[QEMU HCI-8.0 PATCH v2 13/13] usb-host: make CPR migration blocker conditional #VSTOR-137800

[Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>]

A previous commit added an unconditional blocker for CPR migrations.
That is to refuse CPR gracefully instead of crashing and for the previous
commits to remain bisectable.

Now the restore path is complete: the FD is preserved, in-flight URBs
are drained and replayed, the device is handed off across cpr-transfer,
and the endpoints and isochronous streams are reconstructed on the
target.  So let's lift the CPR blocker for the devices which satisfy the
preconditions.

Still, the remaining preconditions for CPR to work are:

  * We must open host device FD ourselves, so that libusb owns the FD.
    This way we're able to preserve the FD during CPR;
  * Device ID must be provided as a unique stable key for CPR FD registry.

Use them to guard the blocker addition.  Apart from that, prohibit CPR on
WIN32 platform and on hosts with older libusb versions.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 hw/usb/host-libusb.c | 50 +++++++++++++++++++++++++++++++-------------
 1 file changed, 35 insertions(+), 15 deletions(-)

diff --git a/hw/usb/host-libusb.c b/hw/usb/host-libusb.c
index d12e04c2768..da0ff801661 100644
--- a/hw/usb/host-libusb.c
+++ b/hw/usb/host-libusb.c
@@ -1449,24 +1449,44 @@ static void usb_host_realize(USBDevice *udev, Error **errp)
     s->exit.notify = usb_host_exit_notifier;
     qemu_add_exit_notifier(&s->exit);
 
-#if LIBUSB_API_VERSION >= 0x01000107 && !defined(CONFIG_WIN32)
-    if (s->hostdevice && DEVICE(s)->id) {
-        migration_add_notifier_modes(&s->cpr_notifier, usb_host_cpr_notifier,
-                                     MIG_MODE_CPR_TRANSFER,
-                                     MIG_MODE_CPR_EXEC, -1);
+#ifdef CONFIG_WIN32
+    error_setg(&s->cpr_blocker,
+               "usb-host device %s does not support CPR: "
+               "WIN32 platform is not supported",
+               DEVICE(s)->id ?: "(anonymous)");
+#elif LIBUSB_API_VERSION < 0x01000107
+    error_setg(&s->cpr_blocker,
+               "usb-host device %s does not support CPR: "
+               "libusb API version 0x%08x is too old",
+               DEVICE(s)->id ?: "(anonymous)", (unsigned) LIBUSB_API_VERSION);
+#else
+    if (!(s->hostdevice && DEVICE(s)->id)) {
+        /*
+         * Host FD must be owned by libusb to support CPR migration.  That's
+         * equivalent to hostdevice= property being present.   Also device ID
+         * is required as stable key for CPR FD registry.
+         */
+        error_setg(&s->cpr_blocker,
+                   "usb-host device %s does not support CPR: "
+                   "hostdevice= and a device id are required",
+                   DEVICE(s)->id ?: "(anonymous)");
     }
 #endif
 
-    error_setg(&s->cpr_blocker, "usb-host device %s does not support CPR: ",
-               DEVICE(s)->id ?: "(anonymous)");
-    if (migrate_add_blocker_modes(&s->cpr_blocker, errp,
-                                  MIG_MODE_CPR_TRANSFER,
-                                  MIG_MODE_CPR_EXEC, -1) < 0) {
-        qemu_remove_exit_notifier(&s->exit);
-        if (s->needs_autoscan) {
-            QTAILQ_REMOVE(&hostdevs, s, next);
-        }
-        usb_host_close(s);
+    if (s->cpr_blocker) {
+        if (migrate_add_blocker_modes(&s->cpr_blocker, errp,
+                                      MIG_MODE_CPR_TRANSFER,
+                                      MIG_MODE_CPR_EXEC, -1) < 0) {
+            qemu_remove_exit_notifier(&s->exit);
+            if (s->needs_autoscan) {
+                QTAILQ_REMOVE(&hostdevs, s, next);
+            }
+            usb_host_close(s);
+        }
+    } else {
+        migration_add_notifier_modes(&s->cpr_notifier, usb_host_cpr_notifier,
+                                     MIG_MODE_CPR_TRANSFER,
+                                     MIG_MODE_CPR_EXEC, -1);
     }
 }
 
-- 
2.47.1