builder: Create an install log file, and dump the full log on error.

This should make debugging much simpler, and also provides a
build log in the guest once it's built.

builder/builder.ml

@@ -43,7 +43,7 @@ let mode, arg,
   firstboot, run,
   format, gpg, hostname, install, list_long, network, output,
   password_crypto, quiet, root_password,
-  size, source, upload =
+  size, source, upload, wipe_logfile =
   let display_version () =
     let g = new G.guestfs () in
     let version = g#version () in
@@ -163,6 +163,8 @@ let mode, arg,
     upload := (file, dest) :: !upload
   in
 
+  let wipe_logfile = ref false in
+
   let ditto = " -\"-" in
   let argspec = Arg.align [
     "--attach",  Arg.String attach_disk,    "iso" ^ " " ^ s_"Attach data disk/ISO during install";
@@ -194,6 +196,7 @@ let mode, arg,
     "-l",        Arg.Unit list_mode,        " " ^ s_"List available templates";
     "--list",    Arg.Unit list_mode,        ditto;
     "--long",    Arg.Set list_long,         ditto;
+    "--no-logfile", Arg.Set wipe_logfile,   " " ^ s_"Wipe build log file";
     "--long-options", Arg.Unit display_long_options, " " ^ s_"List long options";
     "--network", Arg.Set network,           " " ^ s_"Enable appliance network (default)";
     "--no-network", Arg.Clear network,      " " ^ s_"Disable appliance network";
@@ -252,6 +255,7 @@ read the man page virt-builder(1).
   let size = !size in
   let source = !source in
   let upload = List.rev !upload in
+  let wipe_logfile = !wipe_logfile in
 
   (* Check options. *)
   let arg =
@@ -296,7 +300,7 @@ read the man page virt-builder(1).
   firstboot, run,
   format, gpg, hostname, install, list_long, network, output,
   password_crypto, quiet, root_password,
-  size, source, upload
+  size, source, upload, wipe_logfile
 
 (* Timestamped messages in ordinary, non-debug non-quiet mode. *)
 let msg fs = make_message_function ~quiet fs
@@ -635,11 +639,21 @@ let () =
   | _ ->
     eprintf (f_"%s: warning: root password could not be set for this type of guest\n%!") prog
 
+(* Based on the guest type, choose a log file location. *)
+let logfile =
+  match g#inspect_get_type root with
+  | "windows" | "dos" ->
+    if g#is_dir "/Temp" then "/Temp/builder.log" else "/builder.log"
+  | _ ->
+    if g#is_dir "/tmp" then "/tmp/builder.log" else "/builder.log"
+
 (* Useful wrapper for scripts. *)
-let do_run cmd =
+let do_run ~display cmd =
   (* Add a prologue to the scripts:
    * - Pass environment variables through from the host.
-   * - Send stdout to stderr so we capture all output in error messages.
+   * - Send stdout and stderr to a log file so we capture all output
+   *   in error messages.
+   * Also catch errors and dump the log file completely on error.
    *)
   let env_vars =
     filter_map (
@@ -650,13 +664,22 @@ let do_run cmd =
   let env_vars = String.concat "\n" env_vars ^ "\n" in
 
   let cmd = sprintf "\
-exec 1>&2
+exec >>%s 2>&1
 %s
 %s
-" env_vars cmd in
+" (quote logfile) env_vars cmd in
 
-  if debug then eprintf "running: %s\n%!" cmd;
-  ignore (g#sh cmd)
+  if debug then eprintf "running command:\n%s\n%!" cmd;
+  try ignore (g#sh cmd)
+  with Guestfs.Error msg ->
+    (* Cat the log file. *)
+    (try g#download logfile "/dev/stderr"
+     with exn ->
+       eprintf (f_"%s: internal error: could not display the log file: %s\n")
+         prog (Printexc.to_string exn)
+    );
+    eprintf (f_"%s: %s: command exited with an error\n") prog display;
+    exit 1
 
 let guest_install_command packages =
   let quoted_args = String.concat " " (List.map quote packages) in
@@ -689,7 +712,7 @@ let () =
     msg (f_"Installing packages: %s") (String.concat " " install);
 
     let cmd = guest_install_command install in
-    do_run cmd;
+    do_run ~display:cmd cmd
   )
 
 (* Upload files. *)
@@ -729,12 +752,22 @@ let () =
     | `Script script ->
       msg (f_"Running: %s") script;
       let cmd = read_whole_file script in
-      do_run cmd
+      do_run ~display:script cmd
     | `Command cmd ->
       msg (f_"Running: %s") cmd;
-      do_run cmd
+      do_run ~display:cmd cmd
   ) run
 
+(* Wipe the log file. *)
+let () =
+  if wipe_logfile && g#exists logfile then (
+    msg (f_"Wiping the log file");
+
+    (* Try various methods with decreasing complexity. *)
+    try g#scrub_file logfile
+    with _ -> g#rm_f logfile
+  )
+
 (* Unmount everything and we're done! *)
 let () =
   msg (f_"Finishing off");

builder/virt-builder.pod

@@ -310,6 +310,14 @@ each operating system option.
 
 See also: I<--source>, L</CREATING YOUR OWN TEMPLATES>.
 
+=item B<--no-logfile>
+
+Wipe C<builder.log> (log file from build commands) from the image
+after building is complete.  If you don't want to reveal precisely how
+the image was built, use this option.
+
+See also: L</LOG FILE>.
+
 =item B<--network>
 
 =item B<--no-network>
@@ -569,6 +577,31 @@ The above command will create an C<rjones> account with no password,
 and force the user to set a password when they first log in.  There
 are other ways to manage passwords, see L<useradd(8)> for details.
 
+=head2 LOG FILE
+
+Scripts and package installation that runs at build time (I<--run>,
+I<--run-command>, I<--install>, but I<not> firstboot) is logged in one
+of the following locations:
+
+=over 4
+
+=item C</tmp/builder.log>
+
+On Linux, BSD and other guests.
+
+=item C<C:\Temp\builder.log>
+
+On Windows, DOS guests.
+
+=item C</builder.log>
+
+If C</tmp> or C<C:\Temp> is missing.
+
+=back
+
+If you don't want the log file to appear in the final image, then
+use the I<--no-logfile> command line option.
+
 =head2 INSTALLATION PROCESS
 
 When you invoke virt-builder, installation proceeds as follows: