fs/kernfs/mount.c

   1 /*
   2  * fs/kernfs/mount.c - kernfs mount implementation
   3  *
   4  * Copyright (c) 2001-3 Patrick Mochel
   5  * Copyright (c) 2007 SUSE Linux Products GmbH
   6  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   7  *
   8  * This file is released under the GPLv2.
   9  */
  10
  11 #include <linux/fs.h>
  12 #include <linux/mount.h>
  13 #include <linux/init.h>
  14 #include <linux/magic.h>
  15 #include <linux/slab.h>
  16 #include <linux/pagemap.h>
  17 #include <linux/namei.h>
  18 #include <linux/seq_file.h>
  19
  20 #include "kernfs-internal.h"
  21
  22 struct kmem_cache *kernfs_node_cache;
  23
  24 static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
  25 {
  26         struct kernfs_root *root = kernfs_info(sb)->root;
  27         struct kernfs_syscall_ops *scops = root->syscall_ops;
  28
  29         if (scops && scops->remount_fs)
  30                 return scops->remount_fs(root, flags, data);
  31         return 0;
  32 }
  33
  34 static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
  35 {
  36         struct kernfs_root *root = kernfs_root(dentry->d_fsdata);
  37         struct kernfs_syscall_ops *scops = root->syscall_ops;
  38
  39         if (scops && scops->show_options)
  40                 return scops->show_options(sf, root);
  41         return 0;
  42 }
  43
  44 static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
  45 {
  46         struct kernfs_node *node = dentry->d_fsdata;
  47         struct kernfs_root *root = kernfs_root(node);
  48         struct kernfs_syscall_ops *scops = root->syscall_ops;
  49
  50         if (scops && scops->show_path)
  51                 return scops->show_path(sf, node, root);
  52
  53         seq_dentry(sf, dentry, " \t\n\\");
  54         return 0;
  55 }
  56
  57 const struct super_operations kernfs_sops = {
  58         .statfs         = simple_statfs,
  59         .drop_inode     = generic_delete_inode,
  60         .evict_inode    = kernfs_evict_inode,
  61
  62         .remount_fs     = kernfs_sop_remount_fs,
  63         .show_options   = kernfs_sop_show_options,
  64         .show_path      = kernfs_sop_show_path,
  65 };
  66
  67 /**
  68  * kernfs_root_from_sb - determine kernfs_root associated with a super_block
  69  * @sb: the super_block in question
  70  *
  71  * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
  72  * %NULL is returned.
  73  */
  74 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
  75 {
  76         if (sb->s_op == &kernfs_sops)
  77                 return kernfs_info(sb)->root;
  78         return NULL;
  79 }
  80
  81 /*
  82  * find the next ancestor in the path down to @child, where @parent was the
  83  * ancestor whose descendant we want to find.
  84  *
  85  * Say the path is /a/b/c/d.  @child is d, @parent is NULL.  We return the root
  86  * node.  If @parent is b, then we return the node for c.
  87  * Passing in d as @parent is not ok.
