fs/kernfs/mount.c

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This source file includes following definitions.
kernfs_sop_show_options
kernfs_sop_show_path
kernfs_get_node_by_id
kernfs_fh_get_inode
kernfs_fh_to_dentry
kernfs_fh_to_parent
kernfs_get_parent_dentry
kernfs_root_from_sb
find_next_ancestor
kernfs_node_dentry
kernfs_fill_super
kernfs_test_super
kernfs_set_super
kernfs_super_ns
kernfs_get_tree
kernfs_free_fs_context
kernfs_kill_sb
kernfs_init
   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * fs/kernfs/mount.c - kernfs mount implementation
   4  *
   5  * Copyright (c) 2001-3 Patrick Mochel
   6  * Copyright (c) 2007 SUSE Linux Products GmbH
   7  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   8  */
   9 
  10 #include <linux/fs.h>
  11 #include <linux/mount.h>
  12 #include <linux/init.h>
  13 #include <linux/magic.h>
  14 #include <linux/slab.h>
  15 #include <linux/pagemap.h>
  16 #include <linux/namei.h>
  17 #include <linux/seq_file.h>
  18 #include <linux/exportfs.h>
  19 
  20 #include "kernfs-internal.h"
  21 
  22 struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;
  23 
  24 static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
  25 {
  26         struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
  27         struct kernfs_syscall_ops *scops = root->syscall_ops;
  28 
  29         if (scops && scops->show_options)
  30                 return scops->show_options(sf, root);
  31         return 0;
  32 }
  33 
  34 static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
  35 {
  36         struct kernfs_node *node = kernfs_dentry_node(dentry);
  37         struct kernfs_root *root = kernfs_root(node);
  38         struct kernfs_syscall_ops *scops = root->syscall_ops;
  39 
  40         if (scops && scops->show_path)
  41                 return scops->show_path(sf, node, root);
  42 
  43         seq_dentry(sf, dentry, " \t\n\\");
  44         return 0;
  45 }
  46 
  47 const struct super_operations kernfs_sops = {
  48         .statfs         = simple_statfs,
  49         .drop_inode     = generic_delete_inode,
  50         .evict_inode    = kernfs_evict_inode,
  51 
  52         .show_options   = kernfs_sop_show_options,
  53         .show_path      = kernfs_sop_show_path,
  54 };
  55 
  56 /*
  57  * Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
  58  * number and generation
  59  */
  60 struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root,
  61         const union kernfs_node_id *id)
  62 {
  63         struct kernfs_node *kn;
  64 
  65         kn = kernfs_find_and_get_node_by_ino(root, id->ino);
  66         if (!kn)
  67                 return NULL;
  68         if (kn->id.generation != id->generation) {
  69                 kernfs_put(kn);
  70                 return NULL;
  71         }
  72         return kn;
  73 }
  74 
  75 static struct inode *kernfs_fh_get_inode(struct super_block *sb,
  76                 u64 ino, u32 generation)
  77 {
  78         struct kernfs_super_info *info = kernfs_info(sb);
  79         struct inode *inode;
  80         struct kernfs_node *kn;
  81 
  82         if (ino == 0)
  83                 return ERR_PTR(-ESTALE);
  84 
  85         kn = kernfs_find_and_get_node_by_ino(info->root, ino);
  86         if (!kn)
  87                 return ERR_PTR(-ESTALE);
  88         inode = kernfs_get_inode(sb, kn);
  89         kernfs_put(kn);
  90         if (!inode)
  91                 return ERR_PTR(-ESTALE);
  92 
  93         if (generation && inode->i_generation != generation) {
  94                 /* we didn't find the right inode.. */
  95                 iput(inode);
  96                 return ERR_PTR(-ESTALE);
  97         }
  98         return inode;
  99 }
 100 
 101 static struct dentry *kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid,
 102                 int fh_len, int fh_type)
 103 {
 104         return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
 105                                     kernfs_fh_get_inode);
 106 }
 107 
 108 static struct dentry *kernfs_fh_to_parent(struct super_block *sb, struct fid *fid,
 109                 int fh_len, int fh_type)
 110 {
 111         return generic_fh_to_parent(sb, fid, fh_len, fh_type,
 112                                     kernfs_fh_get_inode);
 113 }
 114 
 115 static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
 116 {
 117         struct kernfs_node *kn = kernfs_dentry_node(child);
 118 
 119         return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
 120 }
 121 
 122 static const struct export_operations kernfs_export_ops = {
 123         .fh_to_dentry   = kernfs_fh_to_dentry,
 124         .fh_to_parent   = kernfs_fh_to_parent,
 125         .get_parent     = kernfs_get_parent_dentry,
 126 };
 127 
 128 /**
 129  * kernfs_root_from_sb - determine kernfs_root associated with a super_block
 130  * @sb: the super_block in question
 131  *
 132  * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
 133  * %NULL is returned.
