[PATCH v5 01/15] libxl: Design of an async API to issue QMP commands to QEMU

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

All the functions will be implemented in later patches.

This patch includes the API that libxl can use to send QMP commands to
QEMU.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---

Notes:
    v5:
        some changes in the comment

 tools/libxl/libxl_internal.h | 72 +++++++++++++++++++++++++++++++++++-
 1 file changed, 70 insertions(+), 2 deletions(-)

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 802382c704..979a9947f0 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -202,6 +202,8 @@ typedef struct libxl__ao libxl__ao;
 typedef struct libxl__aop_occurred libxl__aop_occurred;
 typedef struct libxl__osevent_hook_nexus libxl__osevent_hook_nexus;
 typedef struct libxl__osevent_hook_nexi libxl__osevent_hook_nexi;
+typedef struct libxl__json_object libxl__json_object;
+typedef struct libxl__carefd libxl__carefd;
 
 typedef struct libxl__domain_create_state libxl__domain_create_state;
 typedef void libxl__domain_create_cb(struct libxl__egc *egc,
@@ -357,6 +359,72 @@ struct libxl__ev_child {
     LIBXL_LIST_ENTRY(struct libxl__ev_child) entry;
 };
 
+/*
+ * QMP asynchronous calls
+ *
+ * This facility allows a command to be sent to QEMU, and the response to be
+ * handed to a callback function.
+ *
+ * Commands can be chained, with a same connection. (e.g. "add-fd" will need to
+ * be chained to the next command). A libxl__ev_qmp can be reused when the
+ * callback is been called in order to use the same connection.
+ *
+ * Only one connection at a time can be made to one QEMU, so avoid keeping a
+ * libxl__ev_qmp Connected for to long and call libxl__ev_qmp_dispose as soon
+ * as it is not needed anymore.
+ *
+ * Possible states of a libxl__ev_qmp:
+ *  Undefined
+ *    Might contain anything.
+ *  Idle
+ *    Struct contents are defined enough to pass to any libxl__ev_qmp_*
+ *    function.
+ *    The struct does not contain references to any allocated private resources
+ *    so can be thrown away.
+ *  Active
+ *    Currently waiting for the callback to be called.
+ *    _dispose must be called to reclaim resources.
+ *  Connected
+ *    Struct contain allocated ressources.
+ *    Calling _send() with this same ev will use the same QMP connection.
+ *    _dispose() must be called to reclaim resources.
+ *
+ * libxl__ev_qmp_init: Undefined/Idle -> Idle
+ *
+ * libxl__ev_qmp_send: Idle/Connected -> Active (on error: Idle)
+ *    Sends a command to QEMU.
+ *    callback will be called when a response is received or when an error
+ *    as occured.
+ *
+ * libxl__ev_qmp_dispose: Connected/Active/Idle -> Idle
+ *
+ * callback: When called: Active -> Connected
+ *    When called, ev is Connected and can be reused or disposed of.
+ *    If an error occured, it is called with response == NULL and the error
+ *    code in rc.
+ *    The callback is only called once.
+ */
+typedef struct libxl__ev_qmp libxl__ev_qmp;
+typedef void libxl__ev_qmp_callback(libxl__egc *egc, libxl__ev_qmp *ev,
+                                    const libxl__json_object *response,
+                                    int rc);
+
+_hidden void libxl__ev_qmp_init(libxl__ev_qmp *ev);
+_hidden int libxl__ev_qmp_send(libxl__gc *gc, libxl__ev_qmp *ev,
+                               const char *cmd, libxl__json_object *args);
+_hidden void libxl__ev_qmp_dispose(libxl__gc *gc, libxl__ev_qmp *ev);
+
+struct libxl__ev_qmp {
+    /* caller should include this in their own struct */
+    /* caller must fill these in, and they must all remain valid */
+    uint32_t domid;
+    libxl__ev_qmp_callback *callback;
+    libxl__carefd *cfd; /* set to send a fd with the command, NULL otherwise */
+
+    /* remaining fields are private to libxl_ev_qmp_* */
+    int id;
+};
+
 
 /*
  * evgen structures, which are the state we use for generating
@@ -1902,7 +1970,7 @@ typedef enum {
     JSON_ANY     = 255 /* this is a mask of all values above, adjust as needed */
 } libxl__json_node_type;
 
-typedef struct libxl__json_object {
+struct libxl__json_object {
     libxl__json_node_type type;
     union {
         bool b;
@@ -1915,7 +1983,7 @@ typedef struct libxl__json_object {
         flexarray_t *map;
     } u;
     struct libxl__json_object *parent;
-} libxl__json_object;
+};
 
 typedef int (*libxl__json_parse_callback)(libxl__gc *gc,
                                           libxl__json_object *o,
-- 
Anthony PERARD


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