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README
REAMDE for the Erlang bindings to libguestfs
----------------------------------------------------------------------

To get started, take a look at the man page guestfs-erlang(3) and the
example programs.

Note that to run the examples, the "erl-guestfs" binary must be on the
path.  To run the examples without installing, do:

 cd erlang
 PATH=.:$PATH ../run ./examples/create_disk.erl
 PATH=.:$PATH ../run ./examples/inspect_vm.erl /path/to/vm_disk.img

To simplify the implementation we currently don't support events or
user cancellation.  However it would be pretty simple to add both of
these.  Patches welcome!

Implementation notes
----------------------------------------------------------------------

These bindings are done using a port that launches an external
program, following this example:
http://www.erlang.org/doc/tutorial/erl_interface.html

The reason for this is that the libguestfs API is synchronous and
calls may take a long time.  If we used a linked-in driver then that
would require us to start a POSIX thread in the Erlang interpreter and
manage concurrency issues.  Using an external process per handle
simplifies the implementation and makes it much less likely to break
the Erlang interpreter.

The external C program is called "erl-guestfs".  It is normally
installed in $(bindir), eg. /usr/bin/erl-guestfs.

You need to make sure that the Erlang code and erl-guestfs are the
same version.  The protocol used between the Erlang code (guestfs.erl)
and erl-guestfs might change in future versions.

There is not really any type checking done in the erl-guestfs binary,
which means you can get undefined behaviour if you send incorrect
argument types.  Patches welcome to improve this situation.

Licensing
----------------------------------------------------------------------

Because the C program runs in a separate process, it is licensed as
GPLv2+.  The Erlang part which "links" into the Erlang interpreter is
licensed as LGPLv2+.  We believe this means there is no impediment to
using libguestfs from closed source Erlang programs.

The example programs are under a separate, very permissive license,
which basically allows you to do what you want with them.  See
erlang/examples/LICENSE.
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