[Xen-changelog] [qemu-xen staging] xen-bus: only set the xen device frontend state if it is missing

[patchbot@xxxxxxx]

commit 933ebad2470a169504799a1d95b8e410bd9847ef
Author:     Mark Syms <mark.syms@xxxxxxxxxx>
AuthorDate: Wed Sep 18 12:57:44 2019 +0100
Commit:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
CommitDate: Fri Sep 27 11:21:35 2019 +0100

    xen-bus: only set the xen device frontend state if it is missing
    
    Some toolstack implementations will set the frontend xenstore
    keys to Initialising which will then trigger the in guest PV
    drivers to begin initialising and some implementations will
    then set their state to Closing. If this has occurred then
    device realize must not overwrite the frontend keys as then
    the handshake will stall.
    
    Signed-off-by: Mark Syms <mark.syms@xxxxxxxxxx>
    
    Also avoid creating the frontend area if it already exists.
    
    Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
    Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    Message-Id: <20190918115745.39006-1-paul.durrant@xxxxxxxxxx>
    Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
    (cherry picked from commit 6bd6b955c0b2666263700d39db153ab43c5e0c9e)
---
 hw/xen/xen-bus.c | 47 +++++++++++++++++++++++++++++++----------------
 1 file changed, 31 insertions(+), 16 deletions(-)

diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c
index 32bbd2b541..63469e0cf9 100644
--- a/hw/xen/xen-bus.c
+++ b/hw/xen/xen-bus.c
@@ -857,6 +857,13 @@ static void xen_device_frontend_changed(void *opaque)
     }
 }
 
+static bool xen_device_frontend_exists(XenDevice *xendev)
+{
+    enum xenbus_state state;
+
+    return (xen_device_frontend_scanf(xendev, "state", "%u", &state) == 1);
+}
+
 static void xen_device_frontend_create(XenDevice *xendev, Error **errp)
 {
     XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev)));
@@ -865,19 +872,25 @@ static void xen_device_frontend_create(XenDevice *xendev, 
Error **errp)
 
     xendev->frontend_path = xen_device_get_frontend_path(xendev);
 
-    perms[0].id = xendev->frontend_id;
-    perms[0].perms = XS_PERM_NONE;
-    perms[1].id = xenbus->backend_id;
-    perms[1].perms = XS_PERM_READ | XS_PERM_WRITE;
+    /*
+     * The frontend area may have already been created by a legacy
+     * toolstack.
+     */
+    if (!xen_device_frontend_exists(xendev)) {
+        perms[0].id = xendev->frontend_id;
+        perms[0].perms = XS_PERM_NONE;
+        perms[1].id = xenbus->backend_id;
+        perms[1].perms = XS_PERM_READ | XS_PERM_WRITE;
 
-    g_assert(xenbus->xsh);
+        g_assert(xenbus->xsh);
 
-    xs_node_create(xenbus->xsh, XBT_NULL, xendev->frontend_path, perms,
-                   ARRAY_SIZE(perms), &local_err);
-    if (local_err) {
-        error_propagate_prepend(errp, local_err,
-                                "failed to create frontend: ");
-        return;
+        xs_node_create(xenbus->xsh, XBT_NULL, xendev->frontend_path, perms,
+                       ARRAY_SIZE(perms), &local_err);
+        if (local_err) {
+            error_propagate_prepend(errp, local_err,
+                                    "failed to create frontend: ");
+            return;
+        }
     }
 
     xendev->frontend_state_watch =
@@ -1290,12 +1303,14 @@ static void xen_device_realize(DeviceState *dev, Error 
**errp)
     xen_device_backend_set_online(xendev, true);
     xen_device_backend_set_state(xendev, XenbusStateInitWait);
 
-    xen_device_frontend_printf(xendev, "backend", "%s",
-                               xendev->backend_path);
-    xen_device_frontend_printf(xendev, "backend-id", "%u",
-                               xenbus->backend_id);
+    if (!xen_device_frontend_exists(xendev)) {
+        xen_device_frontend_printf(xendev, "backend", "%s",
+                                   xendev->backend_path);
+        xen_device_frontend_printf(xendev, "backend-id", "%u",
+                                   xenbus->backend_id);
 
-    xen_device_frontend_set_state(xendev, XenbusStateInitialising, true);
+        xen_device_frontend_set_state(xendev, XenbusStateInitialising, true);
+    }
 
     xendev->exit.notify = xen_device_exit;
     qemu_add_exit_notifier(&xendev->exit);
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#staging

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