Merge patch series "fs: last of the pseudofs mount api conversions"

Eric Sandeen <sandeen@redhat.com> says:

pstore used mount_single, which used to transparently do a
remount operation on a fresh mount of an existing superblock.
The new get_tree_single does not do this, but prior discussion
on fsdevel seems to indicate that this isn't expected to be a
problem. We can watch for issues.

devpts is just a forward port from work dhowells did already, and it
seems straightforward. I left error messages as they are rather than
converting to the mount API message channel for now.

devtmpfs was already converted, but left a .mount in place, rather
than using .get_tree. The solution to this is ... unique so some
scrutiny is probably wise.

The last patch removes reconfigure_single, mount_single, and
compare_single because no users remain, but we could also wait until
all conversions are done, and remove all infrastructure at that time
instead, if desired.

* patches from https://lore.kernel.org/r/20250205213931.74614-1-sandeen@redhat.com:
  vfs: remove some unused old mount api code
  devtmpfs: replace ->mount with ->get_tree in public instance
  vfs: Convert devpts to use the new mount API
  pstore: convert to the new mount API

Link: https://lore.kernel.org/r/20250205213931.74614-1-sandeen@redhat.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: brauner

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);