  88  */
  89 static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
  90                                               struct kernfs_node *parent)
  91 {
  92         if (child == parent) {
  93                 pr_crit_once("BUG in find_next_ancestor: called with parent == child");
  94                 return NULL;
  95         }
  96
  97         while (child->parent != parent) {
  98                 if (!child->parent)
  99                         return NULL;
 100                 child = child->parent;
 101         }
 102
 103         return child;
 104 }
 105
 106 /**
 107  * kernfs_node_dentry - get a dentry for the given kernfs_node
 108  * @kn: kernfs_node for which a dentry is needed
 109  * @sb: the kernfs super_block
 110  */
 111 struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 112                                   struct super_block *sb)
 113 {
 114         struct dentry *dentry;
 115         struct kernfs_node *knparent = NULL;
 116
 117         BUG_ON(sb->s_op != &kernfs_sops);
 118
 119         dentry = dget(sb->s_root);
 120
 121         /* Check if this is the root kernfs_node */
 122         if (!kn->parent)
 123                 return dentry;
 124
 125         knparent = find_next_ancestor(kn, NULL);
 126         if (WARN_ON(!knparent))
 127                 return ERR_PTR(-EINVAL);
 128
 129         do {
 130                 struct dentry *dtmp;
 131                 struct kernfs_node *kntmp;
 132
 133                 if (kn == knparent)
 134                         return dentry;
 135                 kntmp = find_next_ancestor(kn, knparent);
 136                 if (WARN_ON(!kntmp))
 137                         return ERR_PTR(-EINVAL);
 138                 dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
 139                                                strlen(kntmp->name));
 140                 dput(dentry);
 141                 if (IS_ERR(dtmp))
 142                         return dtmp;
 143                 knparent = kntmp;
 144                 dentry = dtmp;
 145         } while (true);
 146 }
 147
 148 static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
 149 {
 150         struct kernfs_super_info *info = kernfs_info(sb);
 151         struct inode *inode;
 152         struct dentry *root;
 153
 154         info->sb = sb;
 155         /* Userspace would break if executables or devices appear on sysfs */
 156         sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
 157         sb->s_blocksize = PAGE_SIZE;
 158         sb->s_blocksize_bits = PAGE_SHIFT;
 159         sb->s_magic = magic;
 160         sb->s_op = &kernfs_sops;
 161         sb->s_xattr = kernfs_xattr_handlers;
 162         sb->s_time_gran = 1;
 163
 164         /* get root inode, initialize and unlock it */
 165         mutex_lock(&kernfs_mutex);
 166         inode = kernfs_get_inode(sb, info->root->kn);
 167         mutex_unlock(&kernfs_mutex);
 168         if (!inode) {
 169                 pr_debug("kernfs: could not get root inode\n");
 170                 return -ENOMEM;
 171         }
 172
 173         /* instantiate and link root dentry */
 174         root = d_make_root(inode);
 175         if (!root) {
 176                 pr_debug("%s: could not get root dentry!\n", __func__);
 177                 return -ENOMEM;
 178         }
 179         kernfs_get(info->root->kn);
 180         root->d_fsdata = info->root->kn;
 181         sb->s_root = root;
 182         sb->s_d_op = &kernfs_dops;
 183         return 0;
 184 }
 185
 186 static int kernfs_test_super(struct super_block *sb, void *data)
 187 {
 188         struct kernfs_super_info *sb_info = kernfs_info(sb);
 189         struct kernfs_super_info *info = data;
 190
 191         return sb_info->root == info->root && sb_info->ns == info->ns;
 192 }
 193
 194 static int kernfs_set_super(struct super_block *sb, void *data)
 195 {
 196         int error;
 197         error = set_anon_super(sb, data);
 198         if (!error)
 199                 sb->s_fs_info = data;
 200         return error;
 201 }
 202
 203 /**
 204  * kernfs_super_ns - determine the namespace tag of a kernfs super_block
 205  * @sb: super_block of interest
 206  *
 207  * Return the namespace tag associated with kernfs super_block @sb.
 208  */
 209 const void *kernfs_super_ns(struct super_block *sb)
 210 {
 211         struct kernfs_super_info *info = kernfs_info(sb);
 212
 213         return info->ns;
 214 }
 215
 216 /**
 217  * kernfs_mount_ns - kernfs mount helper
 218  * @fs_type: file_system_type of the fs being mounted
 219  * @flags: mount flags specified for the mount
 220  * @root: kernfs_root of the hierarchy being mounted
 221  * @magic: file system specific magic number
 222  * @new_sb_created: tell the caller if we allocated a new superblock
 223  * @ns: optional namespace tag of the mount
 224  *
 225  * This is to be called from each kernfs user's file_system_type->mount()
 226  * implementation, which should pass through the specified @fs_type and
 227  * @flags, and specify the hierarchy and namespace tag to mount via @root
 228  * and @ns, respectively.
