NFSD: Don't give out read delegations on creates

When an exclusive create is done with the mode bits
set (aka open(testfile, O_CREAT | O_EXCL, 0777)) this
causes a OPEN op followed by a SETATTR op. When a
read delegation is given in the OPEN, it causes
the SETATTR to delay with EAGAIN until the
delegation is recalled.

This patch caused exclusive creates to give out
a write delegation (which turn into no delegation)
which allows the SETATTR seamlessly succeed.
Signed-off-by: Steve Dickson <steved@redhat.com>
[bfields: do this for any CREATE, not just exclusive; comment]
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4state.c

@@ -3113,8 +3113,17 @@ nfs4_open_delegation(struct net *net, struct svc_fh *fh,
 				goto out;
 			if (!cb_up || !(oo->oo_flags & NFS4_OO_CONFIRMED))
 				goto out;
+			/*
+			 * Also, if the file was opened for write or
+			 * create, there's a good chance the client's
+			 * about to write to it, resulting in an
+			 * immediate recall (since we don't support
+			 * write delegations):
+			 */
 			if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE)
 				flag = NFS4_OPEN_DELEGATE_WRITE;
+			else if (open->op_create == NFS4_OPEN_CREATE)
+				flag = NFS4_OPEN_DELEGATE_WRITE;
 			else
 				flag = NFS4_OPEN_DELEGATE_READ;
 			break;