Re: [PATCH v8 02/13] exfat: add super block operations

From: "Pali Rohár" <pali.rohar@gmail.com>
To: Namjae Jeon <namjae.jeon@samsung.com>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	gregkh@linuxfoundation.org, valdis.kletnieks@vt.edu, hch@lst.de,
	sj1557.seo@samsung.com, linkinjeon@gmail.com
Subject: Re: [PATCH v8 02/13] exfat: add super block operations
Date: Thu, 2 Jan 2020 09:30:29 +0100	[thread overview]
Message-ID: <20200102083029.uv2gtig3ski23dpe@pali> (raw)
In-Reply-To: <000701d5c132$bed73c80$3c85b580$@samsung.com>

On Thursday 02 January 2020 15:06:16 Namjae Jeon wrote:
> > > +static const struct fs_parameter_spec exfat_param_specs[] = {
> > > +	fsparam_u32("uid",			Opt_uid),
> > > +	fsparam_u32("gid",			Opt_gid),
> > > +	fsparam_u32oct("umask",			Opt_umask),
> > > +	fsparam_u32oct("dmask",			Opt_dmask),
> > > +	fsparam_u32oct("fmask",			Opt_fmask),
> > > +	fsparam_u32oct("allow_utime",		Opt_allow_utime),
> > > +	fsparam_string("iocharset",		Opt_charset),
> > > +	fsparam_flag("utf8",			Opt_utf8),
> > 
> > Hello! What is the purpose of having extra special "utf8" mount option?
> > Is not one "iocharset=utf8" option enough?
> utf8 nls_table supports utf8<->utf32 conversion and does not support
> surrogate character conversion.

So in other words, this is just subset of UTF-8 just to 3 byte long
sequences (for Unicode code points up to the U+FFFF).

> The utf8 option can support the surrogate
> character conversion of utf16 using utf16s_to_utf8s/utf8s_to_utf16s of
> the nls base.

So this is full UTF-8 support, right?

And what is the point to have two options for UTF-8 support, when one is
incomplete / broken? I see no benefit to have first option at all.
Providing incomplete / broken support to userspace does not make much
sense if we already have full and working support via different mount
option. Maybe second option with full UTF-8 support should be used also
by iocharset=utf8 and then we do not need utf8 option at all?

-- 
Pali Rohár
pali.rohar@gmail.com