devtmpfs: replace ->mount with ->get_tree in public instance

To finalize mount API conversion, remove the ->mount op from the public
instance in favor of ->get_tree etc. Copy most ops from the underlying
ops vector (whether it's shmem or ramfs) and substitute our own
->get_tree which simply takes an extra reference on the existing internal
mount as before.

Thanks to Al for the fs_context_for_reconfigure() idea.

Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Link: https://lore.kernel.org/r/20250205213931.74614-4-sandeen@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index b848764ef0187fa5e04b35a3063800b7127cb14c..03a7c7902fcd2999e898825e32a2663b8616e937 100644 (file)
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -63,22 +63,6 @@ __setup("devtmpfs.mount=", mount_param);
 
 static struct vfsmount *mnt;
 
-static struct dentry *public_dev_mount(struct file_system_type *fs_type, int flags,
-                     const char *dev_name, void *data)
-{
-       struct super_block *s = mnt->mnt_sb;
-       int err;
-
-       atomic_inc(&s->s_active);
-       down_write(&s->s_umount);
-       err = reconfigure_single(s, flags, data);
-       if (err < 0) {
-               deactivate_locked_super(s);
-               return ERR_PTR(err);
-       }
-       return dget(s->s_root);
-}
-
 static struct file_system_type internal_fs_type = {
        .name = "devtmpfs",
 #ifdef CONFIG_TMPFS
@@ -89,9 +73,40 @@ static struct file_system_type internal_fs_type = {
        .kill_sb = kill_litter_super,
 };
 
+/* Simply take a ref on the existing mount */
+static int devtmpfs_get_tree(struct fs_context *fc)
+{
+       struct super_block *sb = mnt->mnt_sb;
+
+       atomic_inc(&sb->s_active);
+       down_write(&sb->s_umount);
+       fc->root = dget(sb->s_root);
+       return 0;
+}
+
+/* Ops are filled in during init depending on underlying shmem or ramfs type */
+struct fs_context_operations devtmpfs_context_ops = {};
+
+/* Call the underlying initialization and set to our ops */
+static int devtmpfs_init_fs_context(struct fs_context *fc)
+{
+       int ret;
+#ifdef CONFIG_TMPFS
+       ret = shmem_init_fs_context(fc);
+#else
+       ret = ramfs_init_fs_context(fc);
+#endif
+       if (ret < 0)
+               return ret;
+
+       fc->ops = &devtmpfs_context_ops;
+
+       return 0;
+}
+
 static struct file_system_type dev_fs_type = {
        .name = "devtmpfs",
-       .mount = public_dev_mount,
+       .init_fs_context = devtmpfs_init_fs_context,
 };
 
 static int devtmpfs_submit_req(struct req *req, const char *tmp)
@@ -442,6 +457,31 @@ static int __ref devtmpfsd(void *p)
        return 0;
 }
 
+/*
+ * Get the underlying (shmem/ramfs) context ops to build ours
+ */
+static int devtmpfs_configure_context(void)
+{
+       struct fs_context *fc;
+
+       fc = fs_context_for_reconfigure(mnt->mnt_root, mnt->mnt_sb->s_flags,
+                                       MS_RMT_MASK);
+       if (IS_ERR(fc))
+               return PTR_ERR(fc);
+
+       /* Set up devtmpfs_context_ops based on underlying type */
+       devtmpfs_context_ops.free             = fc->ops->free;
+       devtmpfs_context_ops.dup              = fc->ops->dup;
+       devtmpfs_context_ops.parse_param      = fc->ops->parse_param;
+       devtmpfs_context_ops.parse_monolithic = fc->ops->parse_monolithic;
+       devtmpfs_context_ops.get_tree         = &devtmpfs_get_tree;
+       devtmpfs_context_ops.reconfigure      = fc->ops->reconfigure;
+
+       put_fs_context(fc);
+
+       return 0;
+}
+
 /*
  * Create devtmpfs instance, driver-core devices will add their device
  * nodes here.
@@ -456,6 +496,13 @@ int __init devtmpfs_init(void)
                pr_err("unable to create devtmpfs %ld\n", PTR_ERR(mnt));
                return PTR_ERR(mnt);
        }
+
+       err = devtmpfs_configure_context();
+       if (err) {
+               pr_err("unable to configure devtmpfs type %d\n", err);
+               return err;
+       }
+
        err = register_filesystem(&dev_fs_type);
        if (err) {
                pr_err("unable to register devtmpfs type %d\n", err);