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The previously library-side ‘file_architecture’ API is reimplemented in the daemon, in OCaml. There are some significant differences compared to the C implementation: - The C code used libmagic. That is replaced by calling the ‘file’ command (because that is simpler than using the library). - The C code had extra cases to deal with compressed files. This is not necessary since the ‘file’ command supports the ‘-z’ option which transparently looks inside compressed content (this is a consequence of the change above). This commit demonstrates a number of techniques which will be useful for moving inspection code to the daemon: - Moving an API from the C library to the OCaml daemon. - Calling from one OCaml API inside the daemon to another (from ‘Filearch.file_architecture’ to ‘File.file’). This can be done and is done with C daemon APIs but correct reply_with_error handling is more difficult in C. - Use of Str for regular expression matching within the appliance.
This program generates a large amount of code and documentation for all the daemon actions. To add a new action there are only two files you need to change, 'actions_*.ml' to describe the interface, and daemon/<somefile>.c to write the implementation. After editing these files, build it (make -C generator) to regenerate all the output files. 'make' will rerun this automatically when necessary. IMPORTANT: This program should NOT print any warnings at compile time or run time. If it prints warnings, you should treat them as errors. OCaml tips: (1) In emacs, install tuareg-mode to display and format OCaml code correctly. 'vim' comes with a good OCaml editing mode by default. (2) Read the resources at http://ocaml.org/learn/ (3) A module called 'Foo' is defined in one or two files called 'foo.mli' and 'foo.ml' (NB: lowercase first letter). The *.mli file, if present, defines the public interface for the module. The *.ml file is the implementation. If the *.mli file is missing then everything is exported. Some notable files in this directory: actions_*.ml The libguestfs API. proc_nr.ml Procedure numbers associated with each API. structs.ml Structures returned by the API. c.ml Generate C API. <lang>.ml Generate bindings for <lang>. main.ml The main generator program. Note about long descriptions: When referring to another action, use the format C<guestfs_other> (ie. the full name of the C function). This will be replaced as appropriate in other language bindings. Apart from that, long descriptions are just perldoc paragraphs. Note about extending functions: In general you cannot change the name, number of required arguments or type of required arguments of a function, since this would break backwards compatibility. You may add another optional argument, *if* the function has >= 1 optional arguments already. Add it at the end of the list. You may add optional arguments to a function that doesn't have any. However you *must* set the once_had_no_optargs flag to true, so that the relevant backwards compatibility bindings can be added.