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 } 337