linux-kernel - Re: CIFS: Rename bug on servers not supporting inode numbers

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Date:	Thu, 24 Nov 2011 06:08:29 +0100
From:	Günter Kukkukk <linux@...kukk.com>
To:	samba-technical@...ts.samba.org
Cc:	Amit Sahrawat <amit.sahrawat83@...il.com>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-cifs@...r.kernel.org, NamJae Jeon <linkinjeon@...il.com>,
	Jeff Layton <jlayton@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Steve French <sfrench@...ba.org>,
	Steve French <smfrench@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	ashishsangwan2@...il.com, akpm@...ux-foundation.org,
	Anton Altaparmakov <aia21@....ac.uk>,
	Unix Support <unix-support@....cam.ac.uk>
Subject: Re: CIFS: Rename bug on servers not supporting inode numbers

On Wednesday 23 November 2011 19:00:16 Amit Sahrawat wrote:
> Hi Alan,
> Ok, translations cannot be added easily. But any idea why surrogate
> pairs are not handled? I think handling for surrogate pairs can be
> added by identifying proper points(there are not many I guess). Please
> share your views.
> 
> Regards,
> Amit Sahrawat
> 
> On Wed, Nov 23, 2011 at 10:42 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
> > On Wed, 23 Nov 2011 11:31:47 -0500 (EST)
> > 
> > Alan Stern <stern@...land.harvard.edu> wrote:
> >> On Wed, 23 Nov 2011, NamJae Jeon wrote:
> >> > Hi. Alan.
> >> > Would you know why there is no upper/lower case table in nls utf8 ?
> >> > And Currently Surrogate pair is not supported also in nls utf8. Is
> >> > there the reason ?
> >> 
> >> I don't know.
> > 
> > For one case translations are locale specific and very very complicated.
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel"
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> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/

"Surrogate pairs" had to been implemented to extend the former
16 bit limit of UCS-2/UTF-16.

Unicode has been limited to max 0x0010FFFF glyphs - which
would not fit in UCS-2/UTF-16.

To extend UTF-16, the "surrogate range" between D800 and DFFF was "stolen" 
from the one of the previously named "Private Use Areas" of UCS-2.
-----

Have those "surrogate pairs" any impact on _todays_ linux file name conventions?

I think the easy answer is NO !

AFAIK - _no_ current operating system is supporting this!

We are talking here about "allowed dir/file name characters"!

The main reason behind "Surrogate pairs" was to allow "userland" (!)
applications to use worldwide special character glyphs!
---------

Anyway - in nls_base.c
.....
static const struct utf8_table utf8_table[] =
{
    {0x80,  0x00,   0*6,    0x7F,           0,         /* 1 byte sequence */},
    {0xE0,  0xC0,   1*6,    0x7FF,          0x80,      /* 2 byte sequence */},
    {0xF0,  0xE0,   2*6,    0xFFFF,         0x800,     /* 3 byte sequence */},
    {0xF8,  0xF0,   3*6,    0x1FFFFF,       0x10000,   /* 4 byte sequence */},
    {0xFC,  0xF8,   4*6,    0x3FFFFFF,      0x200000,  /* 5 byte sequence */},
    {0xFE,  0xFC,   5*6,    0x7FFFFFFF,     0x4000000, /* 6 byte sequence */},
    {0,						       /* end of table    */}
};
........
that configured range exceeds the max. allowed unicode range 0x0010FFFF
and _must_ be changed to:

static const struct utf8_table utf8_table[] =
{
    {0x80,  0x00,   0*6,    0x7F,           0,         /* 1 byte sequence */},
    {0xE0,  0xC0,   1*6,    0x7FF,          0x80,      /* 2 byte sequence */},
    {0xF0,  0xE0,   2*6,    0xFFFF,         0x800,     /* 3 byte sequence */},
    {0xF8,  0xF0,   3*6,    0x1FFFFF,       0x10000,   /* 4 byte sequence */},
    {0,						       /* end of table    */}
};

Cheers, Günter
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