Replica/applylog creates new dirs with only DMDIR set, then sets mode with a separate wstat.
9vx/devfs-posix.c adds implicit 0400 to mkdir call to sustain till the wstat.
This patch makes u9fs to do the same.

A fix for replica/applylog to work over unmodified u9fs would be trivial, too.

Reference: /n/sources/patch/applied/u9fs-replica-mkdir
Date: Thu Mar 24 16:54:31 CET 2011
Signed-off-by: yarikos@gmail.com

--- /sys/src/cmd/unix/u9fs/u9fs.c	Thu Mar 24 16:48:27 2011
+++ /sys/src/cmd/unix/u9fs/u9fs.c	Thu Mar 24 16:48:23 2011
@@ -1605,7 +1605,7 @@
 			return -1;
 		}
 		/* race */
-		if(mkdir(npath, perm&0777) < 0){
+		if(mkdir(npath, (0400|perm)&0777) < 0){
 			*ep = strerror(errno);
 			free(npath);
 			return -1;