v4.19.13 snapshot.
diff --git a/fs/filesystems.c b/fs/filesystems.c
new file mode 100644
index 0000000..b03f57b
--- /dev/null
+++ b/fs/filesystems.c
@@ -0,0 +1,280 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/filesystems.c
+ *
+ * Copyright (C) 1991, 1992 Linus Torvalds
+ *
+ * table of configured filesystems
+ */
+
+#include <linux/syscalls.h>
+#include <linux/fs.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <linux/kmod.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+
+/*
+ * Handling of filesystem drivers list.
+ * Rules:
+ * Inclusion to/removals from/scanning of list are protected by spinlock.
+ * During the unload module must call unregister_filesystem().
+ * We can access the fields of list element if:
+ * 1) spinlock is held or
+ * 2) we hold the reference to the module.
+ * The latter can be guaranteed by call of try_module_get(); if it
+ * returned 0 we must skip the element, otherwise we got the reference.
+ * Once the reference is obtained we can drop the spinlock.
+ */
+
+static struct file_system_type *file_systems;
+static DEFINE_RWLOCK(file_systems_lock);
+
+/* WARNING: This can be used only if we _already_ own a reference */
+struct file_system_type *get_filesystem(struct file_system_type *fs)
+{
+ __module_get(fs->owner);
+ return fs;
+}
+
+void put_filesystem(struct file_system_type *fs)
+{
+ module_put(fs->owner);
+}
+
+static struct file_system_type **find_filesystem(const char *name, unsigned len)
+{
+ struct file_system_type **p;
+ for (p = &file_systems; *p; p = &(*p)->next)
+ if (strncmp((*p)->name, name, len) == 0 &&
+ !(*p)->name[len])
+ break;
+ return p;
+}
+
+/**
+ * register_filesystem - register a new filesystem
+ * @fs: the file system structure
+ *
+ * Adds the file system passed to the list of file systems the kernel
+ * is aware of for mount and other syscalls. Returns 0 on success,
+ * or a negative errno code on an error.
+ *
+ * The &struct file_system_type that is passed is linked into the kernel
+ * structures and must not be freed until the file system has been
+ * unregistered.
+ */
+
+int register_filesystem(struct file_system_type * fs)
+{
+ int res = 0;
+ struct file_system_type ** p;
+
+ BUG_ON(strchr(fs->name, '.'));
+ if (fs->next)
+ return -EBUSY;
+ write_lock(&file_systems_lock);
+ p = find_filesystem(fs->name, strlen(fs->name));
+ if (*p)
+ res = -EBUSY;
+ else
+ *p = fs;
+ write_unlock(&file_systems_lock);
+ return res;
+}
+
+EXPORT_SYMBOL(register_filesystem);
+
+/**
+ * unregister_filesystem - unregister a file system
+ * @fs: filesystem to unregister
+ *
+ * Remove a file system that was previously successfully registered
+ * with the kernel. An error is returned if the file system is not found.
+ * Zero is returned on a success.
+ *
+ * Once this function has returned the &struct file_system_type structure
+ * may be freed or reused.
+ */
+
+int unregister_filesystem(struct file_system_type * fs)
+{
+ struct file_system_type ** tmp;
+
+ write_lock(&file_systems_lock);
+ tmp = &file_systems;
+ while (*tmp) {
+ if (fs == *tmp) {
+ *tmp = fs->next;
+ fs->next = NULL;
+ write_unlock(&file_systems_lock);
+ synchronize_rcu();
+ return 0;
+ }
+ tmp = &(*tmp)->next;
+ }
+ write_unlock(&file_systems_lock);
+
+ return -EINVAL;
+}
+
+EXPORT_SYMBOL(unregister_filesystem);
+
+#ifdef CONFIG_SYSFS_SYSCALL
+static int fs_index(const char __user * __name)
+{
+ struct file_system_type * tmp;
+ struct filename *name;
+ int err, index;
+
+ name = getname(__name);
+ err = PTR_ERR(name);
+ if (IS_ERR(name))
+ return err;
+
+ err = -EINVAL;
+ read_lock(&file_systems_lock);
+ for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
+ if (strcmp(tmp->name, name->name) == 0) {
+ err = index;
+ break;
+ }
+ }
+ read_unlock(&file_systems_lock);
+ putname(name);
+ return err;
+}
+
+static int fs_name(unsigned int index, char __user * buf)
+{
+ struct file_system_type * tmp;
+ int len, res;
+
+ read_lock(&file_systems_lock);
+ for (tmp = file_systems; tmp; tmp = tmp->next, index--)
+ if (index <= 0 && try_module_get(tmp->owner))
+ break;
+ read_unlock(&file_systems_lock);
+ if (!tmp)
+ return -EINVAL;
+
+ /* OK, we got the reference, so we can safely block */
+ len = strlen(tmp->name) + 1;
+ res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
+ put_filesystem(tmp);
+ return res;
+}
+
+static int fs_maxindex(void)
+{
+ struct file_system_type * tmp;
+ int index;
+
+ read_lock(&file_systems_lock);
+ for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
+ ;
+ read_unlock(&file_systems_lock);
+ return index;
+}
+
+/*
+ * Whee.. Weird sysv syscall.
+ */
+SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
+{
+ int retval = -EINVAL;
+
+ switch (option) {
+ case 1:
+ retval = fs_index((const char __user *) arg1);
+ break;
+
+ case 2:
+ retval = fs_name(arg1, (char __user *) arg2);
+ break;
+
+ case 3:
+ retval = fs_maxindex();
+ break;
+ }
+ return retval;
+}
+#endif
+
+int __init get_filesystem_list(char *buf)
+{
+ int len = 0;
+ struct file_system_type * tmp;
+
+ read_lock(&file_systems_lock);
+ tmp = file_systems;
+ while (tmp && len < PAGE_SIZE - 80) {
+ len += sprintf(buf+len, "%s\t%s\n",
+ (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
+ tmp->name);
+ tmp = tmp->next;
+ }
+ read_unlock(&file_systems_lock);
+ return len;
+}
+
+#ifdef CONFIG_PROC_FS
+static int filesystems_proc_show(struct seq_file *m, void *v)
+{
+ struct file_system_type * tmp;
+
+ read_lock(&file_systems_lock);
+ tmp = file_systems;
+ while (tmp) {
+ seq_printf(m, "%s\t%s\n",
+ (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
+ tmp->name);
+ tmp = tmp->next;
+ }
+ read_unlock(&file_systems_lock);
+ return 0;
+}
+
+static int __init proc_filesystems_init(void)
+{
+ proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
+ return 0;
+}
+module_init(proc_filesystems_init);
+#endif
+
+static struct file_system_type *__get_fs_type(const char *name, int len)
+{
+ struct file_system_type *fs;
+
+ read_lock(&file_systems_lock);
+ fs = *(find_filesystem(name, len));
+ if (fs && !try_module_get(fs->owner))
+ fs = NULL;
+ read_unlock(&file_systems_lock);
+ return fs;
+}
+
+struct file_system_type *get_fs_type(const char *name)
+{
+ struct file_system_type *fs;
+ const char *dot = strchr(name, '.');
+ int len = dot ? dot - name : strlen(name);
+
+ fs = __get_fs_type(name, len);
+ if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
+ fs = __get_fs_type(name, len);
+ WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
+ }
+
+ if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
+ put_filesystem(fs);
+ fs = NULL;
+ }
+ return fs;
+}
+
+EXPORT_SYMBOL(get_fs_type);