Possible bug in FAT dir listing

Gene Smith gds at chartertn.net
Wed Jan 14 08:03:00 CST 2009


Till Straumann wrote:
> Chris Johns wrote:
>> Gene Smith wrote:
>>   
>>> I formatted an MMC card on linux with gparted as FAT16. I copy one file 
>>> to it called freddy.txt I unmount and dump the partition with dd. The 
>>> root directory entry appears like this:
>>> :
>>> 003d5f0: 0000 0000 0000 0000 0000 0000 0000 0000  ................
>>> 003d600: 4166 0072 0065 0064 0064 000f 0055 7900  Af.r.e.d.d...Uy.
>>> 003d610: 2e00 7400 7800 7400 0000 0000 ffff ffff  ..t.x.t.........
>>> 003d620: 4652 4544 4459 2020 5458 5420 0000 9100  FREDDY  TXT ....
>>> 003d630: 2e3a 2d3a 0000 6eb5 2c3a 0300 1300 0000  .:-:..n.,:......
>>> 003d640: 0000 0000 0000 0000 0000 0000 0000 0000  ................
>>> :
>>>
>>> There are two entries. One starts with A and seems to be unicode of some 
>>> sort (32 bytes at 3d600) while the 2nd is conventional ASCII and is 32 
>>> bytes at 3d620.
>>>
>>> When I mount on rtems and do ls in the shell I see this:
>>>
>>> [/mnt] # ls
>>> Af              FREDDY.TXT
>>>
>>> The entry that starts with A shows up as "Af". From what I have read it 
>>> should actually be ignored and not printed because the byte at 3d60b is 
>>> 0x0f. The 0x0f is the file attributes indicating this is a volume label, 
>>> system file, hidden file and read-only. This is a key that it should not 
>>> be displayed. (Why this filename gets put in I don't know. I think 
>>> windows does the same.)
>>>
>>> Both of these sites mention that the attribute flag 0xf means don't show 
>>> the file:
>>> http://www.win.tue.nl/~aeb/linux/fs/fat/fat-1.html
>>> http://home.teleport.com/~brainy/lfn.htm
>>>
>>> This also explains why a volume label shows up as a file in rtems when 
>>> doing ls. It should be ignored too.
>>>
>>> AFAICT, there is no code in the rtems FAT library to ignore files when 
>>> these attribute flags are set. I only see the "directory" attribute 
>>> checked in some places.
>>>
>>>     
>> I think the FAT code is ok 
> Not sure - I vaguely recall encountering a similar problem
> (w/o using your 'ls' command). Could this be related to PR#1273 ?

I think it is related. If I copy in a file with LFN you get several 
entries in the "directory entry" area for that file. All but the one 
with the name e.g., 123456~1.TXT has the attribute 0xf but all show like 
above (with a leading A, I think) and are not hidden when displayed.

This for me is a minor problem. But the only one so far I have been able 
to get a handle on dealing with my MMC cards.

> 
> T.
>> rather I suspect this is a result of the ls 
>> command's handling of the attributes for the directory. Could you please file 
>> a PR with RTEMS bugzilla ? I ported this command from Unix and it must have 
>> some issues.
>>
>> Regards
>> Chris
>>
>>   
>>> -gene
>>>




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