[Xen-devel] [RFC / PATCH] libxl: Prevent qemu closing QMP socket on shutdown before libxl is done with it.

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

While this fixes the race and error on shutdown of a HVM guest with 
pci-passthrough,
i don't know if this could give problems in other areas (migration ?),
hence posted as RFC.

--
Sander

8< -----------
At present on shutdown when using pci-passthrough with qemu-xen, qemu closes 
the QMP
socket before libxl is done with it causing these errors to be logged by libxl:

    Waiting for domain test (domid 1) to die [pid 11568]
    Domain 1 has shut down, reason code 0 0x0
    Action for shutdown reason code 0 is destroy
    Domain 1 needs to be cleaned up: destroying the domain
    libxl: error: libxl_qmp.c:443:qmp_next: Socket read error: Connection reset 
by peer
    libxl: error: libxl_qmp.c:701:libxl__qmp_initialize: Failed to connect to 
QMP
    libxl: error: libxl_qmp.c:686:libxl__qmp_initialize: Connection error: 
Connection refused
    libxl: error: libxl_dm.c:1588:kill_device_model: Device Model already exited
    Done. Exiting now

Prevent this by using the qemu '-no-shutdown' parameter which is described as 
doing:
    "Donât exit QEMU on guest shutdown, but instead only stop the emulation.
     This allows for instance switching to monitor to commit changes to the 
disk image."

So Qemu will stop emulating, but keeps the QMP socket open and waits for libxl 
to
kill the qemu process when it is done, preventing the race and resulting in this
to be logged by libxl:

    Waiting for domain test (domid 1) to die [pid 10859]
    Domain 1 has shut down, reason code 0 0x0
    Action for shutdown reason code 0 is destroy
    Domain 1 needs to be cleaned up: destroying the domain
    Done. Exiting now

Signed-off-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
---
 tools/libxl/libxl_dm.c |    1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index fc3f5a7..3152c87 100644
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -435,6 +435,7 @@ static char ** libxl__build_device_model_args_new(libxl__gc 
*gc,
                                     "path=%s/qmp-libxl-%d,server,nowait",
                                     libxl__run_dir_path(), guest_domid));
 
+    flexarray_append(dm_args, "-no-shutdown");
     flexarray_append(dm_args, "-mon");
     flexarray_append(dm_args, "chardev=libxl-cmd,mode=control");
 
-- 
1.7.10.4


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