1 /* 2 * linux/fs/filesystems.c 3 * 4 * Copyright (C) 1991, 1992 Linus Torvalds 5 * 6 * table of configured filesystems 7 */ 8 9 #include <linux/syscalls.h> 10 #include <linux/fs.h> 11 #include <linux/proc_fs.h> 12 #include <linux/seq_file.h> 13 #include <linux/kmod.h> 14 #include <linux/init.h> 15 #include <linux/module.h> 16 #include <linux/slab.h> 17 #include <asm/uaccess.h> 18 19 /* 20 * Handling of filesystem drivers list. 21 * Rules: 22 * Inclusion to/removals from/scanning of list are protected by spinlock. 23 * During the unload module must call unregister_filesystem(). 24 * We can access the fields of list element if: 25 * 1) spinlock is held or 26 * 2) we hold the reference to the module. 27 * The latter can be guaranteed by call of try_module_get(); if it 28 * returned 0 we must skip the element, otherwise we got the reference. 29 * Once the reference is obtained we can drop the spinlock. 30 */ 31 32 static struct file_system_type *file_systems; 33 static DEFINE_RWLOCK(file_systems_lock); 34 35 /* WARNING: This can be used only if we _already_ own a reference */ 36 void get_filesystem(struct file_system_type *fs) 37 { 38 __module_get(fs->owner); 39 } 40 41 void put_filesystem(struct file_system_type *fs) 42 { 43 module_put(fs->owner); 44 } 45 46 static struct file_system_type **find_filesystem(const char *name, unsigned len) 47 { 48 struct file_system_type **p; 49 for (p=&file_systems; *p; p=&(*p)->next) 50 if (strlen((*p)->name) == len && 51 strncmp((*p)->name, name, len) == 0) 52 break; 53 return p; 54 } 55 56 /** 57 * register_filesystem - register a new filesystem 58 * @fs: the file system structure 59 * 60 * Adds the file system passed to the list of file systems the kernel 61 * is aware of for mount and other syscalls. Returns 0 on success, 62 * or a negative errno code on an error. 63 * 64 * The &struct file_system_type that is passed is linked into the kernel 65 * structures and must not be freed until the file system has been 66 * unregistered. 67 */ 68 69 int register_filesystem(struct file_system_type * fs) 70 { 71 int res = 0; 72 struct file_system_type ** p; 73 74 BUG_ON(strchr(fs->name, '.')); 75 if (fs->next) 76 return -EBUSY; 77 INIT_LIST_HEAD(&fs->fs_supers); 78 write_lock(&file_systems_lock); 79 p = find_filesystem(fs->name, strlen(fs->name)); 80 if (*p) 81 res = -EBUSY; 82 else 83 *p = fs; 84 write_unlock(&file_systems_lock); 85 return res; 86 } 87 88 EXPORT_SYMBOL(register_filesystem); 89 90 /** 91 * unregister_filesystem - unregister a file system 92 * @fs: filesystem to unregister 93 * 94 * Remove a file system that was previously successfully registered 95 * with the kernel. An error is returned if the file system is not found. 96 * Zero is returned on a success. 97 * 98 * Once this function has returned the &struct file_system_type structure 99 * may be freed or reused. 100 */ 101 102 int unregister_filesystem(struct file_system_type * fs) 103 { 104 struct file_system_type ** tmp; 105 106 write_lock(&file_systems_lock); 107 tmp = &file_systems; 108 while (*tmp) { 109 if (fs == *tmp) { 110 *tmp = fs->next; 111 fs->next = NULL; 112 write_unlock(&file_systems_lock); 113 return 0; 114 } 115 tmp = &(*tmp)->next; 116 } 117 write_unlock(&file_systems_lock); 118 119 synchronize_rcu(); 120 121 return -EINVAL; 122 } 123 124 EXPORT_SYMBOL(unregister_filesystem); 125 126 static int fs_index(const char __user * __name) 127 { 128 struct file_system_type * tmp; 129 char * name; 130 int err, index; 131 132 name = getname(__name); 133 err = PTR_ERR(name); 134 if (IS_ERR(name)) 135 return err; 136 137 err = -EINVAL; 138 read_lock(&file_systems_lock); 