[PATCH 2/3] libxl: save helper: transport errno with all callback return values

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

Whenever we plumb the return value from a callback, plumb through
errno as well.

libxl__xc_domain_saverestore_async_callback_done now assumes that its
caller has set errno sensibly, although this is probably not true :-/.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
---
 tools/libxl/libxl_save_callout.c   |   11 +++++++----
 tools/libxl/libxl_save_msgs_gen.pl |   10 +++++++---
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/tools/libxl/libxl_save_callout.c b/tools/libxl/libxl_save_callout.c
index 1c9f806..88b406b 100644
--- a/tools/libxl/libxl_save_callout.c
+++ b/tools/libxl/libxl_save_callout.c
@@ -138,10 +138,11 @@ void libxl__xc_domain_save(libxl__egc *egc, libxl__domain_suspend_state *dss)
 
 
 void libxl__xc_domain_saverestore_async_callback_done(libxl__egc *egc,
-                           libxl__save_helper_state *shs, int return_value)
+                           libxl__save_helper_state *shs,
+                           int return_value)
 {
     shs->egc = egc;
-    libxl__srm_callout_sendreply(return_value, shs);
+    libxl__srm_callout_sendreply(return_value, errno, shs);
     shs->egc = 0;
 }
 
@@ -356,15 +357,16 @@ libxl__srm_callout_get_callbacks_restore(void *user)
     return &shs->callbacks.restore.a;
 }
 
-void libxl__srm_callout_sendreply(int r, void *user)
+void libxl__srm_callout_sendreply(int r, int savederrno, void *user)
 {
     libxl__save_helper_state *shs = user;
     libxl__egc *egc = shs->egc;
     STATE_AO_GC(shs->ao);
     int errnoval;
+    int data[2] = { r, savederrno };
 
     errnoval = libxl_write_exactly(CTX, libxl__carefd_fd(shs->pipes[0]),
-                                   &r, sizeof(r), shs->stdin_what,
+                                   data, sizeof(data), shs->stdin_what,
                                    "callback return value");
     if (errnoval)
         helper_failed(egc, shs, ERROR_FAIL);
@@ -397,5 +399,6 @@ int libxl__srm_callout_callback_complete(int retval, int errnoval,
     shs->retval = retval;
     shs->errnoval = errnoval;
     libxl__ev_fd_deregister(gc, &shs->readable);
+    errno = 0;
     return 0;
 }
diff --git a/tools/libxl/libxl_save_msgs_gen.pl b/tools/libxl/libxl_save_msgs_gen.pl
index ddd13e5..3d89de9 100755
--- a/tools/libxl/libxl_save_msgs_gen.pl
+++ b/tools/libxl/libxl_save_msgs_gen.pl
@@ -66,6 +66,7 @@ foreach my $ah (qw(callout helper)) {
 #include <string.h>
 #include <stdint.h>
 #include <limits.h>
+#include <errno.h>
 END_BOTH
 
 #include "libxl_internal.h"
@@ -103,7 +104,7 @@ our $getcallbacks = "${libxl}_callout_get_callbacks";
 our $enumcallbacks = "${libxl}_callout_enumcallbacks";
 sub cbtype ($) { "${libxl}_".$_[0]."_autogen_callbacks"; };
 
-f_decl($sendreply, 'callout', 'void', "(int r, void *user)");
+f_decl($sendreply, 'callout', 'void', "(int r, int savederrno, void *user)");
 
 our $helper = "helper";
 our $encode = "${helper}_stub";
@@ -328,7 +329,7 @@ END_ALWAYS
 	$f_more_sr->("        $c_make_callback;\n");
     } else {
         $f_more_sr->("        r = $c_make_callback;\n".
-                     "        $sendreply(r, user);\n");
+                     "        $sendreply(r, errno, user);\n");
     }
     if ($flags =~ m/x/) {
         my $c_v = "(1u<<$msgnum)";
@@ -354,9 +355,12 @@ END_ALWAYS
 	f_more("${encode}_$name",
                (<<END_ALWAYS.($debug ? <<END_DEBUG : '').<<END_ALWAYS));
     int r = ${helper}_getreply(user);
+    int savederrno = ${helper}_getreply(user);
 END_ALWAYS
-    fprintf(stderr,"libxl-save-helper: $name got reply %d\\n",r);
+    fprintf(stderr,"libxl-save-helper: $name got reply %d (errno: %s)\\n",
+            r,strerror(savederrno));
 END_DEBUG
+    errno = savederrno;
     return r;
 END_ALWAYS
     }
-- 
1.7.10.4