[xen staging] libxl: force netback to wait for hotplug execution before connecting

[patchbot@xxxxxxx]

commit 0bdc43c8dec993258e930b34855853c22b917519
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Thu Jan 27 13:51:19 2022 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Jan 27 13:51:19 2022 +0100

    libxl: force netback to wait for hotplug execution before connecting
    
    By writing an empty "hotplug-status" xenstore node in the backend path
    libxl can force Linux netback to wait for hotplug script execution
    before proceeding to the 'connected' state.
    
    This is required so that netback doesn't skip state 2 (InitWait) and
    thus blocks libxl waiting for such state in order to launch the
    hotplug script (see libxl__wait_device_connection).
    
    Reported-by: James Dingwall <james-xen@xxxxxxxxxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Tested-by: James Dingwall <james-xen@xxxxxxxxxxxxxx>
    Reviewed-by: Paul Durrant <paul@xxxxxxx>
    Tested-by: Julien Grall <jgrall@xxxxxxxxxx>
    Reviewed-by: Wei Liu <wei.liu@xxxxxxxxxx>
---
 tools/libs/light/libxl_nic.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tools/libs/light/libxl_nic.c b/tools/libs/light/libxl_nic.c
index 0b45469dca..0b9e70c9d1 100644
--- a/tools/libs/light/libxl_nic.c
+++ b/tools/libs/light/libxl_nic.c
@@ -248,6 +248,13 @@ static int libxl__set_xenstore_nic(libxl__gc *gc, uint32_t 
domid,
     flexarray_append(ro_front, "mtu");
     flexarray_append(ro_front, GCSPRINTF("%u", nic->mtu));
 
+    /*
+     * Force backend to wait for hotplug script execution before switching to
+     * connected state.
+     */
+    flexarray_append(back, "hotplug-status");
+    flexarray_append(back, "");
+
     return 0;
 }
 
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