[Pvfs2-developers] read buffer bug

[Sam Lang]

Its in CVS now.  Thanks Murali for the fix, and Phil for the report.

-sam

On Nov 30, 2006, at 10:15 AM, Phil Carns wrote:

> Thanks for the quick fix!
>
> Murali Vilayannur wrote:
>> Hi guys,
>> I am really sorry about this. I am surprised we did not catch this
>> earlier. This was basically introduced by the file.c/bufmap.c  
>> cleanups
>> that I had done a while back.
>> Attached patch should fix this error.
>> thanks for the testcase, Phil!
>> Murali
>> On 11/29/06, Phil Carns <pcarns at wastedcycles.org> wrote:
>>> I ran into a problem today with the 2.6.0 release.  This happened to
>>> show up in the read04 LTP test, but not reliably.  I have attached a
>>> test program that I think does trigger it reliably, though.
>>>
>>> When run on ext3:
>>>
>>>         /home/pcarns> ./testme /tmp/foo.txt
>>>         read returned: 7, test_buf: hello   world
>>>
>>> When run on pvfs2:
>>>
>>>         /home/pcarns> ./testme /mnt/pvfs2/foo.txt
>>>         read returned: 7, test_buf: hello
>>>
>>> (or sometimes you might get garbage after the "hello")
>>>
>>> The test program creates a string buffer with "goodbye world"  
>>> stored in
>>> it.  It then reads the string "hello  " out of a file into the  
>>> beginning
>>> of that buffer.   The result should be that the final resulting  
>>> string
>>> is "hello  world".
>>>
>>> The trick that makes this fail is asking to read more than 7  
>>> bytes from
>>> the file.
>>>
>>> In this particular test program, we attempt to do a read of 255  
>>> bytes.
>>> There are only 7 bytes in the file, though.  The return code from  
>>> read
>>> accurately reflects this.  However, rather than just fill in the  
>>> first 7
>>> bytes of the buffer, it looks like PVFS2 is overwriting the full 255
>>> bytes.  What ends up in those trailing 248 bytes is somewhat random.
>>>
>>> I suspect that somewhere in the kernel module there is a  
>>> copy_to_user()
>>> call that is copying the number of bytes requested by the read  
>>> rather
>>> than the number of bytes returned by the servers.
>>>
>>> -Phil
>>>
>>>
>>> _______________________________________________
>>> Pvfs2-developers mailing list
>>> Pvfs2-developers at beowulf-underground.org
>>> http://www.beowulf-underground.org/mailman/listinfo/pvfs2-developers
>>>
>>>
>>>
>>>
>
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