On Mon, Nov 30, 2020 at 05:58:42PM -0500, J. Bruce Fields wrote:
> This is great, thanks:
>
> On Mon, Nov 30, 2020 at 04:24:50PM -0500, trondmy@xxxxxxxxxx wrote:
> > From: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>
> >
> > 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.
And then it looks to me like all you need is something like the
following, no need for a fh_no_wcc field or anything, just skip the
stuff you don't want in fill_post_wcc when the flag is set:
--b.
diff --git a/fs/nfsd/nfs3xdr.c b/fs/nfsd/nfs3xdr.c
index bd4edf904bba..0b51f9dd0752 100644
--- a/fs/nfsd/nfs3xdr.c
+++ b/fs/nfsd/nfs3xdr.c
@@ -289,13 +289,16 @@ void fill_post_wcc(struct svc_fh *fhp)
{
bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
struct inode *inode = d_inode(fhp->fh_dentry);
+ struct export_operations *ops = inode->i_sb->s_export_op;
if (fhp->fh_post_saved)
printk("nfsd: inode locked twice during operation.\n");
fhp->fh_post_saved = true;
- if (!v4 || !inode->i_sb->s_export_op->fetch_iversion) {
+ if (ops->flags & EXPORT_OP_NOWCC)
+ fhp->fh_post_saved = false;
+ else if (!v4 || !ops->fetch_iversion) {
__be32 err = fh_getattr(fhp, &fhp->fh_post_attr);
if (err) {
fhp->fh_post_saved = false;
