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) && !current_user_ns()->may_mount_sysfs)
 116                 return ERR_PTR(-EPERM);
 117
 118         info = kzalloc(sizeof(*info), GFP_KERNEL);
 119         if (!info)
 120                 return ERR_PTR(-ENOMEM);
 121
 122         for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++)
 123                 info->ns[type] = kobj_ns_grab_current(type);
 124
 125         sb = sget(fs_type, sysfs_test_super, sysfs_set_super, flags, info);
 126         if (IS_ERR(sb) || sb->s_fs_info != info)
 127                 free_sysfs_super_info(info);
 128         if (IS_ERR(sb))
 129                 return ERR_CAST(sb);
 130         if (!sb->s_root) {
 131                 error = sysfs_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
 132                 if (error) {
 133                         deactivate_locked_super(sb);
 134                         return ERR_PTR(error);
 135                 }
 136                 sb->s_flags |= MS_ACTIVE;
 137         }
 138
 139         return dget(sb->s_root);
 140 }
 141
 142 static void sysfs_kill_sb(struct super_block *sb)
 143 {
 144         struct sysfs_super_info *info = sysfs_info(sb);
 145         /* Remove the superblock from fs_supers/s_instances
 146          * so we can't find it, before freeing sysfs_super_info.
 147          */
 148         kill_anon_super(sb);
 149         free_sysfs_super_info(info);
 150 }
 151
 152 static struct file_system_type sysfs_fs_type = {
 153         .name           = "sysfs",
 154         .mount          = sysfs_mount,
 155         .kill_sb        = sysfs_kill_sb,
 156         .fs_flags       = FS_USERNS_MOUNT,
 157 };
 158
 159 int __init sysfs_init(void)
 160 {
 161         int err = -ENOMEM;
 162
 163         sysfs_dir_cachep = kmem_cache_create("sysfs_dir_cache",
 164                                               sizeof(struct sysfs_dirent),
 165                                               0, 0, NULL);
 166         if (!sysfs_dir_cachep)
 167                 goto out;
 168
 169         err = sysfs_inode_init();
 170         if (err)
 171                 goto out_err;
 172
 173         err = register_filesystem(&sysfs_fs_type);
 174         if (!err) {
 175                 sysfs_mnt = kern_mount(&sysfs_fs_type);
 176                 if (IS_ERR(sysfs_mnt)) {
 177                         printk(KERN_ERR "sysfs: could not mount!\n");
 178                         err = PTR_ERR(sysfs_mnt);
 179                         sysfs_mnt = NULL;
 180                         unregister_filesystem(&sysfs_fs_type);
 181                         goto out_err;
 182                 }
 183         } else
 184                 goto out_err;
 185 out:
 186         return err;
 187 out_err:
 188         kmem_cache_destroy(sysfs_dir_cachep);
 189         sysfs_dir_cachep = NULL;
 190         goto out;
 191 }
 192
 193 #undef sysfs_get
 194 struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd)
 195 {
 196         return __sysfs_get(sd);
 197 }
 198 EXPORT_SYMBOL_GPL(sysfs_get);
 199
 200 #undef sysfs_put
 201 void sysfs_put(struct sysfs_dirent *sd)
 202 {
 203         __sysfs_put(sd);
 204 }
 205 EXPORT_SYMBOL_GPL(sysfs_put);