1 files changed, 287 insertions, 0 deletions
diff --git a/fs/filesystems.c b/fs/filesystems.c
new file mode 100644
index 000000000..90b8d879f
--- /dev/null
+++ b/fs/filesystems.c
@@ -0,0 +1,287 @@
+// 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>
+#include <linux/fs_parser.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;
+
+	if (fs->parameters &&
+	    !fs_validate_description(fs->name, fs->parameters))
+		return -EINVAL;
+
+	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);
+		if (!fs)
+			pr_warn_once("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);