[Libguestfs] [PATCH] common/mltools: Add a debug statement when we try to run a non-existent program.

[Richard W.M. Jones]

Previously:

  $ virt-v2v -v -x -i disk fedora-28.img -o openstack -oo server-id=foo
  virt-v2v: libguestfs 1.39.11fedora=29,release=1.fc29,libvirt (x86_64)
  libvirt version: 4.5.0
  virt-v2v: error: openstack: precheck failed, there may be a problem with
  authentication, see earlier error messages
  rm -rf '/var/tmp/null.dTxRFN'

Notice there is no "earlier error message".

After this commit the error changes to:

  openstack: executable not found
  virt-v2v: error: openstack: precheck failed, there may be a problem with
  authentication, see earlier error messages
---
 common/mltools/tools_utils.ml | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/common/mltools/tools_utils.ml b/common/mltools/tools_utils.ml
index ad08d05eb..298d89b4d 100644
--- a/common/mltools/tools_utils.ml
+++ b/common/mltools/tools_utils.ml
@@ -420,9 +420,11 @@ and do_run ?(echo_cmd = true) ?stdout_fd ?stderr_fd args =
     Either (pid, app, stdout_fd, stderr_fd)
   with
   | Executable_not_found _ ->
-    Or 127
-  | Unix.Unix_error (errcode, _, _) when errcode = Unix.ENOENT ->
-    Or 127
+     debug "%s: executable not found" app;
+     Or 127
+  | Unix.Unix_error (errcode, fn, _) when errcode = Unix.ENOENT ->
+     debug "%s: %s: executable not found" app fn;
+     Or 127
 
 and do_teardown app outfd errfd exitstat =
   Option.may Unix.close outfd;
-- 
2.19.0.rc0