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 | (KOBJ_NS_TYPE_NONE << SYSFS_NS_TYPE_SHIFT),
  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         enum kobj_ns_type type;
  81         int found = 1;
  82
  83         for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++) {
  84                 if (sb_info->ns[type] != info->ns[type])
  85                         found = 0;
  86         }
  87         return found;
  88 }
  89
  90 static int sysfs_set_super(struct super_block *sb, void *data)
  91 {
  92         int error;
  93         error = set_anon_super(sb, data);
  94         if (!error)
  95                 sb->s_fs_info = data;
  96         return error;
  97 }
  98
  99 static void free_sysfs_super_info(struct sysfs_super_info *info)
 100 {
 101         int type;
 102         for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++)
 103                 kobj_ns_drop(type, info->ns[type]);
 104         kfree(info);
 105 }
 106
 107 static struct dentry *sysfs_mount(struct file_system_type *fs_type,
 108         int flags, const char *dev_name, void *data)
 109 {
 110         struct sysfs_super_info *info;
 111         enum kobj_ns_type type;
 112         struct super_block *sb;
 113         int error;
 114
 115         if (!(flags & MS_KERNMOUNT)) {
 116                 if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))
 117                         return ERR_PTR(-EPERM);
 118
 119                 for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++) {
 120                         if (!kobj_ns_current_may_mount(type))
 121                                 return ERR_PTR(-EPERM);
 122                 }
 123         }
 124
 125         info = kzalloc(sizeof(*info), GFP_KERNEL);
 126         if (!info)
 127                 return ERR_PTR(-ENOMEM);
 128
 129         for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++)
 130                 info->ns[type] = kobj_ns_grab_current(type);
 131
 132         sb = sget(fs_type, sysfs_test_super, sysfs_set_super, flags, info);
 133         if (IS_ERR(sb) || sb->s_fs_info != info)
 134                 free_sysfs_super_info(info);
 135         if (IS_ERR(sb))
 136                 return ERR_CAST(sb);
 137         if (!sb->s_root) {
 138                 error = sysfs_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
 139                 if (error) {
 140                         deactivate_locked_super(sb);
 141                         return ERR_PTR(error);
 142                 }
 143                 sb->s_flags |= MS_ACTIVE;
 144         }
 145
 146         return dget(sb->s_root);
 147 }
 148
 149 static void sysfs_kill_sb(struct super_block *sb)
 150 {
 151         struct sysfs_super_info *info = sysfs_info(sb);
 152         /* Remove the superblock from fs_supers/s_instances
 153          * so we can't find it, before freeing sysfs_super_info.
 154          */
 155         kill_anon_super(sb);
 156         free_sysfs_super_info(info);
 157 }
 158
 159 static struct file_system_type sysfs_fs_type = {
 160         .name           = "sysfs",
 161         .mount          = sysfs_mount,
 162         .kill_sb        = sysfs_kill_sb,
 163         .fs_flags       = FS_USERNS_MOUNT,
 164 };
 165
 166 int __init sysfs_init(void)
 167 {
 168         int err = -ENOMEM;
 169
 170         sysfs_dir_cachep = kmem_cache_create("sysfs_dir_cache",
 171                                               sizeof(struct sysfs_dirent),
 172                                               0, 0, NULL);
 173         if (!sysfs_dir_cachep)
 174                 goto out;
 175
 176         err = sysfs_inode_init();
 177         if (err)
 178                 goto out_err;
 179
 180         err = register_filesystem(&sysfs_fs_type);
 181         if (!err) {
 182                 sysfs_mnt = kern_mount(&sysfs_fs_type);
 183                 if (IS_ERR(sysfs_mnt)) {
 184                         printk(KERN_ERR "sysfs: could not mount!\n");
 185                         err = PTR_ERR(sysfs_mnt);
 186                         sysfs_mnt = NULL;
 187                         unregister_filesystem(&sysfs_fs_type);
 188                         goto out_err;
 189                 }
 190         } else
 191                 goto out_err;
 192 out:
 193         return err;
 194 out_err:
 195         kmem_cache_destroy(sysfs_dir_cachep);
 196         sysfs_dir_cachep = NULL;
 197         goto out;
 198 }
 199
 200 #undef sysfs_get
 201 struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd)
 202 {
 203         return __sysfs_get(sd);
 204 }
 205 EXPORT_SYMBOL_GPL(sysfs_get);
 206
 207 #undef sysfs_put
 208 void sysfs_put(struct sysfs_dirent *sd)
 209 {
 210         __sysfs_put(sd);
 211 }
 212 EXPORT_SYMBOL_GPL(sysfs_put);