kern/122961: write operation on msdosfs file system causes panic

[Dominic Fandrey]

Bruce Evans wrote:
> On Tue, 22 Apr 2008, Dominic Fandrey wrote:
> 
>> Bruce Evans wrote:
>>> On Mon, 21 Apr 2008, Dominic Fandrey wrote:
>>> This seems to be a bug in usb (umass) or the particular usb drive...
>>> ...
>>>
>>> To check that this is the bug, mount msdosfs with -o 
>>> noclusterr,noclusterw
>>> under RELENG_7 or later (the bug also affects RELENG_6, but these mount
>>> options are broken in RELENG_6). ...
>>
>> # mount -t msdosfs -o 
>> noatime,noexec,-L=en_GB.UTF-8,noclusterr,noclusterw /dev/da0 /mnt/tmp
>> mount_msdosfs: /dev/da0: mount option <noclusterw> is unknown: Invalid 
>> argument
>>
>> It seems they are also broken under RELENG_7 from the day before 
>> yesterday.
> 
> Oops, it is indeed broken there too.  msdosfs in RELENG_7 is in the state
> that I thought RELENG_6 was in (missing critical MFCs only for nocluster*
> in the options list and to fix panics related to the dirty flag), while
> msdosfs in RELENG_6 is just too old to support clustering.
> 
> The broken nocluster* can be worked around by upgrading to a version of
> mount_msdsosfs(8) that hasn't been broken by using nmount(2).
> mount_msdsosfs(8) from RELENG_5 should work.

I feel reluctant about downgrading to 5.x mount_msdosfs, however I can confirm 
that cp with large files does _not_ cause a panic. As far as I understand this 
confirms your theory.

How can I provide more useful information?