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