[PATCH v8 07/17] libxl_exec: Add libxl__spawn_initiate_failure

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

This function can be used by user of libxl__spawn_* when they setup a
notification other than xenstore. The parent can already report success
via libxl__spawn_initiate_detach(), this new function can be used for
failure instead of waiting for the timeout.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
---

Notes:
    v8:
        Acked
    
    v7:
        call spawn_fail from libxl__spawn_initiate_failure.
        modify spawn_fail to set ss->rc only once.
        Fix description to tell caller of libxl__spawn_initiate_failure that
            they have to log.
        use an `egc` instead of `gc` with libxl__spawn_initiate_failure.
    
    v6:
        long line fix
        typos fixed
        fix leak of internal state into external doc
        if the function is call multiple times, set rc only the first time.
    
    v5:
        fix typos

 tools/libxl/libxl_exec.c     | 11 ++++++++++-
 tools/libxl/libxl_internal.h | 23 ++++++++++++++++++++++-
 2 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/tools/libxl/libxl_exec.c b/tools/libxl/libxl_exec.c
index 02e6c917f0..47c9c8f1ba 100644
--- a/tools/libxl/libxl_exec.c
+++ b/tools/libxl/libxl_exec.c
@@ -373,13 +373,22 @@ void libxl__spawn_initiate_detach(libxl__gc *gc, libxl__spawn_state *ss)
     spawn_detach(gc, ss);
 }
 
+void libxl__spawn_initiate_failure(libxl__egc *egc, libxl__spawn_state *ss,
+                                   int rc)
+/* The spawn state must be Attached on entry and will be Attached Failed
+ * on return.  */
+{
+    spawn_fail(egc, ss, rc);
+}
+
 static void spawn_fail(libxl__egc *egc, libxl__spawn_state *ss, int rc)
 /* Caller must have logged.  Must be last thing in calling function,
  * as it may make the callback.  Precondition: Attached or Detaching. */
 {
     EGC_GC;
     assert(rc);
-    ss->rc = rc;
+    if (!ss->rc)
+        ss->rc = rc;
     spawn_detach(gc, ss);
 }
 
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index be18d4f341..9e7e4dcae9 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -1567,7 +1567,8 @@ _hidden void libxl__spawn_init(libxl__spawn_state*);
  *
  * The inner child must soon exit or exec.  It must also soon exit or
  * notify the parent of its successful startup by writing to the
- * xenstore path xspath.
+ * xenstore path xspath OR via other means that the parent will have
+ * to set up.
  *
  * The user (in the parent) will be called back (confirm_cb) every
  * time that xenstore path is modified.
@@ -1623,6 +1624,26 @@ _hidden int libxl__spawn_spawn(libxl__egc *egc, libxl__spawn_state *spawn);
  */
 _hidden void libxl__spawn_initiate_detach(libxl__gc *gc, libxl__spawn_state*);
 
+/*
+ * libxl__spawn_initiate_failure - Propagate failure from the caller to the
+ * callee.
+ *
+ * Works by killing the intermediate process from spawn_spawn.
+ * After this function returns, a failure will be reported.
+ *
+ * This is not synchronous: there will be a further callback when
+ * the detach is complete.
+ *
+ * Caller must have logged a failure reason.
+ *
+ * The spawn state must be Attached on entry and will remain Attached. It
+ * is possible for a spawn to fail for multiple reasons, for example
+ * call(s) to libxl__spawn_initiate_failure and also for some other reason.
+ * In that case the first rc value from any source will take precedence.
+ */
+_hidden void libxl__spawn_initiate_failure(libxl__egc *egc,
+                                           libxl__spawn_state *ss, int rc);
+
 /*
  * If successful, this should return 0.
  *
-- 
Anthony PERARD


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