On 12/03/2012 02:46 PM, Roald van Loon wrote:
On Mon, Dec 3, 2012 at 10:51 PM, Josh Durgin <josh.durgin@xxxxxxxxxxx> wrote:
It looks like you've got a good start on integrating it into the main
ceph infrastructure. Skimming over it, the general structure makes sense
to me. One part that might be a bit tricky is making the new parsing
backwards compatible with the old parsing.
1) For config options in general, '-', '_', and ' ' are all equivalent.
2) In ceph's config file format, we treat ';' as a comment in addition to
'#'.
I'm not sure how difficult those are to handle with the built-in
boost::program_options parsers.
Well, there is another (maybe larger) problem; metavalues. Boost::po
can't handle them. That's why I am implementing the raw config file
parsing separately (partly using boost::property_tree actually), load
all options in a tree hierarchy (for example [osd.1] -> [osd] ->
[global]) and then do metavalue lookups top-down with static regexps.
Then, I have a parsed and complete set in the top of the tree (osd.1
in this case) which I can feed to boost::po to be parsed. Still have
to work out some of the details though, but I think this is generally
a nice way of config parsing. I'll see if I can find the time this
week to implement it if you're interested.
I think this makes sense. I guess the alternative is expanding the
metavalues after boost::po breaks them down, but I don't see any
big advantages either way.
Converting some of the individual command line tools that use
subcommands might be a little cumbersome too, but I think they'll
be better off once it's done.
My biggest concern is that most code directly accesses members of
md_config_t by means of g_conf->foo. It's very difficult to port that
to the new class without actually loading all of the available config
options as class members - something I'm personally not a big fan of.
I haven't had the time to think of a nice solution, yet (something
like getter/setter methods maybe, or macros?). If you have any
thoughts about this I'd very much like to hear them.
I'm not sure this is the best solution, but we have a small number of
types of config values. We could have a getter for each type (like
md_config_t::get_val(), but nicer to use in C++ and asserting that
the configuration option is valid and of the appropriate type), i.e.:
uint64_t get_uint64_t(const std::string &name);
This could work for internal users (i.e. anyone using g_conf->foo right
now). The library users (e.g. rados_conf_get()) would still want an
interface like md_config_t::get_val() that returns an error if the
option doesn't exist.
Josh
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