[linux.git] / fs / filesystems.c

// 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->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);
		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);
Commit	Line	Data
b2441318	1	// SPDX-License-Identifier: GPL-2.0
1da177e4 LT	2	/*
	3	* linux/fs/filesystems.c
	4	*
	5	* Copyright (C) 1991, 1992 Linus Torvalds
	6	*
	7	* table of configured filesystems
	8	*/
	9
	10	#include <linux/syscalls.h>
	11	#include <linux/fs.h>
68274007 AD	12	#include <linux/proc_fs.h>
68274007 AD	13	#include <linux/seq_file.h>
1da177e4 LT	14	#include <linux/kmod.h>
	15	#include <linux/init.h>
	16	#include <linux/module.h>
5a0e3ad6	17	#include <linux/slab.h>
7c0f6ba6	18	#include <linux/uaccess.h>
3e1aeb00	19	#include <linux/fs_parser.h>
1da177e4 LT	20
	21	/*
	22	* Handling of filesystem drivers list.
	23	* Rules:
	24	* Inclusion to/removals from/scanning of list are protected by spinlock.
	25	* During the unload module must call unregister_filesystem().
	26	* We can access the fields of list element if:
	27	* 1) spinlock is held or
	28	* 2) we hold the reference to the module.
	29	* The latter can be guaranteed by call of try_module_get(); if it
	30	* returned 0 we must skip the element, otherwise we got the reference.
	31	* Once the reference is obtained we can drop the spinlock.
	32	*/
	33
	34	static struct file_system_type *file_systems;
	35	static DEFINE_RWLOCK(file_systems_lock);
	36
	37	/* WARNING: This can be used only if we _already_ own a reference */
ee416bcd	38	struct file_system_type get_filesystem(struct file_system_type fs)
1da177e4 LT	39	{
1da177e4 LT	40	__module_get(fs->owner);
ee416bcd	41	return fs;
1da177e4 LT	42	}
	43
	44	void put_filesystem(struct file_system_type *fs)
	45	{
	46	module_put(fs->owner);
	47	}
	48
79c0b2df	49	static struct file_system_type *find_filesystem(const char name, unsigned len)
1da177e4 LT	50	{
1da177e4 LT	51	struct file_system_type **p;
558041d8 AV	52	for (p = &file_systems; p; p = &(p)->next)
	53	if (strncmp((*p)->name, name, len) == 0 &&
	54	!(*p)->name[len])
1da177e4 LT	55	break;
	56	return p;
	57	}
	58
	59	/**
	60	* register_filesystem - register a new filesystem
	61	* @fs: the file system structure
	62	*
	63	* Adds the file system passed to the list of file systems the kernel
	64	* is aware of for mount and other syscalls. Returns 0 on success,
	65	* or a negative errno code on an error.
	66	*
	67	* The &struct file_system_type that is passed is linked into the kernel
	68	* structures and must not be freed until the file system has been
	69	* unregistered.
	70	*/
	71
	72	int register_filesystem(struct file_system_type * fs)
	73	{
	74	int res = 0;
	75	struct file_system_type ** p;
	76
3e1aeb00 DH	77	if (fs->parameters && !fs_validate_description(fs->parameters))
	78	return -EINVAL;
	79
79c0b2df	80	BUG_ON(strchr(fs->name, '.'));
1da177e4 LT	81	if (fs->next)
1da177e4 LT	82	return -EBUSY;
1da177e4	83	write_lock(&file_systems_lock);
79c0b2df	84	p = find_filesystem(fs->name, strlen(fs->name));
1da177e4 LT	85	if (*p)
	86	res = -EBUSY;
	87	else
	88	*p = fs;
	89	write_unlock(&file_systems_lock);
	90	return res;
	91	}
	92
	93	EXPORT_SYMBOL(register_filesystem);
	94
	95	/**
	96	* unregister_filesystem - unregister a file system
	97	* @fs: filesystem to unregister
	98	*
	99	* Remove a file system that was previously successfully registered
	100	* with the kernel. An error is returned if the file system is not found.
	101	* Zero is returned on a success.
	102	*
	103	* Once this function has returned the &struct file_system_type structure
	104	* may be freed or reused.
