From 0e885e846d96df0c8a4a829b1ad355a82ccda656 Mon Sep 17 00:00:00 2001
From: Frank van der Linden <fllinden@amazon.com>
Date: Tue, 23 Jun 2020 22:39:27 +0000
Subject: [PATCH] nfsd: add fattr support for user extended attributes

Check if user extended attributes are supported for an inode,
and return the answer when being queried for file attributes.

An exported filesystem can now signal its RFC8276 user extended
attributes capability.

Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs4xdr.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 8bacc0ceae19..259d5ad0e3f4 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -3213,6 +3213,15 @@ out_acl:
 	}
 #endif
 
+	if (bmval2 & FATTR4_WORD2_XATTR_SUPPORT) {
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
+			goto out_resource;
+		err = xattr_supported_namespace(d_inode(dentry),
+						XATTR_USER_PREFIX);
+		*p++ = cpu_to_be32(err == 0);
+	}
+
 	attrlen = htonl(xdr->buf->len - attrlen_offset - 4);
 	write_bytes_to_xdr_buf(xdr->buf, attrlen_offset, &attrlen, 4);
 	status = nfs_ok;