
@@ -30,6 +30,7 @@
 #include <sys/select.h>
 
 #include "qemu/queue.h"
+#include "hw/misc/ivshmem.h"
 
 /**
  * Maximum number of notification vectors supported by the server
diff --git a/docs/specs/ivshmem_device_spec.txt 
b/docs/specs/ivshmem_device_spec.txt
index 12f338e..3435116 100644
--- a/docs/specs/ivshmem_device_spec.txt
+++ b/docs/specs/ivshmem_device_spec.txt
@@ -64,6 +64,8 @@ It creates a shared memory object then waits for clients to 
connect on a unix
 socket.
 
 For each client (QEMU process) that connects to the server:
+- the server sends a protocol version, if client does not support it, the 
client
+  closes the communication,
 - the server assigns an ID for this client and sends this ID to him as the 
first
   message,
 - the server sends a fd to the shared memory object to this client,
@@ -86,9 +88,10 @@ been provided in qemu.git/contrib/ivshmem-client for debug.
 
 *QEMU as an ivshmem client*
 
-At initialisation, when creating the ivshmem device, QEMU gets its ID from the
-server then makes it available through BAR0 IVPosition register for the VM to
-use (see 'PCI device registers' subsection).
+At initialisation, when creating the ivshmem device, QEMU first receives a
+protocol version and closes communication with server if it does not match.
+Then, QEMU gets its ID from the server then makes it available through BAR0
+IVPosition register for the VM to use (see 'PCI device registers' subsection).
 QEMU then uses the fd to the shared memory to map it to BAR2.
 eventfds for all other clients received from the server are stored to implement
 BAR0 Doorbell register (see 'PCI device registers' subsection).
diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
index bd9d718..e08632b 100644
--- a/hw/misc/ivshmem.c
+++ b/hw/misc/ivshmem.c
@@ -26,6 +26,8 @@
 #include "qemu/event_notifier.h"
 #include "sysemu/char.h"
 
+#include "hw/misc/ivshmem.h"
+
 #include <sys/mman.h>
 #include <sys/types.h>
 
@@ -528,6 +530,27 @@ static void ivshmem_read(void *opaque, const uint8_t * 
buf, int flags)
     }
 }
 
+static void ivshmem_check_version(void *opaque, const uint8_t * buf, int flags)
+{
+    IVShmemState *s = opaque;
+    int tmp;
+    long version;
+
+    memcpy(&version, buf, sizeof(long));
+    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. */
@@ -742,8 +765,8 @@ static int pci_ivshmem_init(PCIDevice *dev)
 
         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;
diff --git a/include/hw/misc/ivshmem.h b/include/hw/misc/ivshmem.h
new file mode 100644
index 0000000..22c9f1f
--- /dev/null
+++ b/include/hw/misc/ivshmem.h
@@ -0,0 +1,17 @@
+/*
+ * Copyright 6WIND S.A., 2014
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or
+ * (at your option) any later version.  See the COPYING file in the
+ * top-level directory.
+ */
+
+#ifndef _IVSHMEM_H_
+#define _IVSHMEM_H_
+
+/**
+ * Protocol version
+ */
+#define IVSHMEM_PROTOCOL_VERSION 0x0
+
+#endif
-- 
1.7.10.4