libxl: ao abort: Support aborting where we spot domain death

Make an active libxl__domaindeathcheck contain an active
libxl__ao_abortable.

Consequential changes are:
 * domaindeath callbacks now take an rc value.
 * libxl__domaindeathcheck_start takes an ao, not a gc.
 * bootloader_domaindeath plumbs the rc through to its caller.
 * libxl__domaindeathcheck_init and _stop are not quite trivial any
   more so are moved from (inline functions) in libxl_internal.h, to
   ordinary functions defined in libxl_event.c.
 * libxl__domaindeathcheck_start is not trivial any more, and now has
   the standard error-handling pattern.

The only current user of libxl__domaindeathcheck is the bootloader.
So the result is that now it is possible to effectively abort domain
creation while the bootloader is running.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
---
v2: New in this version of the series.

tools/libxl/libxl_bootloader.c

@@ -33,7 +33,8 @@ static void bootloader_keystrokes_copyfail(libxl__egc *egc,
        libxl__datacopier_state *dc, int onwrite, int errnoval);
 static void bootloader_display_copyfail(libxl__egc *egc,
        libxl__datacopier_state *dc, int onwrite, int errnoval);
-static void bootloader_domaindeath(libxl__egc*, libxl__domaindeathcheck *dc);
+static void bootloader_domaindeath(libxl__egc*, libxl__domaindeathcheck *dc,
+                                   int rc);
 static void bootloader_finished(libxl__egc *egc, libxl__ev_child *child,
                                 pid_t pid, int status);
 
@@ -496,7 +497,7 @@ static void bootloader_gotptys(libxl__egc *egc, libxl__openpty_state *op)
     bl->deathcheck.what = "stopping bootloader";
     bl->deathcheck.domid = bl->domid;
     bl->deathcheck.callback = bootloader_domaindeath;
-    rc = libxl__domaindeathcheck_start(gc, &bl->deathcheck);
+    rc = libxl__domaindeathcheck_start(ao, &bl->deathcheck);
     if (rc) goto out;
 
     if (bl->console_available)
@@ -610,10 +611,12 @@ static void bootloader_display_copyfail(libxl__egc *egc,
     bootloader_copyfail(egc, "bootloader output", bl, 1, onwrite, errnoval);
 }
 
-static void bootloader_domaindeath(libxl__egc *egc, libxl__domaindeathcheck *dc)
+static void bootloader_domaindeath(libxl__egc *egc,
+                                   libxl__domaindeathcheck *dc,
+                                   int rc)
 {
     libxl__bootloader_state *bl = CONTAINER_OF(dc, *bl, deathcheck);
-    bootloader_stop(egc, bl, ERROR_DOMAIN_DESTROYED);
+    bootloader_stop(egc, bl, rc);
 }
 
 static void bootloader_finished(libxl__egc *egc, libxl__ev_child *child,

tools/libxl/libxl_event.c

@@ -933,6 +933,18 @@ int libxl__ev_devstate_wait(libxl__ao *ao, libxl__ev_devstate *ds,
  * futile.
  */
 
+void libxl__domaindeathcheck_init(libxl__domaindeathcheck *dc)
+{
+    libxl__ao_abortable_init(&dc->abrt);
+    libxl__ev_xswatch_init(&dc->watch);
+}
+
+void libxl__domaindeathcheck_stop(libxl__gc *gc, libxl__domaindeathcheck *dc)
+{
+    libxl__ao_abortable_deregister(&dc->abrt);
+    libxl__ev_xswatch_deregister(gc,&dc->watch);
+}
+
 static void domaindeathcheck_callback(libxl__egc *egc, libxl__ev_xswatch *w,
                             const char *watch_path, const char *event_path)
 {
@@ -941,6 +953,8 @@ static void domaindeathcheck_callback(libxl__egc *egc, libxl__ev_xswatch *w,
     const char *p = libxl__xs_read(gc, XBT_NULL, watch_path);
     if (p) return;
 
+    libxl__domaindeathcheck_stop(gc,dc);
+
     if (errno!=ENOENT) {
         LIBXL__EVENT_DISASTER(egc,"failed to read xenstore"
                               " for domain detach check", errno, 0);
@@ -949,15 +963,43 @@ static void domaindeathcheck_callback(libxl__egc *egc, libxl__ev_xswatch *w,
 
     LOG(ERROR,"%s: domain %"PRIu32" removed (%s no longer in xenstore)",
         dc->what, dc->domid, watch_path);
-    dc->callback(egc, dc);
+    dc->callback(egc, dc, ERROR_DOMAIN_DESTROYED);
 }
 
-int libxl__domaindeathcheck_start(libxl__gc *gc,
+static void domaindeathcheck_abort(libxl__egc *egc,
+                                   libxl__ao_abortable *abrt,
+                                   int rc)
+{
+    libxl__domaindeathcheck *dc = CONTAINER_OF(abrt, *dc, abrt);
+    EGC_GC;
+
+    libxl__domaindeathcheck_stop(gc,dc);
+    dc->callback(egc, dc, rc);
+}
+
+int libxl__domaindeathcheck_start(libxl__ao *ao,
                                   libxl__domaindeathcheck *dc)
 {
+    AO_GC;
+    int rc;
     const char *path = GCSPRINTF("/local/domain/%"PRIu32, dc->domid);
-    return libxl__ev_xswatch_register(gc, &dc->watch,
-                                      domaindeathcheck_callback, path);
+
+    libxl__domaindeathcheck_init(dc);
+
+    dc->abrt.ao = ao;
+    dc->abrt.callback = domaindeathcheck_abort;
+    rc = libxl__ao_abortable_register(&dc->abrt);
+    if (rc) goto out;
+
+    rc = libxl__ev_xswatch_register(gc, &dc->watch,
+                                    domaindeathcheck_callback, path);
+    if (rc) goto out;
+
+    return 0;
+
+ out:
+    libxl__domaindeathcheck_stop(gc,dc);
+    return rc;
 }
 
 /*

tools/libxl/libxl_internal.h

@@ -1263,7 +1263,8 @@ _hidden int libxl__ev_devstate_wait(libxl__ao *ao, libxl__ev_devstate *ds,
 
 typedef struct libxl__domaindeathcheck libxl__domaindeathcheck;
 typedef void libxl___domaindeathcheck_callback(libxl__egc *egc,
-                                         libxl__domaindeathcheck*);
+        libxl__domaindeathcheck*,
+        int rc /* DESTROYED or ABORTED */);
 
 struct libxl__domaindeathcheck {
     /* must be filled in by caller, and remain valid: */
@@ -1271,16 +1272,15 @@ struct libxl__domaindeathcheck {
     uint32_t domid;
     libxl___domaindeathcheck_callback *callback;
     /* private */
+    libxl__ao_abortable abrt;
     libxl__ev_xswatch watch;
 };
 
-_hidden int libxl__domaindeathcheck_start(libxl__gc *gc,
+_hidden int libxl__domaindeathcheck_start(libxl__ao *ao,
                                           libxl__domaindeathcheck *dc);
 
-static inline void libxl__domaindeathcheck_init
- (libxl__domaindeathcheck *dc) { libxl__ev_xswatch_init(&dc->watch); }
-static inline void libxl__domaindeathcheck_stop(libxl__gc *gc,
-  libxl__domaindeathcheck *dc) { libxl__ev_xswatch_deregister(gc,&dc->watch); }
+void libxl__domaindeathcheck_init(libxl__domaindeathcheck *dc);
+void libxl__domaindeathcheck_stop(libxl__gc *gc, libxl__domaindeathcheck *dc);
 
 
 /*