libguestfs/HACKING

PLEASE LOOK AT THE TOP OF EACH FILE BEFORE EDITING TO SEE WHETHER IT
IS AUTOMATICALLY GENERATED OR NOT.

Adding a new action
----------------------------------------------------------------------

All action functions are generated automatically, so there are only
two files you need to edit:

(1) src/generator.ml: Add your new action, parameters, description,
etc. to the big list called 'functions' at the top of this file.

(2) Edit/create a C file in daemon/ subdirectory which implements your
'do_action' function.  Take a look at one of the numerous examples
there.

Formatting
----------------------------------------------------------------------

Try to use GNU / Emacs default formatting, following the convention
used elsewhere in the source.

Please make sure that the code compiles without warnings.

Please test any changes.

Useful targets:
  make syntax-check    Checks the syntax of the C code.
  make check           Runs the test suite.

Enable warnings, and fix any you find:
  ./configure --enable-gcc-warnings

Code indentation
----------------------------------------------------------------------
Our C source code generally adheres to some basic code-formatting
conventions.  The existing code base is not totally consistent on this
front, but we do prefer that contributed code be formatted similarly.
In short, use spaces-not-TABs for indentation, use 2 spaces for each
indentation level, and other than that, follow the K&R style.

If you use Emacs, add the following to one of one of your start-up files
(e.g., ~/.emacs), to help ensure that you get indentation right:

  ;;; In libguestfs, indent with spaces everywhere (not TABs).
  ;;; Exceptions: Makefile and ChangeLog modes.
  (add-hook 'find-file-hook
      '(lambda () (if (and buffer-file-name
                           (string-match "/libguestfs\\>" (buffer-file-name))
                           (not (string-equal mode-name "Change Log"))
                           (not (string-equal mode-name "Makefile")))
                      (setq indent-tabs-mode nil))))

  ;;; When editing C sources in libguestfs, use this style.
  (defun libguestfs-c-mode ()
    "C mode with adjusted defaults for use with libguestfs."
    (interactive)
    (c-set-style "K&R")
    (setq c-indent-level 2)
    (setq c-basic-offset 2))
  (add-hook 'c-mode-hook
            '(lambda () (if (string-match "/libguestfs\\>" (buffer-file-name))
                            (libguestfs-c-mode))))

Directories
----------------------------------------------------------------------

appliance/
        The qemu appliance, build scripts and so on.

capitests/
        Automated tests of the C API.

contrib/
        Outside contributions, experimental parts.

csharp/
        Experimental C# bindings.

daemon/
        The daemon that runs inside the guest and carries out actions.

examples/
        The examples.

fish/
        Guestfish (the command-line program / shell)

fuse/
        FUSE (userspace filesystem) built on top of libguestfs.

haskell/
        Haskell bindings.

hivex/
        Hive extraction library, for reading Windows Registry files.
        See hivex/README for more details.

images/
        Some guest images to test against.  These are gzipped to save
        space.  You have to unzip them before use.

        Also contains some files used by the test suite.

inspector/
        Virtual machine image inspector (virt-inspector).

java/
        Java bindings.

m4/
        M4 macros used by autoconf.

ocaml/
        OCaml bindings.

po/
        Translations.

perl/
        Perl bindings.

python/
        Python bindings.

regressions/
        Regression tests.

ruby/
        Ruby bindings.

tools/
        Command line tools like virt-cat, virt-df, virt-edit and more.
        In versions <= 1.0.73 these were all in separate directories
        like cat/, df/, edit/, but since then we moved them all into
        one directory to simplify builds.

src/
        Source code to the C library.
        Also contains the crucial generator program.

test-tool/
        Interactive qemu/kernel test tool.

Debugging
----------------------------------------------------------------------

It's a good idea to use guestfish to try out new commands.

Debugging the daemon is a problem because it runs inside a minimal
qemu environment.  However you can print messages from the daemon, and
they will show up if you use 'guestfish -v'.

Patches
----------------------------------------------------------------------

Submit patches to the mailing list:
http://www.redhat.com/mailman/listinfo/libguestfs
and CC to rjones@redhat.com

I18N
----------------------------------------------------------------------

We support i18n (gettext anyhow) in the library.

However many messages come from the daemon, and we don't translate
those at the moment.  One reason is that the appliance generally has
all locale files removed from it, because they take up a lot of space.
So we'd have to readd some of those, as well as copying our PO files
into the appliance.

Debugging messages are never translated, since they are intended for
the programmers.

Extended printf
----------------------------------------------------------------------

In the daemon code we have created custom printf formatters %Q and %R,
which are used to do shell quoting.

%Q => Simple shell quoted string.  Any spaces or other shell characters
      are escaped for you.

%R => Same as %Q except the string is treated as a path which is prefixed
      by the sysroot.

eg.

asprintf (&cmd, "cat %R", path);
==> "cat /sysroot/some\ path\ with\ spaces"

Note: Do NOT use these when you are passing parameters to the
command{,r,v,rv}() functions.  These parameters do NOT need to be
quoted because they are not passed via the shell (instead, straight to
exec).  You probably want to use the sysroot_path() function however.