Re: [Libguestfs] [PATCH] virt-sysprep:add logging feature

On Fri, Apr 06, 2012 at 01:37:33PM +0800, Wanlong Gao wrote: > Hi Rich, > > I tried to implement the logging feature, but I can't though > compiling with this patch now, could you please give me > some comments? > > The error message is below, > --- > ocamlfind ocamlopt -g -warn-error CDEFLMPSUVYZX -package unix -I ../src/.libs -I ../ocaml -c sysprep_operation.ml -o sysprep_operation.cmx > File "sysprep_operation.ml", line 1, characters 0-1: > Error: The implementation sysprep_operation.ml > does not match the interface sysprep_operation.cmi: > Type declarations do not match: > type operation = { > name : string; > pod_description : string; > extra_args : ((Arg.key * Arg.spec * Arg.doc) * string) list; > perform : Guestfs.guestfs -> string -> bool -> flag list; > } > is not included in > type operation = { > name : string; > pod_description : string; > extra_args : ((Arg.key * Arg.spec * Arg.doc) * string) list; > perform : Guestfs.guestfs -> string -> flag list; > } > The types for field perform are not equal. Indeed they are not! The implementation (*.ml) has changed: > - perform : Guestfs.guestfs -> string -> flag list; > + perform : Guestfs.guestfs -> string -> bool -> flag list; but you must make an equivalent change to the interface (in sysprep_operation.mli) -- adding the extra debug flag. May I suggest another way to do this which is a bit more natural. Use a function. Declare it as: type debug_fn = ('a, unit, string, unit) format4 -> 'a type operation = { ... perform : Guestfs.guestfs -> debug:debug_fn -> string -> flag list } Implementations would just do this: let foo_perform g ~debug root = debug "I'm calling foo %s" root; ... The main function does this: let debug fs = ksprintf (fun str -> if show_log then prerr_endline str) fs ... Sysprep_operations.perform_operations ?operations ~debug g root Note that the debug function prints conditionally, based on whether show_log is set or not.

Rich.