	105	*/
	106
	107	int unregister_filesystem(struct file_system_type * fs)
	108	{
	109	struct file_system_type ** tmp;
	110
	111	write_lock(&file_systems_lock);
	112	tmp = &file_systems;
	113	while (*tmp) {
	114	if (fs == *tmp) {
	115	*tmp = fs->next;
	116	fs->next = NULL;
	117	write_unlock(&file_systems_lock);
fff3e5ad	118	synchronize_rcu();
1da177e4 LT	119	return 0;
	120	}
	121	tmp = &(*tmp)->next;
	122	}
	123	write_unlock(&file_systems_lock);
31e6b01f	124
1da177e4 LT	125	return -EINVAL;
	126	}
	127
	128	EXPORT_SYMBOL(unregister_filesystem);
	129
6af9f7bf	130	#ifdef CONFIG_SYSFS_SYSCALL
1da177e4 LT	131	static int fs_index(const char __user * __name)
	132	{
	133	struct file_system_type * tmp;
91a27b2a	134	struct filename *name;
1da177e4 LT	135	int err, index;
	136
	137	name = getname(__name);
	138	err = PTR_ERR(name);
	139	if (IS_ERR(name))
	140	return err;
	141
	142	err = -EINVAL;
	143	read_lock(&file_systems_lock);
	144	for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
91a27b2a	145	if (strcmp(tmp->name, name->name) == 0) {
1da177e4 LT	146	err = index;
	147	break;
	148	}
	149	}
	150	read_unlock(&file_systems_lock);
	151	putname(name);
	152	return err;
	153	}
	154
	155	static int fs_name(unsigned int index, char __user * buf)
	156	{
	157	struct file_system_type * tmp;
	158	int len, res;
	159
	160	read_lock(&file_systems_lock);
	161	for (tmp = file_systems; tmp; tmp = tmp->next, index--)
	162	if (index <= 0 && try_module_get(tmp->owner))
	163	break;
	164	read_unlock(&file_systems_lock);
	165	if (!tmp)
	166	return -EINVAL;
	167
	168	/* OK, we got the reference, so we can safely block */
	169	len = strlen(tmp->name) + 1;
	170	res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
	171	put_filesystem(tmp);
	172	return res;
	173	}
	174
	175	static int fs_maxindex(void)
	176	{
	177	struct file_system_type * tmp;
	178	int index;
	179
	180	read_lock(&file_systems_lock);
	181	for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
	182	;
	183	read_unlock(&file_systems_lock);
	184	return index;
	185	}
	186
	187	/*
	188	* Whee.. Weird sysv syscall.
	189	*/
1e7bfb21	190	SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)
1da177e4 LT	191	{
	192	int retval = -EINVAL;
	193
	194	switch (option) {
	195	case 1:
	196	retval = fs_index((const char __user *) arg1);
	197	break;
	198
	199	case 2:
	200	retval = fs_name(arg1, (char __user *) arg2);
	201	break;
	202
	203	case 3:
	204	retval = fs_maxindex();
	205	break;
	206	}
	207	return retval;
	208	}
6af9f7bf	209	#endif
1da177e4	210
38e23c95	211	int __init get_filesystem_list(char *buf)
1da177e4 LT	212	{
	213	int len = 0;
	214	struct file_system_type * tmp;
	215
	216	read_lock(&file_systems_lock);
	217	tmp = file_systems;
	218	while (tmp && len < PAGE_SIZE - 80) {
	219	len += sprintf(buf+len, "%s\t%s\n",
	220	(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
	221	tmp->name);
	222	tmp = tmp->next;
	223	}
	224	read_unlock(&file_systems_lock);
	225	return len;
	226	}
	227
68274007 AD	228	#ifdef CONFIG_PROC_FS
	229	static int filesystems_proc_show(struct seq_file m, void v)
	230	{
	231	struct file_system_type * tmp;
	232
	233	read_lock(&file_systems_lock);
	234	tmp = file_systems;
	235	while (tmp) {
	236	seq_printf(m, "%s\t%s\n",
	237	(tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
	238	tmp->name);
	239	tmp = tmp->next;
	240	}
	241	read_unlock(&file_systems_lock);
	242	return 0;
	243	}
	244
68274007 AD	245	static int __init proc_filesystems_init(void)
68274007 AD	246	{
3f3942ac	247	proc_create_single("filesystems", 0, NULL, filesystems_proc_show);
68274007 AD	248	return 0;
	249	}
	250	module_init(proc_filesystems_init);
	251	#endif
	252
d8e9650d	253	static struct file_system_type __get_fs_type(const char name, int len)
1da177e4 LT	254	{
	255	struct file_system_type *fs;
	256
	257	read_lock(&file_systems_lock);
79c0b2df	258	fs = *(find_filesystem(name, len));
1da177e4 LT	259	if (fs && !try_module_get(fs->owner))
	260	fs = NULL;
	261	read_unlock(&file_systems_lock);
d8e9650d LZ	262	return fs;
	263	}
	264
	265	struct file_system_type get_fs_type(const char name)
	266	{
	267	struct file_system_type *fs;
	268	const char *dot = strchr(name, '.');
	269	int len = dot ? dot - name : strlen(name);
	270
	271	fs = __get_fs_type(name, len);
41124db8	272	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
d8e9650d	273	fs = __get_fs_type(name, len);
41124db8 LR	274	WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
41124db8 LR	275	}
79c0b2df MS	276
	277	if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {
	278	put_filesystem(fs);
	279	fs = NULL;
	280	}
1da177e4 LT	281	return fs;
	282	}
	283
	284	EXPORT_SYMBOL(get_fs_type);