linux-kernel - Re: CONFIG_VFAT_FS

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Date:	Fri, 3 Jul 2009 13:25:47 +1000
From:	tridge@...ba.org
To:	Jan Engelhardt <jengelh@...ozas.de>
Cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Theodore Tso <tytso@....edu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Pavel Machek <pavel@....cz>, john.lanza@...ux.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>, corbet@....net,
	jcm@...masters.org
Subject: Re: CONFIG_VFAT_FS_DUALNAMES regressions

Hi Jan,

 > No-no, as previously mentioned it ignores filenames not in the
 > format of dscf????.jpg. But if I interpret the hexdump right,
 > standard Linux creates a long name *anyway*, even for names
 > fitting in 8.3, if it's lowercase:
 > 
 > .$,2 "00bce510 79 39 79 39 03 00 f5 5b-79 39 95 4b 00 00 00 00 |y9y9? ?[y9?K    |    
 > .$,2 "00bce520 41 67 00 6f 00 64 00 64-00 61 00 0f 00 27 6d 00 |Ag o d d a ? 'm |    
 > .$,2 "00bce530 6e 00 2e 00 7a 00 69 00-70 00 00 00 00 00 ff ff |n . z i p     ??|    
 > .$,2 "00bce540 47 4f 44 44 41 4d 4e 20-5a 49 50 20 00 64 d2 20 |GODDAMN ZIP  d? |    

right, that is not unexpected. It creates both the long name and the
short name in this case as the short name is constrained to not be
case preserving, and the filesystem normally tries to be both
case-insensitive and case-preserving. As the long name has no
constraints on the case of characters it creates both so that devices
(like your camera I think) that only look at the 8.3 entries will see
a file.

That is why setting shortname=winnt is desirable when using the "no
dualnames" patch I posted. That tells Linux to behave more like what
current windows versions behave, which is to try and put it in the 8.3
entry if it can, even if it is all lowercase.

What I would like to see us do for maximum compatibility with devices
like this, while still maximising the legal safety, is to take mixed
case prefixes or suffixes that fit in 8.3 and uppercase them and set
the CASE_LOWER_BASE and CASE_LOWER_EXT bits appropriately in the flags
field, and not store a long name. That would makes us really nicely
compatible with devices like your camera, at the price of losing mixed
case preservation for 8.3 names.

It would be another departure from previous behaviour however, so I
want to get some feedback from Hirofumi-san first. 

btw, if you still think your camera really is looking at the long
filename entries, then try creating a file like DsCf2000.jpg with a
unpatched kernel, mounted with shortname=winnt. That will create two
directory entries for the file, one being DSCF2000.JPG and the other
being DsCf2000.jpg.

Then view the list of photos on the LCD back panel of your
camera. Assuming it has a way to see the filename, does it display the
mixed case name DsCf2000.jpg, or does it display a non-mixed name like
dscf2000.jpg or DSCF2000.JPG.

If it displays a mixed name (ie. DsCf) then your camera can indeed
read long filename entries. If it displays a all uppercase or all
lowercase name then I think it is only capable of reading short names
from FAT filesystems. That is what I think you will find.

Cheers, Tridge
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