Re: [PATCH 02/12] fs_parse: fix fs_param_v_optional handling

[Al Viro <viro@zeniv.linux.org.uk>]

On Tue, Dec 17, 2019 at 01:18:13AM +0000, Al Viro wrote:

> So how about a flag for "takes no arguments", set automatically by
> fsparam_flag()/fsparam_flag_no(), with fs_lookup_key() taking an
> extra "comes with argument" flag and filtering according to it?
> Rules:
> 	foo		=> "foo", true
> 	foo=		=> "foo", false
> 	foo=bar		=> "foo", false
> And to hell with the "optional" flag; for gfs2 we'd end up with
> 	fsparam_flag_no("quota", Opt_quota_flag),			// quota|noquota
> 	fsparam_flag_enum("quota", Opt_quota, gfs2_param_quota),	// quota={on|account|off}
> Postprocessing won't be any harder, really - we could bloody well do
> 	case Opt_quota_flag:
> 		result.int_32 = result.negated ? GFS2_QUOTA_OFF : GFS2_QUOTA_ON;
> 		/* fallthru */
> 	case Opt_quota:
> 		args->ar_quota = result.int_32;
>                 break;
> with gfs2_param_quota having the right values in it, instead of
> that intermediate enum.
> 
> All ->has_value checks go away that way, AFAICS.  With minimal
> impact on yet-to-be-merged series...

FWIW, we have the following types right now:
fs_param_is_flag	no argument
fs_param_is_bool	no argument or string argument (1 instance in mainline[*])
fs_param_is_u32		string argument [**]
fs_param_is_u32_octal	string argument
fs_param_is_u32_hex	string argument
fs_param_is_s32		string argument
fs_param_is_u64		string argument
fs_param_is_enum	string argument; gfs2 has the quota/noquota/quota=... mess
fs_param_is_string	string argument; ceph (and nfs) have fsc/nofsc/fsc=...
fs_param_is_fd		unused at the moment; eventually - string argument.
fs_param_is_blob	fsconfig-only
fs_param_is_blockdev	fsconfig-only
fs_param_is_path	fsconfig-only

[*] no_disconnect in gadgetfs; buggered, since it used to require a numeric
argument.  Now it quietly treats no_disconnect as no_disconnect=1 and
rejects e.g. no_disconnect=2.  There are two more in ext4, also buggered
as far as I can tell.
[**] ext4 has init_itable/init_itable=%u/noinit_itable

The total over all filesystems with conversions posted or already in mainline:

* no_disconnect [drivers/usb/gadget/function/f_fs.c, broken]
* init_itable/init_itable=%u/noinit_itable [ext4]
* fsc/fsc=%s/nofsc [ceph]
* fsc/fsc=%s/nofsc [nfs]
* quota/quota=on/quota=off/quota=account/noquota [gfs2]
* barrier/barrier=%u/nobarrier [ext4]
* auto_da_alloc/auto_da_alloc=%u/noauto_da_alloc [ext4]

It's rare.  So much that I don't believe that fs_param_v_optional has any
reason to exist.  Let's split those entries and be done with that.

Hmm...  Deciding whether we have an argument-bearing or no-argument case
is somewhat inconvenient for fsconfig-generated calls - check for
NULL param->string is, strictly speaking, in nasal daemon territory
for types other than flag and string...  OK, sold - let's check for
fs_value_is_flag.  So I'm combining your patch with #9/12 (to avoid bisect
hazard) + correction for rbd.  And putting that in the very beginning of
fs_parser reorg series, with elimination of fs_param_v_optional closer
to the end.