erofs: decouple struct erofs_anon_fs_type

  - Move the `struct erofs_anon_fs_type` to super.c and expose it
    in preparation for the upcoming page cache share feature;

  - Remove the `.owner` field, as they are all internal mounts and
    fully managed by EROFS.  Retaining `.owner` would unnecessarily
    increment module reference counts, preventing the EROFS kernel
    module from being unloaded.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

Author: hsiangkao

fs/erofs/fscache.c

@@ -3,7 +3,6 @@
  * Copyright (C) 2022, Alibaba Cloud
  * Copyright (C) 2022, Bytedance Inc. All rights reserved.
  */
-#include <linux/pseudo_fs.h>
 #include <linux/fscache.h>
 #include "internal.h"
 
@@ -13,18 +12,6 @@ static LIST_HEAD(erofs_domain_list);
 static LIST_HEAD(erofs_domain_cookies_list);
 static struct vfsmount *erofs_pseudo_mnt;
 
-static int erofs_anon_init_fs_context(struct fs_context *fc)
-{
-	return init_pseudo(fc, EROFS_SUPER_MAGIC) ? 0 : -ENOMEM;
-}
-
-static struct file_system_type erofs_anon_fs_type = {
-	.owner		= THIS_MODULE,
-	.name           = "pseudo_erofs",
-	.init_fs_context = erofs_anon_init_fs_context,
-	.kill_sb        = kill_anon_super,
-};
-
 struct erofs_fscache_io {
 	struct netfs_cache_resources cres;
 	struct iov_iter		iter;

fs/erofs/internal.h

@@ -185,6 +185,8 @@ static inline bool erofs_is_fileio_mode(struct erofs_sb_info *sbi)
 	return IS_ENABLED(CONFIG_EROFS_FS_BACKED_BY_FILE) && sbi->dif0.file;
 }
 
+extern struct file_system_type erofs_anon_fs_type;
+
 static inline bool erofs_is_fscache_mode(struct super_block *sb)
 {
 	return IS_ENABLED(CONFIG_EROFS_FS_ONDEMAND) &&

fs/erofs/super.c

@@ -11,6 +11,7 @@
 #include <linux/fs_parser.h>
 #include <linux/exportfs.h>
 #include <linux/backing-dev.h>
+#include <linux/pseudo_fs.h>
 #include "xattr.h"
 
 #define CREATE_TRACE_POINTS
@@ -945,6 +946,19 @@ static struct file_system_type erofs_fs_type = {
 };
 MODULE_ALIAS_FS("erofs");
 
+#if defined(CONFIG_EROFS_FS_ONDEMAND)
+static int erofs_anon_init_fs_context(struct fs_context *fc)
+{
+	return init_pseudo(fc, EROFS_SUPER_MAGIC) ? 0 : -ENOMEM;
+}
+
+struct file_system_type erofs_anon_fs_type = {
+	.name           = "pseudo_erofs",
+	.init_fs_context = erofs_anon_init_fs_context,
+	.kill_sb        = kill_anon_super,
+};
+#endif
+
 static int __init erofs_module_init(void)
 {
 	int err;