Re: [PATCH v3 2/4] 9p: Add mount option for negative dentry cache retention

[Dominique Martinet <asmadeus@codewreck.org>]

Christian Schoenebeck wrote on Tue, Mar 03, 2026 at 03:53:47PM +0100:
> > +	fsparam_string	("source",		Opt_source),
> > +	fsparam_u32hex	("debug",		Opt_debug),
> > +	fsparam_uid	("dfltuid",		Opt_dfltuid),
> > +	fsparam_gid	("dfltgid",		Opt_dfltgid),
> > +	fsparam_u32	("afid",		Opt_afid),
> > +	fsparam_string	("uname",		Opt_uname),
> > +	fsparam_string	("aname",		Opt_remotename),
> > +	fsparam_flag	("nodevmap",		Opt_nodevmap),
> > +	fsparam_flag	("noxattr",		Opt_noxattr),
> > +	fsparam_flag	("directio",		Opt_directio),
> > +	fsparam_flag	("ignoreqv",		Opt_ignoreqv),
> > +	fsparam_string	("cache",		Opt_cache),
> > +	fsparam_string	("cachetag",		Opt_cachetag),
> > +	fsparam_string	("access",		Opt_access),
> > +	fsparam_flag	("posixacl",		Opt_posixacl),
> > +	fsparam_u32	("locktimeout",		Opt_locktimeout),
> > +	fsparam_flag	("ndentrycache",	Opt_ndentrycache),
> > +	fsparam_u32	("ndentrycache",	Opt_ndentrycachetmo),
> 
> That double entry is surprising. So this mount option is supposed to be used
> like ndentrycache=n for a specific timeout value (in ms) and just ndentrycache
> (without any assignment) for infinite timeout. That's a bit weird.

Could make it a s32 and say <0 means infinite? I think we have that
somewhere

> Documentation/filesystems/9p.rst should be updated as well BTW.
> 
> Nevertheless, like mentioned before, I really think the string "timeout"
> should be used, at least in a user visible mount option. Keep in mind that
> timeouts are a common issue to look at, so it is common to just grep for
> "timeout" in a code base or documentation. An abbrevation like "tmo" or
> leaving it out entirely is for me therefore IMHO inappropriate.
> 
> You found "ndentrycachetimeout" too horribly long, or was that again just
> motivated by the code indention below? I personally find those indention
> alignments completely irrelevant, not sure how Dominique sees that.
> Personally I avoid them, as they cost unnecessary time on git blame.

I rarely use blame at all and it's possible to ignore whitespaces for
blame, but I'd tend to agree here, I don't care if this stays aligned.

OTOH ndentrycachetimeout as a mount option is a mouthful,
negativetimeout or negtimeout sounds clear enough to me?
I can't think of anything else that'd be negative related
to timeouts, but perhaps it's the lack of sleep speaking

-- 
Dominique Martinet | Asmadeus