Add overlay(-O) mount option support

Linux supports mounting over non-empty directories by default.
In Solaris this is not the case and -O option is required for
zfs mount to mount a zfs filesystem over a non-empty directory.

For compatibility, I've added support for -O option to mount
zfs filesystems over non-empty directories if the user wants
to, just like in Solaris.

I've defined MS_OVERLAY to record it in the flags variable if
the -O option is supplied.  The flags variable passes through
a few functions and its checked before performing the empty
directory check in zfs_mount function.  If -O is given, the
check is not performed.

Signed-off-by: Brian Behlendorf <[email protected]>
Closes #473

1 files changed, 4 insertions, 2 deletions

diff --git a/cmd/zfs/zfs_main.c b/cmd/zfs/zfs_main.c
index a052be520..518000cf1 100644
--- a/cmd/zfs/zfs_main.c
+++ b/cmd/zfs/zfs_main.c
@@ -5469,7 +5469,7 @@ share_mount(int op, int argc, char **argv)
 	int flags = 0;
 
 	/* check options */
-	while ((c = getopt(argc, argv, op == OP_MOUNT ? ":avo:" : "a"))
+	while ((c = getopt(argc, argv, op == OP_MOUNT ? ":avo:O" : "a"))
 	    != -1) {
 		switch (c) {
 		case 'a':
@@ -5491,7 +5491,9 @@ share_mount(int op, int argc, char **argv)
 			/* option validation is done later */
 			append_options(options, optarg);
 			break;
-
+		case 'O':
+			flags |= MS_OVERLAY;
+			break;
 		case ':':
 			(void) fprintf(stderr, gettext("missing argument for "
 			    "'%c' option\n"), optopt);