fs/filesystems.c

   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/fs.h>
  10 #include <linux/slab.h>
  11 #include <linux/kmod.h>
  12 #include <linux/init.h>
  13 #include <linux/module.h>
  14 #include <asm/uaccess.h>
  15
  16 /*
  17  * Handling of filesystem drivers list.
  18  * Rules:
  19  *      Inclusion to/removals from/scanning of list are protected by spinlock.
  20  *      During the unload module must call unregister_filesystem().
  21  *      We can access the fields of list element if:
  22  *              1) spinlock is held or
  23  *              2) we hold the reference to the module.
  24  *      The latter can be guaranteed by call of try_module_get(); if it
  25  *      returned 0 we must skip the element, otherwise we got the reference.
  26  *      Once the reference is obtained we can drop the spinlock.
  27  */
  28
  29 static struct file_system_type *file_systems;
  30 static rwlock_t file_systems_lock = RW_LOCK_UNLOCKED;
  31
  32 /* WARNING: This can be used only if we _already_ own a reference */
  33 void get_filesystem(struct file_system_type *fs)
  34 {
  35         __module_get(fs->owner);
  36 }
  37
  38 void put_filesystem(struct file_system_type *fs)
  39 {
  40         module_put(fs->owner);
  41 }
  42
  43 static struct file_system_type **find_filesystem(const char *name)
  44 {
  45         struct file_system_type **p;
  46         for (p=&file_systems; *p; p=&(*p)->next)
  47                 if (strcmp((*p)->name,name) == 0)
  48                         break;
  49         return p;
  50 }
  51
  52 /**
  53  *      register_filesystem - register a new filesystem
  54  *      @fs: the file system structure
  55  *
  56  *      Adds the file system passed to the list of file systems the kernel
  57  *      is aware of for mount and other syscalls. Returns 0 on success,
  58  *      or a negative errno code on an error.
  59  *
  60  *      The &struct file_system_type that is passed is linked into the kernel
  61  *      structures and must not be freed until the file system has been
  62  *      unregistered.
  63  */
  64
  65 int register_filesystem(struct file_system_type * fs)
  66 {
  67         int res = 0;
  68         struct file_system_type ** p;
  69
  70         if (!fs)
  71                 return -EINVAL;
  72         if (fs->next)
  73                 return -EBUSY;
  74         INIT_LIST_HEAD(&fs->fs_supers);
  75         write_lock(&file_systems_lock);
  76         p = find_filesystem(fs->name);
  77         if (*p)
  78                 res = -EBUSY;
  79         else
  80                 *p = fs;
  81         write_unlock(&file_systems_lock);
  82         return res;
  83 }
  84
  85 /**
  86  *      unregister_filesystem - unregister a file system
  87  *      @fs: filesystem to unregister
  88  *
  89  *      Remove a file system that was previously successfully registered
  90  *      with the kernel. An error is returned if the file system is not found.
  91  *      Zero is returned on a success.
  92  *
  93  *      Once this function has returned the &struct file_system_type structure
  94  *      may be freed or reused.
  95  */
  96
  97 int unregister_filesystem(struct file_system_type * fs)
  98 {
  99         struct file_system_type ** tmp;
 100
 101         write_lock(&file_systems_lock);
 102         tmp = &file_systems;
 103         while (*tmp) {
 104                 if (fs == *tmp) {
 105                         *tmp = fs->next;
 106                         fs->next = NULL;
 107                         write_unlock(&file_systems_lock);
 108                         return 0;
 109                 }
 110                 tmp = &(*tmp)->next;
 111         }
 112         write_unlock(&file_systems_lock);
 113         return -EINVAL;
 114 }
 115
 116 static int fs_index(const char __user * __name)
 117 {
 118         struct file_system_type * tmp;
 119         char * name;
 120         int err, index;
 121
 122         name = getname(__name);
 123         err = PTR_ERR(name);
 124         if (IS_ERR(name))
 125                 return err;
 126
 127         err = -EINVAL;
 128         read_lock(&file_systems_lock);
 129         for (tmp=file_systems, index=0 ; tmp ; tmp=tmp->next, index++) {
 130                 if (strcmp(tmp->name,name) == 0) {
 131                         err = index;
 132                         break;
 133                 }
 134         }
 135         read_unlock(&file_systems_lock);
 136         putname(name);
 137         return err;
 138 }
 139
 140 static int fs_name(unsigned int index, char __user * buf)
 141 {
 142         struct file_system_type * tmp;
 143         int len, res;
 144
 145         read_lock(&file_systems_lock);
 146         for (tmp = file_systems; tmp; tmp = tmp->next, index--)
 147                 if (index <= 0 && try_module_get(tmp->owner))
 148                         break;
 149         read_unlock(&file_systems_lock);
 150         if (!tmp)
 151                 return -EINVAL;
 152
 153         /* OK, we got the reference, so we can safely block */
 154         len = strlen(tmp->name) + 1;
 155         res = copy_to_user(buf, tmp->name, len) ? -EFAULT : 0;
 156         put_filesystem(tmp);
 157         return res;
 158 }
 159
 160 static int fs_maxindex(void)
 161 {
 162         struct file_system_type * tmp;
 163         int index;
 164
 165         read_lock(&file_systems_lock);
 166         for (tmp = file_systems, index = 0 ; tmp ; tmp = tmp->next, index++)
 167                 ;
 168         read_unlock(&file_systems_lock);
 169         return index;
 170 }
 171
 172 /*
 173  * Whee.. Weird sysv syscall.
 174  */
 175 asmlinkage long sys_sysfs(int option, unsigned long arg1, unsigned long arg2)
 176 {
 177         int retval = -EINVAL;
 178
 179         switch (option) {
 180                 case 1:
 181                         retval = fs_index((const char __user *) arg1);
 182                         break;
 183
 184                 case 2:
 185                         retval = fs_name(arg1, (char __user *) arg2);
 186                         break;
 187
 188                 case 3:
 189                         retval = fs_maxindex();
 190                         break;
 191         }
 192         return retval;
 193 }
 194
 195 int get_filesystem_list(char * buf)
 196 {
 197         int len = 0;
 198         struct file_system_type * tmp;
 199
 200         read_lock(&file_systems_lock);
 201         tmp = file_systems;
 202         while (tmp && len < PAGE_SIZE - 80) {
 203                 len += sprintf(buf+len, "%s\t%s\n",
 204                         (tmp->fs_flags & FS_REQUIRES_DEV) ? "" : "nodev",
 205                         tmp->name);
 206                 tmp = tmp->next;
 207         }
 208         read_unlock(&file_systems_lock);
 209         return len;
 210 }
 211
 212 struct file_system_type *get_fs_type(const char *name)
 213 {
 214         struct file_system_type *fs;
 215
 216         read_lock(&file_systems_lock);
 217         fs = *(find_filesystem(name));
 218         if (fs && !try_module_get(fs->owner))
 219                 fs = NULL;
 220         read_unlock(&file_systems_lock);
 221         if (!fs && (request_module("%s", name) == 0)) {
 222                 read_lock(&file_systems_lock);
 223                 fs = *(find_filesystem(name));
 224                 if (fs && !try_module_get(fs->owner))
 225                         fs = NULL;
 226                 read_unlock(&file_systems_lock);
 227         }
 228         return fs;
 229 }