NFSv3 caching vs NFSv4

Hello everyone,

Performing some attribute caching tests I think I found some inconsistencies between nfsv3 and nfsv4. Running a kernel based on rhel6.3 (2.6.32-279.el6.x86_64) I found nfsv4 doesn't manage a file modified on the server side (even with the noac mount option) while nfsv3 does.

My test will be modifying a file every second on the server mount point:

[root@nfs ~]# FILE=/tmp/nfs_server/myfile ; while true ; do sleep 1 ; sed -i 's/text1/text2/g' $FILE ; cat $FILE ; sleep 1; sed -i 's/text2/text1/g' $FILE ; cat $FILE ; done text2
text1
text2
text1
text2
(and so on...)

Meanwhile, the client (which BTW is the same machine) will read the file every second :

With NFSv4:

[root@nfs ~]# mount -o noac,vers=4 nfs:/tmp/nfs_server/ /tmp/nfs_client/ [root@nfs ~]# for i in 1 2 3 4 5 ; do cat /tmp/nfs_client/myfile; sleep 1 ; done text2
text1
text1
text1
text1

With NFSv3:
[root@nfs ~]# mount -o noac,vers=3 nfs:/tmp/nfs_server/ /tmp/nfs_client/ [root@nfs ~]# for i in 1 2 3 4 5 ; do cat /tmp/nfs_client/myfile; sleep 1 ; done text1
text2
text1
text2
text1

I can see in the tcpdump traces how the new change attribute and the FATTR4_TIME_MODIFY attributes are well received but it's as if the nfs client were ignoring these changes. I've been searching in the NFS list but I didn't find anything similar. Is this a bug or just a normal behavior? Sorry if it has been already pointed out.

Regards,

Diego Moreno

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I believe sed -i is actually doing a rename not a file modification. So the problem is likely another symptom of the bug that delegations aren't revoked on rename/link/unlink. Hoping to post the latest draft of patches to fix that later today.

--b.

Ok, so this is a delegation bug. I think you're rigth Bruce, I cannot see the bug if I just modify the file with vi.

I'll try your delegation patch ASAP.

Thanks,

Diego