NFSv4.2: Fix detection of "Proxying of Times" server support

According to draft-ietf-nfsv4-delstid-07:
   If a server informs the client via the fattr4_open_arguments
   attribute that it supports
   OPEN_ARGS_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS and it returns a valid
   delegation stateid for an OPEN operation which sets the
   OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS flag, then it MUST query the
   client via a CB_GETATTR for the fattr4_time_deleg_access (see
   Section 5.2) attribute and fattr4_time_deleg_modify attribute (see
   Section 5.2).

Thus, we should look that the server supports proxying of times via
OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS.

We want to be extra pedantic and continue to check that FATTR4_TIME_DELEG_ACCESS
and FATTR4_TIME_DELEG_MODIFY are set. The server needs to expose both for the
client to correctly detect "Proxying of Times" support.
Signed-off-by: Roi Azarzar <roi.azarzar@vastdata.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Fixes: dcb3c20f ("NFSv4: Add a capability for delegated attributes")
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

fs/nfs/nfs4proc.c

@@ -3904,6 +3904,18 @@ static void nfs4_close_context(struct nfs_open_context *ctx, int is_sync)
 #define FATTR4_WORD2_NFS41_MASK (2*FATTR4_WORD2_SUPPATTR_EXCLCREAT - 1UL)
 #define FATTR4_WORD2_NFS42_MASK (2*FATTR4_WORD2_OPEN_ARGUMENTS - 1UL)
 
+#define FATTR4_WORD2_NFS42_TIME_DELEG_MASK \
+	(FATTR4_WORD2_TIME_DELEG_MODIFY|FATTR4_WORD2_TIME_DELEG_ACCESS)
+static bool nfs4_server_delegtime_capable(struct nfs4_server_caps_res *res)
+{
+	u32 share_access_want = res->open_caps.oa_share_access_want[0];
+	u32 attr_bitmask = res->attr_bitmask[2];
+
+	return (share_access_want & NFS4_SHARE_WANT_DELEG_TIMESTAMPS) &&
+	       ((attr_bitmask & FATTR4_WORD2_NFS42_TIME_DELEG_MASK) ==
+					FATTR4_WORD2_NFS42_TIME_DELEG_MASK);
+}
+
 static int _nfs4_server_capabilities(struct nfs_server *server, struct nfs_fh *fhandle)
 {
 	u32 minorversion = server->nfs_client->cl_minorversion;
@@ -3982,8 +3994,6 @@ static int _nfs4_server_capabilities(struct nfs_server *server, struct nfs_fh *f
 #endif
 		if (res.attr_bitmask[0] & FATTR4_WORD0_FS_LOCATIONS)
 			server->caps |= NFS_CAP_FS_LOCATIONS;
-		if (res.attr_bitmask[2] & FATTR4_WORD2_TIME_DELEG_MODIFY)
-			server->caps |= NFS_CAP_DELEGTIME;
 		if (!(res.attr_bitmask[0] & FATTR4_WORD0_FILEID))
 			server->fattr_valid &= ~NFS_ATTR_FATTR_FILEID;
 		if (!(res.attr_bitmask[1] & FATTR4_WORD1_MODE))
@@ -4011,6 +4021,8 @@ static int _nfs4_server_capabilities(struct nfs_server *server, struct nfs_fh *f
 		if (res.open_caps.oa_share_access_want[0] &
 		    NFS4_SHARE_WANT_OPEN_XOR_DELEGATION)
 			server->caps |= NFS_CAP_OPEN_XOR;
+		if (nfs4_server_delegtime_capable(&res))
+			server->caps |= NFS_CAP_DELEGTIME;
 
 		memcpy(server->cache_consistency_bitmask, res.attr_bitmask, sizeof(server->cache_consistency_bitmask));
 		server->cache_consistency_bitmask[0] &= FATTR4_WORD0_CHANGE|FATTR4_WORD0_SIZE;