[QEMU HCI-8.0 PATCH v2 04/13] usb-host: preserve hostdev FD during CPR migration #VSTOR-137800

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

In .realize(), save freshly opened host device FD into the CPR registry,
and then reuse it on CPR target.  Also, add deletion of that FD from
registry to usb_host_open() / usb_host_close() cleanup paths.

For this to work, we also need to skip the .post-load() code which
closes, detaches the device, and then rescans the host bus to reopen
matching hostdevs.  For the CPR-case migration we don't want any of that
as the hostdev FD stays preserved, and the guest shouldn't notice the
switchover.

Signed-off-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 hw/usb/host-libusb.c | 53 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 51 insertions(+), 2 deletions(-)

diff --git a/hw/usb/host-libusb.c b/hw/usb/host-libusb.c
index 86f96087085..eaacfd34c54 100644
--- a/hw/usb/host-libusb.c
+++ b/hw/usb/host-libusb.c
@@ -47,6 +47,7 @@
 
 #include "qapi/error.h"
 #include "migration/blocker.h"
+#include "migration/cpr.h"
 #include "migration/vmstate.h"
 #include "monitor/monitor.h"
 #include "qemu/error-report.h"
@@ -947,6 +948,38 @@ static void usb_host_ep_update(USBHostDevice *s)
     libusb_free_config_descriptor(conf);
 }
 
+static char *usb_host_cpr_fd_name(USBHostDevice *s)
+{
+    /*
+     * Prefix the CPR fd registry key so it can't collide with a chardev
+     * label or netdev id in the same flat namespace.
+     */
+    return DEVICE(s)->id ?
+        g_strdup_printf("usb-host/%s", DEVICE(s)->id) : NULL;
+}
+
+static int usb_host_cpr_find_fd(USBHostDevice *s)
+{
+    g_autofree char *name = usb_host_cpr_fd_name(s);
+    return name ? cpr_find_fd(name, 0) : -1;
+}
+
+static void usb_host_cpr_save_fd(USBHostDevice *s, int fd)
+{
+    g_autofree char *name = usb_host_cpr_fd_name(s);
+    if (name) {
+        cpr_save_fd(name, 0, fd);
+    }
+}
+
+static void usb_host_cpr_delete_fd(USBHostDevice *s)
+{
+    g_autofree char *name = usb_host_cpr_fd_name(s);
+    if (name) {
+        cpr_delete_fd(name, 0);
+    }
+}
+
 static int usb_host_open(USBHostDevice *s, libusb_device *dev, int hostfd)
 {
     USBDevice *udev = USB_DEVICE(s);
@@ -1069,6 +1102,7 @@ fail:
         s->dev = NULL;
     }
     if (s->hostfd != -1) {
+        usb_host_cpr_delete_fd(s);
         close(s->hostfd);
         s->hostfd = -1;
     }
@@ -1130,6 +1164,7 @@ static int usb_host_close(USBHostDevice *s)
     s->dev = NULL;
 
     if (s->hostfd != -1) {
+        usb_host_cpr_delete_fd(s);
         close(s->hostfd);
         s->hostfd = -1;
     }
@@ -1218,9 +1253,13 @@ static void usb_host_realize(USBDevice *udev, Error **errp)
     if (s->hostdevice) {
         int fd;
         s->needs_autoscan = false;
-        fd = qemu_open(s->hostdevice, O_RDWR, errp);
+        fd = usb_host_cpr_find_fd(s);
         if (fd < 0) {
-            return;
+            fd = qemu_open(s->hostdevice, O_RDWR, errp);
+            if (fd < 0) {
+                return;
+            }
+            usb_host_cpr_save_fd(s, fd);
         }
         rc = usb_host_open(s, NULL, fd);
         if (rc < 0) {
@@ -1757,6 +1796,16 @@ static int usb_host_post_load(void *opaque, int version_id)
 {
     USBHostDevice *dev = opaque;
 
+    /*
+     * For CPR migration, device wasn't released/reset, and the guest
+     * is unaware of the switchover.  The detach/rescan performed in
+     * usb_host_post_load_bh() only exists for cross-host migration.
+     * Skip it for CPR.
+     */
+    if (cpr_is_incoming()) {
+        return 0;
+    }
+
     if (!dev->bh_postld) {
         dev->bh_postld = qemu_bh_new_guarded(usb_host_post_load_bh, dev,
                                              &DEVICE(dev)->mem_reentrancy_guard);
-- 
2.47.1