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