[augeas-devel] [Matahari] Augeas-based configuration agent

[David Lutterkort]

On Wed, 2011-05-11 at 09:24 +0200, Radek Novacek wrote:
> (resended as I wasn't member of augeas-devel mailing list)
> 
> > I was hoping somebody would just cook up a patch based on augtool ;) It
> > shouldn't be much more work than doing it (yet again) for standalone
> > use.
> 
> I can try to do it. To be clear, the task is to add method to augeas library 
> called e.g. batch, which takes string argument. In this argument will be 
> command (or semicolon separated list of commands) same as for augtool. What 
> will the method return? True only if all commands succeeds, false otherwise?

All good questions; I initially thought we could just take parts of
augtool.c (roughly run_command and everything it depends on) and put it
behind the API. One of my goals here is that augtool can use this new
API, without any changes in its behavior.

Besides how to indicate errors, the other question is how to deal with
all the printing to stdout and stderr that the various cmd_* handlers in
augtool.c do right now. One option would be to let the caller pass in
file pointers for that.

I am thinking we should add two functions to the API:

        int aug_srun(augeas *aug,
                     const char *text, size_t text_len,
                     FILE *out, unsigned int flags)
        
and

        int aug_frun(augeas *aug,
                     FILE *in, FILE *out,
                     unsigned int flags)
        
The functions return 0 on success and -1 on error; further details about
the error can be found with aug_error; if that returns AUG_ECOMMAND,
something went wrong with parsing a command. We can use
aug_error_minor_message and aug_error_details to provide more error
information.

The commands are either read from TEXT (aug_srun) or from IN (aug_frun,
reads till EOF); commands must be separated by newlines. I don't think
there's any point in getting fancy with semicolons.

If OUT is non-NULL, commands that produce output (e.g.
'get /augeas/version' or 'print /files/etc/hosts') will print that on
OUT. That way, augtool can just pass stdout and the user should see
output identical to the current output.

By default, executing commands is aborted when an error is encountered;
by setting FLAGS to AUG_RUN_CONTINUE, errors are ignored as much as
possible (e.g., a syntax error will be ignored, but an OOM would still
lead to returning with an error)

How does all that sound ? Since this now seems a little more involved
than I first thought, I might have a crack at it tomorrow. Please let me
know if the suggested API's would work for you.

David