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 <behlendorf1@llnl.gov>
Closes #473

diff --git a/cmd/zfs/zfs_main.c b/cmd/zfs/zfs_main.c
index a052be5..518000c 100644 (file)
--- 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);

diff --git a/lib/libspl/include/sys/mount.h b/lib/libspl/include/sys/mount.h
index d4ac6a9..145e785 100644 (file)
--- a/lib/libspl/include/sys/mount.h
+++ b/lib/libspl/include/sys/mount.h
@@ -73,4 +73,11 @@
 # define MS_DETACH     0x00000002
 #endif /* MNT_DETACH */
 
+/*
+ * Overlay mount is default in Linux, but for solaris/zfs
+ * compatibility, MS_OVERLAY is defined to explicitly have the user
+ * provide a flag (-O) to mount over a non empty directory.
+ */
+#define MS_OVERLAY      0x00000004
+
 #endif /* _LIBSPL_SYS_MOUNT_H */

diff --git a/lib/libzfs/libzfs_mount.c b/lib/libzfs/libzfs_mount.c
index 6758f6a..0fe83e5 100644 (file)
--- a/lib/libzfs/libzfs_mount.c
+++ b/lib/libzfs/libzfs_mount.c
@@ -440,9 +440,11 @@ zfs_mount(zfs_handle_t *zhp, const char *options, int flags)
 
        /*
         * Determine if the mountpoint is empty.  If so, refuse to perform the
-        * mount.  We don't perform this check if 'remount' is specified.
+        * mount.  We don't perform this check if 'remount' is
+        * specified or if overlay option(-O) is given
         */
-       if (!remount && !dir_is_empty(mountpoint)) {
+       if ((flags & MS_OVERLAY) == 0 && !remount &&
+           !dir_is_empty(mountpoint)) {
                zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
                    "directory is not empty"));
                return (zfs_error_fmt(hdl, EZFS_MOUNTFAILED,