On Sun 04 Dec 2011 03:45:10 AM EST, Ayal Baron wrote: > > > ----- Original Message ----- >> On Sat, Dec 03, 2011 at 06:08:45PM -0500, Ayal Baron wrote: >>> >>> >>> ----- Original Message ----- >>>> On Thu, Dec 01, 2011 at 10:13:53PM -0500, Saggi Mizrahi wrote: >>>>> I want to suggest a different way of handling constants.py and >>>>> config.py >>>>> the current way is clumsy and makes making convoluted code >>>>> easy. >>>>> >>>>> GLOBAL VARIABLES ARE BAD. It's not something I invented. It's >>>>> well >>>>> accepted that proper scoping yields better code. >>>> >>>> FOLLOWING UPERCASE MAXIMS BLINDLY IS BAD. (and that's something I >>>> have invented.) >>>> >>>>> >>>>> The way we use those two files shows how much of a mess >>>>> globally >>>>> accessible variable can be. >>>>> >>>>> Not putting paths to executable in constants.py >>>>> ----------------------------------------------- >>>>> Instead we should have a module for each utility executable. >>>>> The >>>>> module >>>>> should wrap the utility with a pythonic interface. That way >>>>> there >>>>> is no >>>>> reason for more then one module to have access to a utility's >>>>> path. >>>>> >>>>> For example: >>>>> >>>>> cat.py >>>>> ------ >>>>> >>>>> _CAT_PATH = @CAT_PATH@ >>>>> >>>>> def cat(files): >>>>> cmd = [_CAT_PATH] + files >>>>> out, err = exec(cmd) >>>>> return out >>>>> >>>>> Now there is no need to know where cat is. You have a proper >>>>> interface >>>>> to use. Preventing people from re-wrapping the utility over and >>>>> over. >>>>> This in turn means you have a canonical wrapper that is more >>>>> likely >>>>> to work. >>>> >>>> I agree that our current behavior is clunky. Most external >>>> executable >>>> should be >>>> wrapped by functions that exposes the functionality which we need >>>> from them. >>>> >>>> I am not sure that having a module per executable makes the most >>>> sense; I'd >>>> separate modularity based on Vdsm usage of them. Anyway, the only >>>> up >>>> side of our >>>> current constants-aggregating approach, is that the number of >>>> files >>>> editted by >>>> autoconf is limitted. >>>> >>>> P.S. EXT_CAT is a horrible example. It exists only for letting >>>> Vdsm >>>> read >>>> /etc/multipath.conf. This functionality must be wrapped properly >>>> and >>>> shoved into >>>> supervdsm. >>> >>> That doesn't mean that supervdsm shouldn't have a canonical way of >>> using it which could be later on leveraged in other places. >>> i.e. assuming we converge on this way of doing things, it should >>> apply to supervdsm as well. >> >> I'm not sure what you are saying here... >> But I would like to stress again that "cat" is way too low-level and >> generic to be exposed by supervdsm. supervdsm should expose >> higher-level >> functions that cannot harm irrelevant parts of the host. > > You are 100% correct. What I'm saying is that when *supervdsm* uses cat, it > should do so like above. > The API it exposes should not include a generic 'cat', no doubt about that. > >> >> Dan. >>
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