[PATCH 2/5] samples/kernfs: Make filesystem mountable

[David Reaver <me@davidreaver.com>]

Implements the bare minimum functionality to safely mount and unmount the
sample_kernfs filesystem.

Signed-off-by: David Reaver <me@davidreaver.com>
---
 samples/kernfs/sample_kernfs.c | 69 +++++++++++++++++++++++++++++++++-
 1 file changed, 68 insertions(+), 1 deletion(-)

diff --git a/samples/kernfs/sample_kernfs.c b/samples/kernfs/sample_kernfs.c
index 82d4b73a4534..3ea8411a72ae 100644
--- a/samples/kernfs/sample_kernfs.c
+++ b/samples/kernfs/sample_kernfs.c
@@ -6,12 +6,79 @@

 #define pr_fmt(fmt) "%s: " fmt, __func__

+#include <linux/fs.h>
+#include <linux/fs_context.h>
+#include <linux/kernfs.h>
 #include <linux/kernel.h>
 #include <linux/module.h>

+#define SAMPLE_KERNFS_MAGIC 0x8d000ff0
+
+static void sample_kernfs_fs_context_free(struct fs_context *fc)
+{
+	struct kernfs_fs_context *kfc = fc->fs_private;
+
+	kernfs_free_fs_context(fc);
+	kfree(kfc);
+}
+
+static const struct fs_context_operations sample_kernfs_fs_context_ops = {
+	.get_tree	= kernfs_get_tree,
+	.free		= sample_kernfs_fs_context_free,
+};
+
+static int sample_kernfs_init_fs_context(struct fs_context *fc)
+{
+	struct kernfs_fs_context *kfc;
+	struct kernfs_root *root;
+	int err;
+
+	kfc = kzalloc(sizeof(struct kernfs_fs_context), GFP_KERNEL);
+	if (!kfc)
+		return -ENOMEM;
+
+	root = kernfs_create_root(NULL, 0, NULL);
+	if (IS_ERR(root)) {
+		err = PTR_ERR(root);
+		goto err_free_kfc;
+	}
+
+	kfc->root = root;
+	kfc->magic = SAMPLE_KERNFS_MAGIC;
+	fc->fs_private = kfc;
+	fc->ops = &sample_kernfs_fs_context_ops;
+	fc->global = true;
+
+	return 0;
+
+err_free_kfc:
+	kfree(kfc);
+	return err;
+}
+
+static void sample_kernfs_kill_sb(struct super_block *sb)
+{
+	struct kernfs_root *root = kernfs_root_from_sb(sb);
+
+	kernfs_kill_sb(sb);
+	kernfs_destroy_root(root);
+}
+
+static struct file_system_type sample_kernfs_fs_type = {
+	.name			= "sample_kernfs",
+	.init_fs_context	= sample_kernfs_init_fs_context,
+	.kill_sb		= sample_kernfs_kill_sb,
+	.fs_flags		= FS_USERNS_MOUNT,
+};
+
 static int __init sample_kernfs_init(void)
 {
-	pr_info("Loaded sample_kernfs module.\n");
+	int err;
+
+	err = register_filesystem(&sample_kernfs_fs_type);
+	if (err)
+		return err;
+
 	return 0;
 }