/* *  linux/fs/filesystems.c * *  Copyright (C) 1991, 1992  Linus Torvalds * *  table of configured filesystems */ #include <linux/syscalls.h>#include <linux/fs.h>#include <linux/slab.h>#include <linux/kmod.h>#include <linux/init.h>#include <linux/module.h>#include <linux/sched.h>	/* for 'current' */#include <asm/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 */void get_filesystem(struct file_system_type *fs){	__module_get(fs->owner);} void put_filesystem(struct file_system_type *fs){	module_put(fs->owner);} static struct file_system_type **find_filesystem(const char *name){	struct file_system_type **p;	for (p=&file_systems; *p; p=&(*p)->next)		if (strcmp((*p)->name,name) == 0)			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)		return -EINVAL;	if (fs->next)		return -EBUSY;	INIT_LIST_HEAD(&fs->fs_supers);	write_lock(&file_systems_lock);	p = find_filesystem(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);			return 0;		}		tmp = &(*tmp)->next;	}	write_unlock(&file_systems_lock);	return -EINVAL;} EXPORT_SYMBOL(unregister_filesystem); static int fs_index(const char __user * __name){	struct file_system_type * tmp;	char * 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) == 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.  */asmlinkage long sys_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;} int 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;} struct file_system_type *get_fs_type(const char *name){	struct file_system_type *fs; 	read_lock(&file_systems_lock);	fs = *(find_filesystem(name));	if (fs && !try_module_get(fs->owner))		fs = NULL;	read_unlock(&file_systems_lock);	if (!fs && (request_module("%s", name) == 0)) {		read_lock(&file_systems_lock);		fs = *(find_filesystem(name));		if (fs && !try_module_get(fs->owner))			fs = NULL;		read_unlock(&file_systems_lock);	}	return fs;} EXPORT_SYMBOL(get_fs_type);