[Gluster-devel] Upcall details for NLINK

Soumya Koduri skoduri at redhat.com
Tue Sep 20 02:25:49 UTC 2016

On 09/19/2016 10:08 AM, Niels de Vos wrote:
> Duh, and now with the attachment. I'm going to get some coffee now.
> On Mon, Sep 19, 2016 at 06:22:58AM +0200, Niels de Vos wrote:
>> Hey Soumya,
>> do we have a description of the different actions that we expect/advise
>> users of upcall to take? I'm looking at the flags that are listed in
>> libglusterfs/src/upcall-utils.h and api/src/glfs-handles.h and passed in
>> the glfs_callback_inode_arg structure from api/src/glfs-handles.h.

Not very detailed. But a minimal description of each of these flags is 
provided in the definitions of these flags (now moved to the 

>> We have a NLINK flag, but that does not seem to carry the stat/iatt
>> attributes for the changed inode. It seems we send an upcall on file
>> removal that incudes NLINK, and just after that we send an other one
>> with FORGET.

 From the code, I see that it does seem to be sending stat of the inode 
being (un)linked. May be if it is the last link to be removed, stat 
structure could have been NULL. Could you please check with files with 
link count >1?

FORGET was not exactly related to removal/unlink of the file. It is to 
be sent whenever (protocol/)server does inode_forget which could be for 
various other reasons. But yeah, as you have said, when the last link is 
removed, since a FORGET gets definitely sent which invalidates the inode 
cache entry, there is no point sending NLINK flag just before that. We 
could have a check to avoid NLINK upcall if it is the last link of the 
file being removed.


>> This attachment in Bugzilla shows the behaviour:
>>   https://bugzilla.redhat.com/attachment.cgi?id=1202190
>> You'll need https://code.wireshark.org/review/17776 to decode the flags,
>> so I'll attach the tshark output to this email for your convenience.
>>   $ tshark -r /tmp/upcall_xid.1474190284.pcap.gz -V 'glusterfs.cbk'
>> Question: For the NLINK flag, should we not include the stat/iatt of the
>> modified inode? And only if the iatt->nlink is 0, a FORGET should get
>> sent? NLINK would then only happen when a (not the last) hardlink is
>> removed.
>> Thanks,
>> Niels
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