fs_context flavour for submounts

This is an eventual replacement for vfs_submount() uses.  Unlike the
"mount" and "remount" cases, the users of that thing are not in VFS -
they are buried in various ->d_automount() instances and rather than
converting them all at once we introduce the (thankfully small and
simple) infrastructure here and deal with the prospective users in
afs, nfs, etc. parts of the series.

Here we just introduce a new constructor (fs_context_for_submount())
along with the corresponding enum constant to be put into fc->purpose
for those.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/fs_context.c b/fs/fs_context.c
index 5e2c3aba1dd8..2bd652b6e848 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -69,6 +69,9 @@ static struct fs_context *alloc_fs_context(struct file_system_type *fs_type,
 	case FS_CONTEXT_FOR_MOUNT:
 		fc->user_ns = get_user_ns(fc->cred->user_ns);
 		break;
+	case FS_CONTEXT_FOR_SUBMOUNT:
+		fc->user_ns = get_user_ns(reference->d_sb->s_user_ns);
+		break;
 	case FS_CONTEXT_FOR_RECONFIGURE:
 		/* We don't pin any namespaces as the superblock's
 		 * subscriptions cannot be changed at this point.
@@ -106,6 +109,13 @@ struct fs_context *fs_context_for_reconfigure(struct dentry *dentry,
 }
 EXPORT_SYMBOL(fs_context_for_reconfigure);
 
+struct fs_context *fs_context_for_submount(struct file_system_type *type,
+					   struct dentry *reference)
+{
+	return alloc_fs_context(type, reference, 0, 0, FS_CONTEXT_FOR_SUBMOUNT);
+}
+EXPORT_SYMBOL(fs_context_for_submount);
+
 void fc_drop_locked(struct fs_context *fc)
 {
 	struct super_block *sb = fc->root->d_sb;