[RFC v2 6/9] libxl: Have QEMU save its state to a file descriptor

[Anthony PERARD <anthony.perard@citrix.com>]

In case QEMU have restricted access to the system, open the file for it,
and QEMU will save its state to this file descritor.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 tools/libxl/libxl_qmp.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/tools/libxl/libxl_qmp.c b/tools/libxl/libxl_qmp.c
index 28bc2cabcd..3bb0f28bea 100644
--- a/tools/libxl/libxl_qmp.c
+++ b/tools/libxl/libxl_qmp.c
@@ -989,25 +989,61 @@ int libxl__qmp_system_wakeup(libxl__gc *gc, int domid)
     return qmp_run_command(gc, domid, "system_wakeup", NULL, NULL, NULL);
 }
 
+/* Find out which fdset have been allocated */
+static int qmp_fdset_add_fd_callback(libxl__qmp_handler *qmp,
+                                     const libxl__json_object *ret,
+                                     void *opaque)
+{
+    const libxl__json_object *o;
+    int fdset;
+
+    o = libxl__json_map_get("fdset-id", ret, JSON_INTEGER);
+    if (!o)
+        return 1;
+
+    fdset = libxl__json_object_get_integer(o);
+    *(int*)opaque = fdset;
+    return 0;
+}
+
 int libxl__qmp_save(libxl__gc *gc, int domid, const char *filename, bool live)
 {
     libxl__json_object *args = NULL;
     libxl__qmp_handler *qmp = NULL;
     int rc;
+    int state_fd;
+    int new_fdset;
 
     qmp = libxl__qmp_initialize(gc, domid);
     if (!qmp)
         return ERROR_FAIL;
 
-    qmp_parameters_add_string(gc, &args, "filename", (char *)filename);
+    state_fd = open(filename, O_WRONLY | O_CREAT, 0600);
+    if (state_fd < 0) {
+        LOGED(ERROR, domid,
+              "Failed to open file %s for QEMU", filename);
+        goto out;
+    }
+
+    qmp->fd_to_send = state_fd;
+
+    rc = qmp_synchronous_send(qmp, "add-fd", NULL,
+                              qmp_fdset_add_fd_callback, &new_fdset,
+                              qmp->timeout);
+    if (rc)
+        goto out;
 
     /* live parameter was added to QEMU 2.11. It signal QEMU that the save
      * operation is for a live migration rather that for taking a snapshot. */
     if (qmp_qemu_check_version(qmp, 2, 11, 0))
         qmp_parameters_add_bool(gc, &args, "live", live);
 
+    QMP_PARAMETERS_SPRINTF(&args, "filename", "/dev/fdset/%d", new_fdset);
     rc = qmp_synchronous_send(qmp, "xen-save-devices-state", args,
                               NULL, NULL, qmp->timeout);
+out:
+    if (state_fd >= 0)
+        close(state_fd);
     libxl__qmp_close(qmp);
     return rc;
 }
-- 
Anthony PERARD


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