[PATCH 08/23] libxl: events: Provide libxl__xswait_*

[Ian Jackson <ian.jackson@eu.citrix.com>]

This is an ao utility for for conveniently doing a timed wait on
xenstore.  It handles setting up and cancelling the timeout, and also
conveniently reads the key for you.

No callers yet in this patch.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
CC: Ian Campbell <ian.campbell@citrix.com>
---
 tools/libxl/libxl_aoutils.c  |   77 ++++++++++++++++++++++++++++++++++++++++++
 tools/libxl/libxl_internal.h |   52 ++++++++++++++++++++++++++++
 2 files changed, 129 insertions(+)

diff --git a/tools/libxl/libxl_aoutils.c b/tools/libxl/libxl_aoutils.c
index b4eb6e5..477717b 100644
--- a/tools/libxl/libxl_aoutils.c
+++ b/tools/libxl/libxl_aoutils.c
@@ -16,6 +16,83 @@
 
 #include "libxl_internal.h"
 
+/*----- xswait -----*/
+
+static libxl__ev_xswatch_callback xswait_xswatch_callback;
+static libxl__ev_time_callback xswait_timeout_callback;
+static void xswait_report_error(libxl__egc*, libxl__xswait_state*, int rc);
+
+void libxl__xswait_init(libxl__xswait_state *xswa)
+{
+    libxl__ev_time_init(&xswa->time_ev);
+    libxl__ev_xswatch_init(&xswa->watch_ev);
+}
+
+void libxl__xswait_stop(libxl__gc *gc, libxl__xswait_state *xswa)
+{
+    libxl__ev_time_deregister(gc, &xswa->time_ev);
+    libxl__ev_xswatch_deregister(gc, &xswa->watch_ev);
+}
+
+bool libxl__xswait_inuse(const libxl__xswait_state *xswa)
+{
+    bool time_inuse = libxl__ev_time_isregistered(&xswa->time_ev);
+    bool watch_inuse = libxl__ev_xswatch_isregistered(&xswa->watch_ev);
+    assert(time_inuse == watch_inuse);
+    return time_inuse;
+}
+
+int libxl__xswait_start(libxl__gc *gc, libxl__xswait_state *xswa)
+{
+    int rc;
+
+    rc = libxl__ev_time_register_rel(gc, &xswa->time_ev,
+                                     xswait_timeout_callback, xswa->timeout_ms);
+    if (rc) goto err;
+
+    rc = libxl__ev_xswatch_register(gc, &xswa->watch_ev,
+                                    xswait_xswatch_callback, xswa->path);
+    if (rc) goto err;
+
+    return 0;
+
+ err:
+    libxl__xswait_stop(gc, xswa);
+    return rc;
+}
+
+void xswait_xswatch_callback(libxl__egc *egc, libxl__ev_xswatch *xsw,
+                             const char *watch_path, const char *event_path)
+{
+    EGC_GC;
+    libxl__xswait_state *xswa = CONTAINER_OF(xsw, *xswa, watch_ev);
+    int rc;
+    const char *data;
+
+    rc = libxl__xs_read_checked(gc, XBT_NULL, xswa->path, &data);
+    if (rc) { xswait_report_error(egc, xswa, rc); return; }
+
+    xswa->callback(egc, xswa, 0, data);
+}
+
+void xswait_timeout_callback(libxl__egc *egc, libxl__ev_time *ev,
+                             const struct timeval *requested_abs)
+{
+    EGC_GC;
+    libxl__xswait_state *xswa = CONTAINER_OF(ev, *xswa, time_ev);
+    LOG(DEBUG, "%s: xswait timeout (path=%s)", xswa->what, xswa->path);
+    xswait_report_error(egc, xswa, ERROR_TIMEDOUT);
+}
+
+static void xswait_report_error(libxl__egc *egc, libxl__xswait_state *xswa,
+                                int rc)
+{
+    EGC_GC;
+    libxl__xswait_stop(gc, xswa);
+    xswa->callback(egc, xswa, rc, 0);
+}
+
+
 /*----- data copier -----*/
 
 void libxl__datacopier_init(libxl__datacopier_state *dc)
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 51d6c6d..36de135 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1068,6 +1068,58 @@ _hidden int libxl__create_pci_backend(libxl__gc *gc, uint32_t domid,
                                       libxl_device_pci *pcidev, int num);
 _hidden int libxl__device_pci_destroy_all(libxl__gc *gc, uint32_t domid);
 
+/*----- xswait: wait for a xenstore node to be suitable -----*/
+
+typedef struct libxl__xswait_state libxl__xswait_state;
+
+/*
+ * rc describes the circumstances of this callback:
+ *
+ * rc==0
+ *
+ *     The xenstore path (may have) changed.  It has been read for
+ *     you.  The result is in data (allocated from the ao gc).
+ *     data may be NULL, which means that the xenstore read gave
+ *     ENOENT.
+ *
+ *     If you are satisfied, you MUST call libxl__xswait_stop.
+ *     Otherwise, xswait will continue waiting and watching and
+ *     will call you back later.
+ *
+ * rc==ETIMEDOUT
+ *
+ *     The specified timeout was reached.
+ *     This has NOT been logged (except to the debug log).
+ *     xswait will not continue (but calling libxl__xswait_stop is OK).
+ *
+ * rc!=0
+ *
+ *     Some other error occurred.
+ *     This HAS been logged.
+ *     xswait will not continue (but calling libxl__xswait_stop is OK).
+ *
+ */
+typedef void libxl__xswait_callback(libxl__egc *egc,
+      libxl__xswait_state *xswa, int rc, const char *data);
+
+struct libxl__xswait_state {
+    /* caller must fill these in, and they must all remain valid */
+    libxl__ao *ao;
+    const char *what; /* for error msgs: noun phrase, what we're waiting for */
+    const char *path;
+    int timeout_ms; /* as for poll(2) */
+    libxl__xswait_callback *callback;
+    /* remaining fields are private to xswait */
+    libxl__ev_time time_ev;
+    libxl__ev_xswatch watch_ev;
+};
+
+void libxl__xswait_init(libxl__xswait_state*);
+void libxl__xswait_stop(libxl__gc*, libxl__xswait_state*); /*idempotent*/
+bool libxl__xswait_inuse(const libxl__xswait_state *ss);
+
+int libxl__xswait_start(libxl__gc*, libxl__xswait_state*);
+
 /*
  *----- spawn -----
  *
-- 
1.7.10.4