Re: [PATCH 1/6] nfsd: add a new EXPORT_OP_NOWCC flag to struct export_operations

[bfields@fieldses.org (J. Bruce Fields)]

This is great, thanks:

On Mon, Nov 30, 2020 at 04:24:50PM -0500, trondmy@kernel.org wrote:
> From: Jeff Layton <jeff.layton@primarydata.com>
> 
> With NFSv3 nfsd will always attempt to send along WCC data to the
> client. This generally involves saving off the in-core inode information
> prior to doing the operation on the given filehandle, and then issuing a
> vfs_getattr to it after the op.
> 
> Some filesystems (particularly clustered or networked ones) have an
> expensive ->getattr inode operation. Atomicitiy is also often difficult
> or impossible to guarantee on such filesystems. For those, we're best
> off not trying to provide WCC information to the client at all, and to
> simply allow it to poll for that information as needed with a GETATTR
> RPC.
> 
> This patch adds a new flags field to struct export_operations, and
> defines a new EXPORT_OP_NOWCC flag that filesystems can use to indicate
> that nfsd should not attempt to provide WCC info in NFSv3 replies. It
> also adds a blurb about the new flags field and flag to the exporting
> documentation.

In the v4 case I think it should also turn off the "atomic" flag in the
change_info4 structure that's returned by some operations.

(Out of curiosity: have you seen this cause actual bugs?)

--b.