linux-ext4 - Re: [PATCH 02/17] ext4: Add fs parameter description

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Date:   Tue, 24 Dec 2019 17:18:18 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Lukas Czerner <lczerner@...hat.com>
Cc:     linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 02/17] ext4: Add fs parameter description

On Tue, Dec 17, 2019 at 05:34:32PM +0100, Lukas Czerner wrote:

> > If so, I would prefer
> > 	fsparam_flag_no("barrier", Opt_barrier),	// barrier | nobarrier
> > 	fsparam_u32("barrier", Opt_barrier),		// barrier=<number>
> > as the solution, with fs_parse() having been taught to allow argument-bearing
> > and argument-less options with the same name, picking the right one.  That
> > way Opt_nobarrier gets removed as well...
> > 
> > I'll push a branch with that stuff later today; will post when it's out...
> 
> That would be great, thanks.

It took longer than I hoped, sorry ;-/  The current patchset is in
#untested.fs_parse; the really interesting part is up to
"turn fs_param_is_... into functions".

One surprising source of PITA around your patchset is ext4_show_options().
It pretty much forces you into keeping "no..." forms separate, even though
normally you could just say
	fsparam_flag_no("quota",               Opt_quota),
and get rid of Opt_noquota, etc.

If you keep that dependency, it'll need to be documented - right in
fs/ext4/super.c, to make sure we don't get "optimizing" followups breaking
the hell out of things.

Said that, I really doubt that token2str() is a good idea.  It might make
more sense to start with separating _ext4_show_options() from that
machinery.

Another thing is that all fsparam_bool() users are modifying user-visible
ABI; use fparam_flag_no() + fsparam_u32() with the same name and same
opt - that'll give you the existing behaviour.