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