139 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) { 140 if (strcmp(tmp->name,name) == 0) { 141 err = index; 142 break; 143 } 144 } 145 read_unlock(&file_systems_lock); 146 putname(name); 147 return err; 148 } 149 150 static int fs_name(unsigned int index, char __user * buf) 151 { 152 struct file_system_type * tmp; 153 int len, res; 154 155 read_lock(&file_systems_lock); 156 for (tmp = file_systems; tmp; tmp = tmp->next, index--) 157 if (index <= 0 && try_module_get(tmp->owner)) 158 break; 159 read_unlock(&file_systems_lock); 160 if (!tmp) 161 return -EINVAL; 162 163 /* OK, we got the reference, so we can safely block */ 164 len = strlen(tmp->name) + 1; 165 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0; 166 put_filesystem(tmp); 167 return res; 168 } 169 170 static int fs_maxindex(void) 171 { 172 struct file_system_type * tmp; 173 int index; 174 175 read_lock(&file_systems_lock); 176 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++) 177 ; 178 read_unlock(&file_systems_lock); 179 return index; 180 } 181 182 /* 183 * Whee.. Weird sysv syscall. 184 */ 185 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2) 186 { 187 int retval = -EINVAL; 188 189 switch (option) { 190 case 1: 191 retval = fs_index((const char __user *) arg1); 192 break; 193 194 case 2: 195 retval = fs_name(arg1, (char __user *) arg2); 196 break; 197 198 case 3: 199 retval = fs_maxindex(); 200 break; 201 } 202 return retval; 203 } 204 205 int __init get_filesystem_list(char *buf) 206 { 207 int len = 0; 208 struct file_system_type * tmp; 209 210 read_lock(&file_systems_lock); 211 tmp = file_systems; 212 while (tmp && len < PAGE_SIZE - 80) { 213 len += sprintf(buf+len, "%s\t%s\n", 214 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", 215 tmp->name); 216 tmp = tmp->next; 217 } 218 read_unlock(&file_systems_lock); 219 return len; 220 } 221 222 #ifdef CONFIG_PROC_FS 223 static int filesystems_proc_show(struct seq_file *m, void *v) 224 { 225 struct file_system_type * tmp; 226 227 read_lock(&file_systems_lock); 228 tmp = file_systems; 229 while (tmp) { 230 seq_printf(m, "%s\t%s\n", 231 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", 232 tmp->name); 233 tmp = tmp->next; 234 } 235 read_unlock(&file_systems_lock); 236 return 0; 237 } 238 239 static int filesystems_proc_open(struct inode *inode, struct file *file) 240 { 241 return single_open(file, filesystems_proc_show, NULL); 242 } 243 244 static const struct file_operations filesystems_proc_fops = { 245 .open = filesystems_proc_open, 246 .read = seq_read, 247 .llseek = seq_lseek, 248 .release = single_release, 249 }; 250 251 static int __init proc_filesystems_init(void) 252 { 253 proc_create("filesystems", 0, NULL, &filesystems_proc_fops); 254 return 0; 255 } 256 module_init(proc_filesystems_init); 257 #endif 258 259 static struct file_system_type *__get_fs_type(const char *name, int len) 260 { 261 struct file_system_type *fs; 262 263 read_lock(&file_systems_lock); 264 fs = *(find_filesystem(name, len)); 265 if (fs && !try_module_get(fs->owner)) 266 fs = NULL; 267 read_unlock(&file_systems_lock); 268 return fs; 269 } 270 271 struct file_system_type *get_fs_type(const char *name) 272 { 273 struct file_system_type *fs; 274 const char *dot = strchr(name, '.'); 275 int len = dot ? dot - name : strlen(name); 276 277 fs = __get_fs_type(name, len); 278 if (!fs && (request_module("%.*s", len, name) == 0)) 279 fs = __get_fs_type(name, len); 280 281 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) { 282 put_filesystem(fs); 283 fs = NULL; 284 } 285 return fs; 286 } 287 288 EXPORT_SYMBOL(get_fs_type); 289