[Pvfs2-developers] kernel readdir question

[Sam Lang]

On Nov 8, 2006, at 11:45 AM, Murali Vilayannur wrote:

> Hi Phil,
> I dont have the code to check up on that right now. but if I recall
> correctly, we don't want to fill . and .. multiple times and we use
> the directory_version check as a crude way to know when to fill it and
> when not.
> i.e. if that was 0, we are starting out to read the directory and so
> we fill . and ..
> After the entire readdir is over we set the version back to 0.
> It is possible there is a bug. I can check it up later today and get
> back to you.

 From what I can tell the directory_version gets set to the mtime  
after the first upcall.  If future upcalls changed the mtime, we used  
to start over, and we didn't want to call filldir again on . and ..

But we recently changed this code to not start over if the directory  
version changed from one readdir call to the next (it was causing  
duplicate entries, see:  http://www.beowulf-underground.org/pipermail/ 
pvfs2-developers/2006-October/002739.html), instead we just update  
the directory version stored in the inode.  There's also the diff of  
the Murali's changes:

http://www.pvfs.org/cgi-bin/pvfs2/viewcvs/viewcvs.cgi/pvfs2/src/ 
kernel/linux-2.6/dir.c.diff?r1=1.45&r2=1.46

The directory_version gets set back to 0 once we hit the end of a  
directory, so I could imagine that killing an ls while its listing a  
directory with many entries would cause the directory version to be  
set to the mtime of the last readdir call before the abort.  This  
would give the behavior of the . and .. not showing up in the next  
listing, but as long as that listing was allowed to complete, the  
directory_version would be set back to 0 again.

Given that we removed the code that restarts if the version changes  
on us midway through a listing, can we assume that the position will  
be set to 0 _only_ on the first readdir call?  This would allow us to  
remove the directory_version == 0 check.  In fact we should be able  
to remove the PVFS_READDIR_END check that sets the directory_version  
back to 0 as well...

-sam

> thanks,
> Murali
>
> On 11/8/06, Phil Carns <pcarns at wastedcycles.org> wrote:
>> It's been a while since I've seen this bug first hand, but I am  
>> just now
>> getting around to looking at it.
>>
>> Every once in a while we have seen cases where "ls -al" in a pvfs2
>> directory fails to show the "." and ".." entries.  I _think_ this has
>> mainly occurred after restarting pvfs2-client and/or pvfs2-server,  
>> but I
>> am not certain.  I can't seem to reproduce it.
>>
>> At any rate, looking at the code in dir.c, it seems like filling  
>> in the
>> "." and ".." entries should be pretty much automatic.  However,  
>> there is
>> an if statement wrapped around the filldir() calls that looks like  
>> this:
>>
>>          if (pvfs2_inode->directory_version == 0)
>>          {
>>
>> Anyone know what the purpose if this check is?  It seems to me  
>> like "."
>> and ".." should be entries for position 0 and 1 regardless of the
>> directory version, but I may be missing something.
>>
>> -Phil
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