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1// SPDX-License-Identifier: GPL-2.02/*3 * linux/fs/filesystems.c4 *5 * Copyright (C) 1991, 1992 Linus Torvalds6 *7 * table of configured filesystems8 */9 10#include <linux/syscalls.h>11#include <linux/fs.h>12#include <linux/proc_fs.h>13#include <linux/seq_file.h>14#include <linux/kmod.h>15#include <linux/init.h>16#include <linux/module.h>17#include <linux/slab.h>18#include <linux/uaccess.h>19#include <linux/fs_parser.h>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 or28 * 2) we hold the reference to the module.29 * The latter can be guaranteed by call of try_module_get(); if it30 * 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 34static struct file_system_type *file_systems;35static DEFINE_RWLOCK(file_systems_lock);36 37/* WARNING: This can be used only if we _already_ own a reference */38struct file_system_type *get_filesystem(struct file_system_type *fs)39{40 __module_get(fs->owner);41 return fs;42}43 44void put_filesystem(struct file_system_type *fs)45{46 module_put(fs->owner);47}48 49static struct file_system_type **find_filesystem(const char *name, unsigned len)50{51 struct file_system_type **p;52 for (p = &file_systems; *p; p = &(*p)->next)53 if (strncmp((*p)->name, name, len) == 0 &&54 !(*p)->name[len])55 break;56 return p;57}58 59/**60 * register_filesystem - register a new filesystem61 * @fs: the file system structure62 *63 * Adds the file system passed to the list of file systems the kernel64 * 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 been69 * unregistered.70 */71 72int register_filesystem(struct file_system_type * fs)73{74 int res = 0;75 struct file_system_type ** p;76 77 if (fs->parameters &&78 !fs_validate_description(fs->name, fs->parameters))79 return -EINVAL;80 81 BUG_ON(strchr(fs->name, '.'));82 if (fs->next)83 return -EBUSY;84 write_lock(&file_systems_lock);85 p = find_filesystem(fs->name, strlen(fs->name));86 if (*p)87 res = -EBUSY;88 else89 *p = fs;90 write_unlock(&file_systems_lock);91 return res;92}93 94EXPORT_SYMBOL(register_filesystem);95 96/**97 * unregister_filesystem - unregister a file system98 * @fs: filesystem to unregister99 *100 * Remove a file system that was previously successfully registered101 * with the kernel. An error is returned if the file system is not found.102 * Zero is returned on a success.103 * 104 * Once this function has returned the &struct file_system_type structure105 * may be freed or reused.106 */107 108int unregister_filesystem(struct file_system_type * fs)109{110 struct file_system_type ** tmp;111 112 write_lock(&file_systems_lock);113 tmp = &file_systems;114 while (*tmp) {115 if (fs == *tmp) {116 *tmp = fs->next;117 fs->next = NULL;118 write_unlock(&file_systems_lock);119 synchronize_rcu();120 return 0;121 }122 tmp = &(*tmp)->next;123 }124 write_unlock(&file_systems_lock);125 126 return -EINVAL;127}128 129EXPORT_SYMBOL(unregister_filesystem);130 131#ifdef CONFIG_SYSFS_SYSCALL132static int fs_index(const char __user * __name)133{134 struct file_system_type * tmp;135 struct filename *name;136 int err, index;137 138 name = getname(__name);139 err = PTR_ERR(name);140 if (IS_ERR(name))141 return err;142 143 err = -EINVAL;144 read_lock(&file_systems_lock);145 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {146 if (strcmp(tmp->name, name->name) == 0) {147 err = index;148 break;149 }150 }151 read_unlock(&file_systems_lock);152 putname(name);153 return err;154}155 156static int fs_name(unsigned int index, char __user * buf)157{158 struct file_system_type * tmp;159 int len, res;160 161 read_lock(&file_systems_lock);162 for (tmp = file_systems; tmp; tmp = tmp->next, index--)163 if (index <= 0 && try_module_get(tmp->owner))164 break;165 read_unlock(&file_systems_lock);166 if (!tmp)167 return -EINVAL;168 169 /* OK, we got the reference, so we can safely block */170 len = strlen(tmp->name) + 1;171 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;172 put_filesystem(tmp);173 return res;174}175 176static int fs_maxindex(void)177{178 struct file_system_type * tmp;179 int index;180 181 read_lock(&file_systems_lock);182 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)183 ;184 read_unlock(&file_systems_lock);185 return index;186}187 188/*189 * Whee.. Weird sysv syscall. 190 */191SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2)192{193 int retval = -EINVAL;194 195 switch (option) {196 case 1:197 retval = fs_index((const char __user *) arg1);198 break;199 200 case 2:201 retval = fs_name(arg1, (char __user *) arg2);202 break;203 204 case 3:205 retval = fs_maxindex();206 break;207 }208 return retval;209}210#endif211 212int __init list_bdev_fs_names(char *buf, size_t size)213{214 struct file_system_type *p;215 size_t len;216 int count = 0;217 218 read_lock(&file_systems_lock);219 for (p = file_systems; p; p = p->next) {220 if (!(p->fs_flags & FS_REQUIRES_DEV))221 continue;222 len = strlen(p->name) + 1;223 if (len > size) {224 pr_warn("%s: truncating file system list\n", __func__);225 break;226 }227 memcpy(buf, p->name, len);228 buf += len;229 size -= len;230 count++;231 }232 read_unlock(&file_systems_lock);233 return count;234}235 236#ifdef CONFIG_PROC_FS237static int filesystems_proc_show(struct seq_file *m, void *v)238{239 struct file_system_type * tmp;240 241 read_lock(&file_systems_lock);242 tmp = file_systems;243 while (tmp) {244 seq_printf(m, "%s\t%s\n",245 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",246 tmp->name);247 tmp = tmp->next;248 }249 read_unlock(&file_systems_lock);250 return 0;251}252 253static int __init proc_filesystems_init(void)254{255 proc_create_single("filesystems", 0, NULL, filesystems_proc_show);256 return 0;257}258module_init(proc_filesystems_init);259#endif260 261static struct file_system_type *__get_fs_type(const char *name, int len)262{263 struct file_system_type *fs;264 265 read_lock(&file_systems_lock);266 fs = *(find_filesystem(name, len));267 if (fs && !try_module_get(fs->owner))268 fs = NULL;269 read_unlock(&file_systems_lock);270 return fs;271}272 273struct file_system_type *get_fs_type(const char *name)274{275 struct file_system_type *fs;276 const char *dot = strchr(name, '.');277 int len = dot ? dot - name : strlen(name);278 279 fs = __get_fs_type(name, len);280 if (!fs && (request_module("fs-%.*s", len, name) == 0)) {281 fs = __get_fs_type(name, len);282 if (!fs)283 pr_warn_once("request_module fs-%.*s succeeded, but still no fs?\n",284 len, name);285 }286 287 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {288 put_filesystem(fs);289 fs = NULL;290 }291 return fs;292}293 294EXPORT_SYMBOL(get_fs_type);295