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/slab.h> 14 #include <linux/kmod.h> 15 #include <linux/init.h> 16 #include <linux/module.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 return -EINVAL; 119 } 120 121 EXPORT_SYMBOL(unregister_filesystem); 122 123 static int fs_index(const char __user * __name) 124 { 125 struct file_system_type * tmp; 126 char * name; 127 int err, index; 128 129 name = getname(__name); 130 err = PTR_ERR(name); 131 if (IS_ERR(name)) 132 return err; 133 134 err = -EINVAL; 135 read_lock(&file_systems_lock); 136 for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) { 137 if (strcmp(tmp->name,name) == 0) { 138 err = index; 139 break; 140 } 141 } 142 read_unlock(&file_systems_lock); 143 putname(name); 144 return err; 145 } 146 147 static int fs_name(unsigned int index, char __user * buf) 148 { 149 struct file_system_type * tmp; 150 int len, res; 151 152 read_lock(&file_systems_lock); 153 for (tmp = file_systems; tmp; tmp = tmp->next, index--) 154 if (index <= 0 && try_module_get(tmp->owner)) 155 break; 156 read_unlock(&file_systems_lock); 157 if (!tmp) 158 return -EINVAL; 159 160 /* OK, we got the reference, so we can safely block */ 161 len = strlen(tmp->name) + 1; 162 res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0; 163 put_filesystem(tmp); 164 return res; 165 } 166 167 static int fs_maxindex(void) 168 { 169 struct file_system_type * tmp; 170 int index; 171 172 read_lock(&file_systems_lock); 173 for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++) 174 ; 175 read_unlock(&file_systems_lock); 176 return index; 177 } 178 179 /* 180 * Whee.. Weird sysv syscall. 181 */ 182 SYSCALL_DEFINE3(sysfs, int, option, unsigned long, arg1, unsigned long, arg2) 183 { 184 int retval = -EINVAL; 185 186 switch (option) { 187 case 1: 188 retval = fs_index((const char __user *) arg1); 189 break; 190 191 case 2: 192 retval = fs_name(arg1, (char __user *) arg2); 193 break; 194 195 case 3: 196 retval = fs_maxindex(); 197 break; 198 } 199 return retval; 200 } 201 202 int get_filesystem_list(char * buf) 203 { 204 int len = 0; 205 struct file_system_type * tmp; 206 207 read_lock(&file_systems_lock); 208 tmp = file_systems; 209 while (tmp && len < PAGE_SIZE - 80) { 210 len += sprintf(buf+len, "%s\t%s\n", 211 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", 212 tmp->name); 213 tmp = tmp->next; 214 } 215 read_unlock(&file_systems_lock); 216 return len; 217 } 218 219 #ifdef CONFIG_PROC_FS 220 static int filesystems_proc_show(struct seq_file *m, void *v) 221 { 222 struct file_system_type * tmp; 223 224 read_lock(&file_systems_lock); 225 tmp = file_systems; 226 while (tmp) { 227 seq_printf(m, "%s\t%s\n", 228 (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev", 229 tmp->name); 230 tmp = tmp->next; 231 } 232 read_unlock(&file_systems_lock); 233 return 0; 234 } 235 236 static int filesystems_proc_open(struct inode *inode, struct file *file) 237 { 238 return single_open(file, filesystems_proc_show, NULL); 239 } 240 241 static const struct file_operations filesystems_proc_fops = { 242 .open = filesystems_proc_open, 243 .read = seq_read, 244 .llseek = seq_lseek, 245 .release = single_release, 246 }; 247 248 static int __init proc_filesystems_init(void) 249 { 250 proc_create("filesystems", 0, NULL, &filesystems_proc_fops); 251 return 0; 252 } 253 module_init(proc_filesystems_init); 254 #endif 255 256 static struct file_system_type *__get_fs_type(const char *name, int len) 257 { 258 struct file_system_type *fs; 259 260 read_lock(&file_systems_lock); 261 fs = *(find_filesystem(name, len)); 262 if (fs && !try_module_get(fs->owner)) 263 fs = NULL; 264 read_unlock(&file_systems_lock); 265 return fs; 266 } 267 268 struct file_system_type *get_fs_type(const char *name) 269 { 270 struct file_system_type *fs; 271 const char *dot = strchr(name, '.'); 272 int len = dot ? dot - name : strlen(name); 273 274 fs = __get_fs_type(name, len); 275 if (!fs && (request_module("%.*s", len, name) == 0)) 276 fs = __get_fs_type(name, len); 277 278 if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) { 279 put_filesystem(fs); 280 fs = NULL; 281 } 282 return fs; 283 } 284 285 EXPORT_SYMBOL(get_fs_type); 286