v2v: -o openstack: Check openstack binary exists before running it.

Improves the error message when openstack is not installed.

This also mentions the openstack command in the manual page.

v2v/output_openstack.ml

@@ -28,6 +28,9 @@ open Common_gettext.Gettext
 open Types
 open Utils
 
+(* Name of the openstack CLI program (on $PATH). *)
+let openstack_binary = "openstack"
+
 (* Timeout waiting for new Cinder volumes to move to "available" state.
  * We assume this could be quite a long time on backends which want
  * to preallocate the storage.
@@ -157,13 +160,20 @@ class output_openstack output_conn output_password output_storage
       List.push_back args "--insecure";
     !args in
 
+  let error_unless_openstack_command_exists () =
+    try ignore (which openstack_binary)
+    with Executable_not_found _ ->
+      error (f_"the ‘%s’ program is not available.  It is needed to communicate with OpenStack.")
+            openstack_binary
+  in
+
   (* We use this convenient wrapper around [Tools_utils.run_command]
    * for two reasons: (1) Because we want to run openstack with
    * extra_args.  (2) OpenStack commands are noisy so we want to
    * direct stdout to /dev/null unless we're in verbose mode.
    *)
   let run_openstack_command args =
-    let cmd = [ "openstack" ] @ extra_args @ args in
+    let cmd = [ openstack_binary ] @ extra_args @ args in
     let stdout_fd =
       if verbose () then None
       else Some (openfile "/dev/null" [O_WRONLY] 0) in
@@ -176,7 +186,7 @@ class output_openstack output_conn output_password output_storage
    * '-f json' to the args yourself.
    *)
   let run_openstack_command_capture_json args =
-    let cmd = [ "openstack" ] @ extra_args @ args in
+    let cmd = [ openstack_binary ] @ extra_args @ args in
 
     let json, chan = Filename.open_temp_file "v2vopenstack" ".json" in
     unlink_on_exit json;
@@ -353,6 +363,9 @@ object
   inherit output
 
   method precheck () =
+    (* Check the openstack command exists. *)
+    error_unless_openstack_command_exists ();
+
     (* Run the openstack command simply to check we can connect
      * with the provided authentication parameters/environment
      * variables.  Issuing a token should have only a tiny

v2v/virt-v2v-output-openstack.pod

@@ -54,6 +54,9 @@ The reason for this is because to create Cinder volumes that will
 contain the guest data (for the converted guest) we must attach those
 Cinder volumes to an OpenStack virtual machine.
 
+The C<openstack> command must be installed in the appliance.  We use
+it for communicating with OpenStack.
+
 When virt-v2v is running in the conversion appliance, you must supply
 the name or UUID of the conversion appliance to virt-v2v, eg:
 
@@ -206,7 +209,8 @@ leave the system disk in Glance, and import the data disks to Cinder.
 
 =head1 SEE ALSO
 
-L<virt-v2v(1)>.
+L<virt-v2v(1)>,
+L<https://docs.openstack.org/python-openstackclient/latest/cli/man/openstack.html>.
 
 =head1 AUTHOR