libxl: ao abort: Abort libxc save/restore

Register the the save/restore helper interface with the abort
machinery.  When we are informed that save/restore should be aborted,
we make a note of the that in our rc variable, and send the helper a
SIGTERM.  It will die in due course.

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_internal.h

@@ -2702,6 +2702,7 @@ typedef struct libxl__save_helper_state {
     int rc;
     int completed; /* retval/errnoval valid iff completed */
     int retval, errnoval; /* from xc_domain_save / xc_domain_restore */
+    libxl__ao_abortable abrt;
     libxl__carefd *pipes[2]; /* 0 = helper's stdin, 1 = helper's stdout */
     libxl__ev_fd readable;
     libxl__ev_child child;

tools/libxl/libxl_save_callout.c

@@ -32,6 +32,7 @@ static void run_helper(libxl__egc *egc, libxl__save_helper_state *shs,
                        const unsigned long *argnums, int num_argnums);
 
 static void helper_failed(libxl__egc*, libxl__save_helper_state *shs, int rc);
+static void helper_stop(libxl__egc *egc, libxl__ao_abortable*, int rc);
 static void helper_stdout_readable(libxl__egc *egc, libxl__ev_fd *ev,
                                    int fd, short events, short revents);
 static void helper_exited(libxl__egc *egc, libxl__ev_child *ch,
@@ -166,9 +167,15 @@ static void run_helper(libxl__egc *egc, libxl__save_helper_state *shs,
     shs->rc = 0;
     shs->completed = 0;
     shs->pipes[0] = shs->pipes[1] = 0;
+    libxl__ao_abortable_init(&shs->abrt);
     libxl__ev_fd_init(&shs->readable);
     libxl__ev_child_init(&shs->child);
 
+    shs->abrt.ao = shs->ao;
+    shs->abrt.callback = helper_stop;
+    rc = libxl__ao_abortable_register(&shs->abrt);
+    if (rc) goto out;
+
     shs->stdin_what = GCSPRINTF("domain %"PRIu32" save/restore helper"
                                 " stdin pipe", domid);
     shs->stdout_what = GCSPRINTF("domain %"PRIu32" save/restore helper"
@@ -262,6 +269,22 @@ static void helper_failed(libxl__egc *egc, libxl__save_helper_state *shs,
     sendsig(gc, shs, SIGKILL);
 }
 
+static void helper_stop(libxl__egc *egc, libxl__ao_abortable *abrt, int rc)
+{
+    libxl__save_helper_state *shs = CONTAINER_OF(abrt, *shs, abrt);
+    STATE_AO_GC(shs->ao);
+
+    if (!libxl__ev_child_inuse(&shs->child)) {
+        helper_failed(egc, shs, rc);
+        return;
+    }
+
+    if (!shs->rc)
+        shs->rc = rc;
+
+    sendsig(gc, shs, SIGTERM);
+}
+
 static void helper_stdout_readable(libxl__egc *egc, libxl__ev_fd *ev,
                                    int fd, short events, short revents)
 {
@@ -332,6 +355,7 @@ static void helper_done(libxl__egc *egc, libxl__save_helper_state *shs)
 {
     STATE_AO_GC(shs->ao);
 
+    libxl__ao_abortable_deregister(&shs->abrt);
     libxl__ev_fd_deregister(gc, &shs->readable);
     libxl__carefd_close(shs->pipes[0]);  shs->pipes[0] = 0;
     libxl__carefd_close(shs->pipes[1]);  shs->pipes[1] = 0;