 229  *
 230  * The return value can be passed to the vfs layer verbatim.
 231  */
 232 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
 233                                 struct kernfs_root *root, unsigned long magic,
 234                                 bool *new_sb_created, const void *ns)
 235 {
 236         struct super_block *sb;
 237         struct kernfs_super_info *info;
 238         int error;
 239
 240         info = kzalloc(sizeof(*info), GFP_KERNEL);
 241         if (!info)
 242                 return ERR_PTR(-ENOMEM);
 243
 244         info->root = root;
 245         info->ns = ns;
 246
 247         sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
 248                          &init_user_ns, info);
 249         if (IS_ERR(sb) || sb->s_fs_info != info)
 250                 kfree(info);
 251         if (IS_ERR(sb))
 252                 return ERR_CAST(sb);
 253
 254         if (new_sb_created)
 255                 *new_sb_created = !sb->s_root;
 256
 257         if (!sb->s_root) {
 258                 struct kernfs_super_info *info = kernfs_info(sb);
 259
 260                 error = kernfs_fill_super(sb, magic);
 261                 if (error) {
 262                         deactivate_locked_super(sb);
 263                         return ERR_PTR(error);
 264                 }
 265                 sb->s_flags |= MS_ACTIVE;
 266
 267                 mutex_lock(&kernfs_mutex);
 268                 list_add(&info->node, &root->supers);
 269                 mutex_unlock(&kernfs_mutex);
 270         }
 271
 272         return dget(sb->s_root);
 273 }
 274
 275 /**
 276  * kernfs_kill_sb - kill_sb for kernfs
 277  * @sb: super_block being killed
 278  *
 279  * This can be used directly for file_system_type->kill_sb().  If a kernfs
 280  * user needs extra cleanup, it can implement its own kill_sb() and call
 281  * this function at the end.
 282  */
 283 void kernfs_kill_sb(struct super_block *sb)
 284 {
 285         struct kernfs_super_info *info = kernfs_info(sb);
 286         struct kernfs_node *root_kn = sb->s_root->d_fsdata;
 287
 288         mutex_lock(&kernfs_mutex);
 289         list_del(&info->node);
 290         mutex_unlock(&kernfs_mutex);
 291
 292         /*
 293          * Remove the superblock from fs_supers/s_instances
 294          * so we can't find it, before freeing kernfs_super_info.
 295          */
 296         kill_anon_super(sb);
 297         kfree(info);
 298         kernfs_put(root_kn);
 299 }
 300
 301 /**
 302  * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
 303  * @kernfs_root: the kernfs_root in question
 304  * @ns: the namespace tag
 305  *
 306  * Pin the superblock so the superblock won't be destroyed in subsequent
 307  * operations.  This can be used to block ->kill_sb() which may be useful
 308  * for kernfs users which dynamically manage superblocks.
 309  *
 310  * Returns NULL if there's no superblock associated to this kernfs_root, or
 311  * -EINVAL if the superblock is being freed.
 312  */
 313 struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
 314 {
 315         struct kernfs_super_info *info;
 316         struct super_block *sb = NULL;
 317
 318         mutex_lock(&kernfs_mutex);
 319         list_for_each_entry(info, &root->supers, node) {
 320                 if (info->ns == ns) {
 321                         sb = info->sb;
 322                         if (!atomic_inc_not_zero(&info->sb->s_active))
 323                                 sb = ERR_PTR(-EINVAL);
 324                         break;
 325                 }
 326         }
 327         mutex_unlock(&kernfs_mutex);
 328         return sb;
 329 }
 330
 331 void __init kernfs_init(void)
 332 {
 333         kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
 334                                               sizeof(struct kernfs_node),
 335                                               0, SLAB_PANIC, NULL);
 336 }