 134  */
 135 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
 136 {
 137         if (sb->s_op == &kernfs_sops)
 138                 return kernfs_info(sb)->root;
 139         return NULL;
 140 }
 141 
 142 /*
 143  * find the next ancestor in the path down to @child, where @parent was the
 144  * ancestor whose descendant we want to find.
 145  *
 146  * Say the path is /a/b/c/d.  @child is d, @parent is NULL.  We return the root
 147  * node.  If @parent is b, then we return the node for c.
 148  * Passing in d as @parent is not ok.
 149  */
 150 static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
 151                                               struct kernfs_node *parent)
 152 {
 153         if (child == parent) {
 154                 pr_crit_once("BUG in find_next_ancestor: called with parent == child");
 155                 return NULL;
 156         }
 157 
 158         while (child->parent != parent) {
 159                 if (!child->parent)
 160                         return NULL;
 161                 child = child->parent;
 162         }
 163 
 164         return child;
 165 }
 166 
 167 /**
 168  * kernfs_node_dentry - get a dentry for the given kernfs_node
 169  * @kn: kernfs_node for which a dentry is needed
 170  * @sb: the kernfs super_block
 171  */
 172 struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
 173                                   struct super_block *sb)
 174 {
 175         struct dentry *dentry;
 176         struct kernfs_node *knparent = NULL;
 177 
 178         BUG_ON(sb->s_op != &kernfs_sops);
 179 
 180         dentry = dget(sb->s_root);
 181 
 182         /* Check if this is the root kernfs_node */
 183         if (!kn->parent)
 184                 return dentry;
 185 
 186         knparent = find_next_ancestor(kn, NULL);
 187         if (WARN_ON(!knparent)) {
 188                 dput(dentry);
 189                 return ERR_PTR(-EINVAL);
 190         }
 191 
 192         do {
 193                 struct dentry *dtmp;
 194                 struct kernfs_node *kntmp;
 195 
 196                 if (kn == knparent)
 197                         return dentry;
 198                 kntmp = find_next_ancestor(kn, knparent);
 199                 if (WARN_ON(!kntmp)) {
 200                         dput(dentry);
 201                         return ERR_PTR(-EINVAL);
 202                 }
 203                 dtmp = lookup_one_len_unlocked(kntmp->name, dentry,
 204                                                strlen(kntmp->name));
 205                 dput(dentry);
 206                 if (IS_ERR(dtmp))
 207                         return dtmp;
 208                 knparent = kntmp;
 209                 dentry = dtmp;
 210         } while (true);
 211 }
 212 
 213 static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
 214 {
 215         struct kernfs_super_info *info = kernfs_info(sb);
 216         struct inode *inode;
 217         struct dentry *root;
 218 
 219         info->sb = sb;
 220         /* Userspace would break if executables or devices appear on sysfs */
 221         sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
 222         sb->s_blocksize = PAGE_SIZE;
 223         sb->s_blocksize_bits = PAGE_SHIFT;
 224         sb->s_magic = kfc->magic;
 225         sb->s_op = &kernfs_sops;
 226         sb->s_xattr = kernfs_xattr_handlers;
 227         if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
 228                 sb->s_export_op = &kernfs_export_ops;
 229         sb->s_time_gran = 1;
 230 
 231         /* sysfs dentries and inodes don't require IO to create */
 232         sb->s_shrink.seeks = 0;
 233 
 234         /* get root inode, initialize and unlock it */
 235         mutex_lock(&kernfs_mutex);
 236         inode = kernfs_get_inode(sb, info->root->kn);
 237         mutex_unlock(&kernfs_mutex);
 238         if (!inode) {
 239                 pr_debug("kernfs: could not get root inode\n");
 240                 return -ENOMEM;
 241         }
 242 
 243         /* instantiate and link root dentry */
 244         root = d_make_root(inode);
 245         if (!root) {
 246                 pr_debug("%s: could not get root dentry!\n", __func__);
 247                 return -ENOMEM;
 248         }
 249         sb->s_root = root;
 250         sb->s_d_op = &kernfs_dops;
 251         return 0;
 252 }
 253 
 254 static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
 255 {
 256         struct kernfs_super_info *sb_info = kernfs_info(sb);
 257         struct kernfs_super_info *info = fc->s_fs_info;
 258 
 259         return sb_info->root == info->root && sb_info->ns == info->ns;
 260 }
 261 
 262 static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
 263 {
 264         struct kernfs_fs_context *kfc = fc->fs_private;
 265 
 266         kfc->ns_tag = NULL;
 267         return set_anon_super_fc(sb, fc);
 268 }
 269 
 270 /**
 271  * kernfs_super_ns - determine the namespace tag of a kernfs super_block
 272  * @sb: super_block of interest
 273  *
 274  * Return the namespace tag associated with kernfs super_block @sb.
