On 6/20/23 10:10 AM, Chuck Lever III wrote:
On Jun 20, 2023, at 11:27 AM, dai.ngo@xxxxxxxxxx wrote:
On 6/19/23 12:19 PM, Trond Myklebust wrote:
Hi Dai,
On Mon, 2023-06-19 at 10:02 -0700, dai.ngo@xxxxxxxxxx wrote:
Hi Trond,
I'm testing the NFS server with write delegation support and the
Linux client
using NFSv4.0 and run into a situation that needs your advise.
In this scenario, the NFS server grants the write delegation to the
client.
Later when the client returns delegation it sends the compound PUTFH,
GETATTR
and DELERETURN.
When the NFS server services the GETATTR, it detects that there is a
write
delegation on this file but it can not detect that this GETATTR
request was
sent from the same client that owns the write delegation (due to the
nature
of NFSv4.0 compound). As the result, the server sends CB_RECALL to
recall
the delegation and replies NFS4ERR_DELAY to the GETATTR request.
When the client receives the NFS4ERR_DELAY it retries with the same
compound
PUTFH, GETATTR, DELERETURN and server again replies the
NFS4ERR_DELAY. This
process repeats until the recall times out and the delegation is
revoked by
the server.
I noticed that the current order of GETATTR and DELEGRETURN was done
by
commit e144cbcc251f. Then later on, commit 8ac2b42238f5 was added to
drop
the GETATTR if the request was rejected with EACCES.
Do you have any advise on where, on server or client, this issue
should
be addressed?
This wants to be addressed in the server. The client has a very good
reason for wanting to retrieve the attributes before returning the
delegation here: it needs to update the change attribute while it is
still holding the delegation in order to ensure close-to-open cache
consistency.
Since you do have a stateid in the DELEGRETURN, it should be possible
to determine that this is indeed the client that holds the delegation.
Thank you Trond. I'll wait for Chuck to decide what to do next.
I don't have a technical objection to Trond's proposal. But until
the WG documents the interoperability requirements, I don't believe
it's something NFSD can sensibly support.
So, until the WG weighs in, NFSD won't offer write delegations to
NFSv4.0 clients. Let's be sure to document why in code comments.
Thank you Chuck, will do.
-Dai
--
Chuck Lever
