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