fs/sysfs/mount.c

   1 /*
   2  * fs/sysfs/symlink.c - operations for initializing and mounting sysfs
   3  *
   4  * Copyright (c) 2001-3 Patrick Mochel
   5  * Copyright (c) 2007 SUSE Linux Products GmbH
   6  * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
   7  *
   8  * This file is released under the GPLv2.
   9  *
  10  * Please see Documentation/filesystems/sysfs.txt for more information.
  11  */
  12
  13 #define DEBUG
  14
  15 #include <linux/fs.h>
  16 #include <linux/mount.h>
  17 #include <linux/pagemap.h>
  18 #include <linux/init.h>
  19 #include <linux/module.h>
  20 #include <linux/magic.h>
  21 #include <linux/slab.h>
  22 #include <linux/user_namespace.h>
  23
  24 #include "sysfs.h"
  25
  26
  27 static struct vfsmount *sysfs_mnt;
  28 struct kmem_cache *sysfs_dir_cachep;
  29
  30 static const struct super_operations sysfs_ops = {
  31         .statfs         = simple_statfs,
  32         .drop_inode     = generic_delete_inode,
  33         .evict_inode    = sysfs_evict_inode,
  34 };
  35
  36 struct sysfs_dirent sysfs_root = {
  37         .s_name         = "",
  38         .s_count        = ATOMIC_INIT(1),
  39         .s_flags        = SYSFS_DIR,
  40         .s_mode         = S_IFDIR | S_IRUGO | S_IXUGO,
  41         .s_ino          = 1,
  42 };
  43
  44 static int sysfs_fill_super(struct super_block *sb, void *data, int silent)
  45 {
  46         struct inode *inode;
  47         struct dentry *root;
  48
  49         sb->s_blocksize = PAGE_CACHE_SIZE;
  50         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
  51         sb->s_magic = SYSFS_MAGIC;
  52         sb->s_op = &sysfs_ops;
  53         sb->s_time_gran = 1;
  54
  55         /* get root inode, initialize and unlock it */
  56         mutex_lock(&sysfs_mutex);
  57         inode = sysfs_get_inode(sb, &sysfs_root);
  58         mutex_unlock(&sysfs_mutex);
  59         if (!inode) {
  60                 pr_debug("sysfs: could not get root inode\n");
  61                 return -ENOMEM;
  62         }
  63
  64         /* instantiate and link root dentry */
  65         root = d_make_root(inode);
  66         if (!root) {
  67                 pr_debug("%s: could not get root dentry!\n", __func__);
  68                 return -ENOMEM;
  69         }
  70         root->d_fsdata = &sysfs_root;
  71         sb->s_root = root;
  72         sb->s_d_op = &sysfs_dentry_ops;
  73         return 0;
  74 }
  75
  76 static int sysfs_test_super(struct super_block *sb, void *data)
  77 {
  78         struct sysfs_super_info *sb_info = sysfs_info(sb);
  79         struct sysfs_super_info *info = data;
  80
  81         return sb_info->ns == info->ns;
  82 }
  83
  84 static int sysfs_set_super(struct super_block *sb, void *data)
  85 {
  86         int error;
  87         error = set_anon_super(sb, data);
  88         if (!error)
  89                 sb->s_fs_info = data;
  90         return error;
  91 }
  92
  93 static void free_sysfs_super_info(struct sysfs_super_info *info)
  94 {
  95         kobj_ns_drop(KOBJ_NS_TYPE_NET, info->ns);
  96         kfree(info);
  97 }
  98
  99 static struct dentry *sysfs_mount(struct file_system_type *fs_type,
 100         int flags, const char *dev_name, void *data)
 101 {
 102         struct sysfs_super_info *info;
 103         struct super_block *sb;
 104         int error;
 105
 106         if (!(flags & MS_KERNMOUNT)) {
 107                 if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
 108                         return ERR_PTR(-EPERM);
 109
 110                 if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))
 111                         return ERR_PTR(-EPERM);
 112         }
 113
 114         info = kzalloc(sizeof(*info), GFP_KERNEL);
 115         if (!info)
 116                 return ERR_PTR(-ENOMEM);
 117
 118         info->ns = kobj_ns_grab_current(KOBJ_NS_TYPE_NET);
 119
 120         sb = sget(fs_type, sysfs_test_super, sysfs_set_super, flags, info);
 121         if (IS_ERR(sb) || sb->s_fs_info != info)
 122                 free_sysfs_super_info(info);
 123         if (IS_ERR(sb))
 124                 return ERR_CAST(sb);
 125         if (!sb->s_root) {
 126                 error = sysfs_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
 127                 if (error) {
 128                         deactivate_locked_super(sb);
 129                         return ERR_PTR(error);
 130                 }
 131                 sb->s_flags |= MS_ACTIVE;
 132         }
 133
 134         return dget(sb->s_root);
 135 }
 136
 137 static void sysfs_kill_sb(struct super_block *sb)
 138 {
 139         struct sysfs_super_info *info = sysfs_info(sb);
 140         /* Remove the superblock from fs_supers/s_instances
 141          * so we can't find it, before freeing sysfs_super_info.
 142          */
 143         kill_anon_super(sb);
 144         free_sysfs_super_info(info);
 145 }
 146
 147 static struct file_system_type sysfs_fs_type = {
 148         .name           = "sysfs",
 149         .mount          = sysfs_mount,
 150         .kill_sb        = sysfs_kill_sb,
 151         .fs_flags       = FS_USERNS_MOUNT,
 152 };
 153
 154 int __init sysfs_init(void)
 155 {
 156         int err = -ENOMEM;
 157
 158         sysfs_dir_cachep = kmem_cache_create("sysfs_dir_cache",
 159                                               sizeof(struct sysfs_dirent),
 160                                               0, 0, NULL);
 161         if (!sysfs_dir_cachep)
 162                 goto out;
 163
 164         err = sysfs_inode_init();
 165         if (err)
 166                 goto out_err;
 167
 168         err = register_filesystem(&sysfs_fs_type);
 169         if (!err) {
 170                 sysfs_mnt = kern_mount(&sysfs_fs_type);
 171                 if (IS_ERR(sysfs_mnt)) {
 172                         printk(KERN_ERR "sysfs: could not mount!\n");
 173                         err = PTR_ERR(sysfs_mnt);
 174                         sysfs_mnt = NULL;
 175                         unregister_filesystem(&sysfs_fs_type);
 176                         goto out_err;
 177                 }
 178         } else
 179                 goto out_err;
 180 out:
 181         return err;
 182 out_err:
 183         kmem_cache_destroy(sysfs_dir_cachep);
 184         sysfs_dir_cachep = NULL;
 185         goto out;
 186 }
 187
 188 #undef sysfs_get
 189 struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd)
 190 {
 191         return __sysfs_get(sd);
 192 }
 193 EXPORT_SYMBOL_GPL(sysfs_get);
 194
 195 #undef sysfs_put
 196 void sysfs_put(struct sysfs_dirent *sd)
 197 {
 198         __sysfs_put(sd);
 199 }
 200 EXPORT_SYMBOL_GPL(sysfs_put);