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 write_lock(&file_systems_lock); 78 p = find_filesystem(fs->name, strlen(fs->name)); 79 if (*p) 80 res = -EBUSY; 81 else 82 *p = fs; 83 write_unlock(&file_systems_lock); 84 return res; 85 } 86 87 EXPORT_SYMBOL(register_filesystem); 88 89 /** 90 * unregister_filesystem - unregister a file system 91 * @fs: filesystem to unregister 92 * 93 * Remove a file system that was previously successfully registered 94 * with the kernel. An error is returned if the file system is not found. 95 * Zero is returned on a success. 96 * 97 * Once this function has returned the &struct file_system_type structure 98 * may be freed or reused. 99 */ 100 101 int unregister_filesystem(struct file_system_type * fs) 102 { 103 struct file_system_type ** tmp; 104 105 write_lock(&file_systems_lock); 106 tmp = &file_systems; 107 while (*tmp) { 108 if (fs == *tmp) { 109 *tmp = fs->next; 110 fs->next = NULL; 111 write_unlock(&file_systems_lock); 112 synchronize_rcu(); 113 return 0; 114 } 115 tmp = &(*tmp)->next; 116 } 117 write_unlock(&file_systems_lock); 118 119 return -EINVAL; 120 } 121 122 EXPORT_SYMBOL(unregister_filesystem); 123 124 static int fs_index(const char __user * __name) 125 { 126 struct file_system_type * tmp; 127 struct filename *name; 128 int err, index; 129 130 name = getname(__name); 131 err = PTR_ERR(name); 132 if (IS_ERR(name)) 133 return err; 134 135 err = -EINVAL; 136 read_lock(&file_systems_lock); 137 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) { 138 if (strcmp(tmp->name, name->name) == 0) { 139 err = index; 140 break; 141 } 142 } 143 read_unlock(&file_systems_lock); 144 putname(name); 145 return err; 146 } 147 148 static int fs_name(unsigned int index, char __user * buf) 149 { 150 struct file_system_type * tmp; 151 int len, res; 152 153 read_lock(&file_systems_lock); 154 for (tmp = file_systems; tmp; tmp = tmp->next, index--) 155 if (index <= 0 && try_module_get(tmp->owner)) 156 break; 157 read_unlock(&file_systems_lock); 158 if (!tmp) 159 return -EINVAL; 160 161 /* OK, we got the reference, so we can safely block */ 162 len = strlen(tmp->name) + 1; 163 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0; 164 put_filesystem(tmp); 165 return res; 166 } 167 168 static int fs_maxindex(void) 169 { 170 struct file_system_type * tmp; 171 int index; 172 173 read_lock(&file_systems_lock); 174 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++) 175 ; 176 read_unlock(&file_systems_lock); 177 return index; 178 } 179 180 /* 181 * Whee.. Weird sysv syscall. 182 */ 183 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2) 184 { 185 int retval = -EINVAL; 186 187 switch (option) { 188 case 1: 189 retval = fs_index((const char __user *) arg1); 190 break; 191 192 case 2: 193 retval = fs_name(arg1, (char __user *) arg2); 194 break; 195 196 case 3: 197 retval = fs_maxindex(); 198 break; 199 } 200 return retval; 201 } 202 203 int __init get_filesystem_list(char *buf) 204 { 205 int len = 0; 206 struct file_system_type * tmp; 207 208 read_lock(&file_systems_lock); 209 tmp = file_systems; 210 while (tmp && len < PAGE_SIZE - 80) { 211 len += sprintf(buf+len, "%s\t%s\n", 212 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", 213 tmp->name); 214 tmp = tmp->next; 215 } 216 read_unlock(&file_systems_lock); 217 return len; 218 } 219 220 #ifdef CONFIG_PROC_FS 221 static int filesystems_proc_show(struct seq_file *m, void *v) 222 { 223 struct file_system_type * tmp; 224 225 read_lock(&file_systems_lock); 226 tmp = file_systems; 227 while (tmp) { 228 seq_printf(m, "%s\t%s\n", 229 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", 230 tmp->name); 231 tmp = tmp->next; 232 } 233 read_unlock(&file_systems_lock); 234 return 0; 235 } 236 237 static int filesystems_proc_open(struct inode *inode, struct file *file) 238 { 239 return single_open(file, filesystems_proc_show, NULL); 240 } 241 242 static const struct file_operations filesystems_proc_fops = { 243 .open = filesystems_proc_open, 244 .read = seq_read, 245 .llseek = seq_lseek, 246 .release = single_release, 247 }; 248 249 static int __init proc_filesystems_init(void) 250 { 251 proc_create("filesystems", 0, NULL, &filesystems_proc_fops); 252 return 0; 253 } 254 module_init(proc_filesystems_init); 255 #endif 256 257 static struct file_system_type *__get_fs_type(const char *name, int len) 258 { 259 struct file_system_type *fs; 260 261 read_lock(&file_systems_lock); 262 fs = *(find_filesystem(name, len)); 263 if (fs && !try_module_get(fs->owner)) 264 fs = NULL; 265 read_unlock(&file_systems_lock); 266 return fs; 267 } 268 269 struct file_system_type *get_fs_type(const char *name) 270 { 271 struct file_system_type *fs; 272 const char *dot = strchr(name, '.'); 273 int len = dot ? dot - name : strlen(name); 274 275 fs = __get_fs_type(name, len); 276 if (!fs && (request_module("fs-%.*s", len, name) == 0)) 277 fs = __get_fs_type(name, len); 278 279 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) { 280 put_filesystem(fs); 281 fs = NULL; 282 } 283 return fs; 284 } 285 286 EXPORT_SYMBOL(get_fs_type); 287