teach vfs_get_tree() to handle subtype, switch do_new_mount() to it

Roll the handling of subtypes into do_new_mount() and vfs_get_tree().  The
former determines any subtype string and hangs it off the fs_context; the
latter applies it.

Make do_new_mount() create, parameterise and commit an fs_context and
create a mount for itself rather than calling vfs_kern_mount().

[AV -- missing kstrdup()]
[AV -- ... and no kstrdup() if we get to setting ->s_submount - we
simply transfer it from fc, leaving NULL behind]
[AV -- constify ->s_submount, while we are at it]

Reviewed-by: David Howells <dhowells@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/super.c b/fs/super.c
index fc3887277ad1..b91b6df05b67 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1262,6 +1262,11 @@ int vfs_get_tree(struct fs_context *fc)
         sb = fc->root->d_sb;
         WARN_ON(!sb->s_bdi);
 
+        if (fc->subtype && !sb->s_subtype) {
+                sb->s_subtype = fc->subtype;
+                fc->subtype = NULL;
+        }
+
         /*
          * Write barrier is for super_cache_count(). We place it before setting
          * SB_BORN as the data dependency between the two functions is the