[PATCH 07/19] libxc: suspend: Rename, improve xc_suspend_evtchn_init

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

xc_suspend_evtchn_init expects to eat the first event on the xce.  If
the xce is used for any other purpose then this can break.  Document
this fact and rename the function to xc_suspend_evtchn_init_exclusive.
(I haven't checked the call sites for improper shared use of the xce.)

Provide a corresponding xc_suspend_evtchn_init_sane which doesn't try
to eat an event, and instead leaves the caller the ability to
demultiplex.

Also document that xc_await_suspend needs exclusive use of the xce.

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>
CC: Shriram Rajagopalan <rshriram@cs.ubc.ca>
---
 tools/libxc/xc_suspend.c                           |   21 ++++++++++++++++----
 tools/libxc/xenguest.h                             |   13 +++++++++++-
 tools/libxl/libxl_dom.c                            |    2 +-
 tools/misc/xen-hptool.c                            |    2 +-
 .../python/xen/lowlevel/checkpoint/libcheckpoint.c |    2 +-
 tools/xcutils/xc_save.c                            |    2 +-
 6 files changed, 33 insertions(+), 9 deletions(-)

diff --git a/tools/libxc/xc_suspend.c b/tools/libxc/xc_suspend.c
index 1ace411..7968a44 100644
--- a/tools/libxc/xc_suspend.c
+++ b/tools/libxc/xc_suspend.c
@@ -14,6 +14,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#include <assert.h>
+
 #include "xc_private.h"
 #include "xenguest.h"
 
@@ -102,7 +104,7 @@ int xc_suspend_evtchn_release(xc_interface *xch, xc_evtchn *xce, int domid, int
     return unlock_suspend_event(xch, domid);
 }
 
-int xc_suspend_evtchn_init(xc_interface *xch, xc_evtchn *xce, int domid, int port)
+int xc_suspend_evtchn_init_sane(xc_interface *xch, xc_evtchn *xce, int domid, int port)
 {
     int rc, suspend_evtchn = -1;
 
@@ -121,9 +123,6 @@ int xc_suspend_evtchn_init(xc_interface *xch, xc_evtchn *xce, int domid, int por
         goto cleanup;
     }
 
-    /* event channel is pending immediately after binding */
-    xc_await_suspend(xch, xce, suspend_evtchn);
-
     return suspend_evtchn;
 
 cleanup:
@@ -132,3 +131,17 @@ cleanup:
 
     return -1;
 }
+
+int xc_suspend_evtchn_init_exclusive(xc_interface *xch, xc_evtchn *xce, int domid, int port)
+{
+    int suspend_evtchn;
+
+    suspend_evtchn = xc_suspend_evtchn_init_sane(xch, xce, domid, port);
+    if (suspend_evtchn < 0)
+        return suspend_evtchn;
+
+    /* event channel is pending immediately after binding */
+    xc_await_suspend(xch, xce, suspend_evtchn);
+
+    return suspend_evtchn;
+}
diff --git a/tools/libxc/xenguest.h b/tools/libxc/xenguest.h
index a0e30e1..ce5456c 100644
--- a/tools/libxc/xenguest.h
+++ b/tools/libxc/xenguest.h
@@ -256,10 +256,21 @@ int xc_hvm_build_target_mem(xc_interface *xch,
 
 int xc_suspend_evtchn_release(xc_interface *xch, xc_evtchn *xce, int domid, int suspend_evtchn);
 
-int xc_suspend_evtchn_init(xc_interface *xch, xc_evtchn *xce, int domid, int port);
+/**
+ * This function eats the initial notification.
+ * xce must not be used for anything else
+ */
+int xc_suspend_evtchn_init_exclusive(xc_interface *xch, xc_evtchn *xce, int domid, int port);
 
+/* xce must not be used for anything else */
 int xc_await_suspend(xc_interface *xch, xc_evtchn *xce, int suspend_evtchn);
 
+/**
+ * The port will be signaled immediately after this call
+ * The caller should check the domain status and look for the next event
+ */
+int xc_suspend_evtchn_init_sane(xc_interface *xch, xc_evtchn *xce, int domid, int port);
+
 int xc_get_bit_size(xc_interface *xch,
                     const char *image_name, const char *cmdline,
                     const char *features, int *type);
diff --git a/tools/libxl/libxl_dom.c b/tools/libxl/libxl_dom.c
index 55f74b2..4b42856 100644
--- a/tools/libxl/libxl_dom.c
+++ b/tools/libxl/libxl_dom.c
@@ -1358,7 +1358,7 @@ void libxl__domain_suspend(libxl__egc *egc, libxl__domain_suspend_state *dss)
 
         if (port >= 0) {
             dss->suspend_eventchn =
-                xc_suspend_evtchn_init(CTX->xch, dss->xce, dss->domid, port);
+                xc_suspend_evtchn_init_exclusive(CTX->xch, dss->xce, dss->domid, port);
 
             if (dss->suspend_eventchn < 0)
                 LOG(WARN, "Suspend event channel initialization failed");
diff --git a/tools/misc/xen-hptool.c b/tools/misc/xen-hptool.c
index 24c3e95..db76f79 100644
--- a/tools/misc/xen-hptool.c
+++ b/tools/misc/xen-hptool.c
@@ -112,7 +112,7 @@ static int suspend_guest(xc_interface *xch, xc_evtchn *xce, int domid, int *evtc
         fprintf(stderr, "DOM%d: No suspend port, try live migration\n", domid);
         goto failed;
     }
-    suspend_evtchn = xc_suspend_evtchn_init(xch, xce, domid, port);
+    suspend_evtchn = xc_suspend_evtchn_init_exclusive(xch, xce, domid, port);
     if (suspend_evtchn < 0)
     {
         fprintf(stderr, "Suspend evtchn initialization failed\n");
diff --git a/tools/python/xen/lowlevel/checkpoint/libcheckpoint.c b/tools/python/xen/lowlevel/checkpoint/libcheckpoint.c
index 01c0d47..817d272 100644
--- a/tools/python/xen/lowlevel/checkpoint/libcheckpoint.c
+++ b/tools/python/xen/lowlevel/checkpoint/libcheckpoint.c
@@ -360,7 +360,7 @@ static int setup_suspend_evtchn(checkpoint_state* s)
     return -1;
   }
 
-  s->suspend_evtchn = xc_suspend_evtchn_init(s->xch, s->xce, s->domid, port);
+  s->suspend_evtchn = xc_suspend_evtchn_init_exclusive(s->xch, s->xce, s->domid, port);
   if (s->suspend_evtchn < 0) {
       s->errstr = "failed to bind suspend event channel";
       return -1;
diff --git a/tools/xcutils/xc_save.c b/tools/xcutils/xc_save.c
index e34bd2c..974f706 100644
--- a/tools/xcutils/xc_save.c
+++ b/tools/xcutils/xc_save.c
@@ -202,7 +202,7 @@ main(int argc, char **argv)
         else
         {
             si.suspend_evtchn =
-              xc_suspend_evtchn_init(si.xch, si.xce, si.domid, port);
+              xc_suspend_evtchn_init_exclusive(si.xch, si.xce, si.domid, port);
 
             if (si.suspend_evtchn < 0)
                 warnx("suspend event channel initialization failed, "
-- 
1.7.10.4