knfsd: query filesystem for NFSv4 getattr of FATTR4_MAXNAME

Without this we always return 2^32-1 as the the maximum namelength.

Thanks to Andreas Gruenbacher for bug report and testing.
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Cc: Andreas Gruenbacher <agruen@suse.de>

fs/nfsd/nfs4xdr.c

@@ -1475,7 +1475,8 @@ nfsd4_encode_fattr(struct svc_fh *fhp, struct svc_export *exp,
 	err = vfs_getattr(exp->ex_mnt, dentry, &stat);
 	if (err)
 		goto out_nfserr;
-	if ((bmval0 & (FATTR4_WORD0_FILES_FREE | FATTR4_WORD0_FILES_TOTAL)) ||
+	if ((bmval0 & (FATTR4_WORD0_FILES_FREE | FATTR4_WORD0_FILES_TOTAL |
+			FATTR4_WORD0_MAXNAME)) ||
 	    (bmval1 & (FATTR4_WORD1_SPACE_AVAIL | FATTR4_WORD1_SPACE_FREE |
 		       FATTR4_WORD1_SPACE_TOTAL))) {
 		err = vfs_statfs(dentry, &statfs);
@@ -1721,7 +1722,7 @@ nfsd4_encode_fattr(struct svc_fh *fhp, struct svc_export *exp,
 	if (bmval0 & FATTR4_WORD0_MAXNAME) {
 		if ((buflen -= 4) < 0)
 			goto out_resource;
-		WRITE32(~(u32) 0);
+		WRITE32(statfs.f_namelen);
 	}
 	if (bmval0 & FATTR4_WORD0_MAXREAD) {
 		if ((buflen -= 8) < 0)