 275  */
 276 const void *kernfs_super_ns(struct super_block *sb)
 277 {
 278         struct kernfs_super_info *info = kernfs_info(sb);
 279 
 280         return info->ns;
 281 }
 282 
 283 /**
 284  * kernfs_get_tree - kernfs filesystem access/retrieval helper
 285  * @fc: The filesystem context.
 286  *
 287  * This is to be called from each kernfs user's fs_context->ops->get_tree()
 288  * implementation, which should set the specified ->@fs_type and ->@flags, and
 289  * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
 290  * respectively.
 291  */
 292 int kernfs_get_tree(struct fs_context *fc)
 293 {
 294         struct kernfs_fs_context *kfc = fc->fs_private;
 295         struct super_block *sb;
 296         struct kernfs_super_info *info;
 297         int error;
 298 
 299         info = kzalloc(sizeof(*info), GFP_KERNEL);
 300         if (!info)
 301                 return -ENOMEM;
 302 
 303         info->root = kfc->root;
 304         info->ns = kfc->ns_tag;
 305         INIT_LIST_HEAD(&info->node);
 306 
 307         fc->s_fs_info = info;
 308         sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
 309         if (IS_ERR(sb))
 310                 return PTR_ERR(sb);
 311 
 312         if (!sb->s_root) {
 313                 struct kernfs_super_info *info = kernfs_info(sb);
 314 
 315                 kfc->new_sb_created = true;
 316 
 317                 error = kernfs_fill_super(sb, kfc);
 318                 if (error) {
 319                         deactivate_locked_super(sb);
 320                         return error;
 321                 }
 322                 sb->s_flags |= SB_ACTIVE;
 323 
 324                 mutex_lock(&kernfs_mutex);
 325                 list_add(&info->node, &info->root->supers);
 326                 mutex_unlock(&kernfs_mutex);
 327         }
 328 
 329         fc->root = dget(sb->s_root);
 330         return 0;
 331 }
 332 
 333 void kernfs_free_fs_context(struct fs_context *fc)
 334 {
 335         /* Note that we don't deal with kfc->ns_tag here. */
 336         kfree(fc->s_fs_info);
 337         fc->s_fs_info = NULL;
 338 }
 339 
 340 /**
 341  * kernfs_kill_sb - kill_sb for kernfs
 342  * @sb: super_block being killed
 343  *
 344  * This can be used directly for file_system_type->kill_sb().  If a kernfs
 345  * user needs extra cleanup, it can implement its own kill_sb() and call
 346  * this function at the end.
 347  */
 348 void kernfs_kill_sb(struct super_block *sb)
 349 {
 350         struct kernfs_super_info *info = kernfs_info(sb);
 351 
 352         mutex_lock(&kernfs_mutex);
 353         list_del(&info->node);
 354         mutex_unlock(&kernfs_mutex);
 355 
 356         /*
 357          * Remove the superblock from fs_supers/s_instances
 358          * so we can't find it, before freeing kernfs_super_info.
 359          */
 360         kill_anon_super(sb);
 361         kfree(info);
 362 }
 363 
 364 void __init kernfs_init(void)
 365 {
 366 
 367         /*
 368          * the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
 369          * can access the slab lock free. This could introduce stale nodes,
 370          * please see how kernfs_find_and_get_node_by_ino filters out stale
 371          * nodes.
 372          */
 373         kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
 374                                               sizeof(struct kernfs_node),
 375                                               0,
 376                                               SLAB_PANIC | SLAB_TYPESAFE_BY_RCU,
 377                                               NULL);
 378 
 379         /* Creates slab cache for kernfs inode attributes */
 380         kernfs_iattrs_cache  = kmem_cache_create("kernfs_iattrs_cache",
 381                                               sizeof(struct kernfs_iattrs),
 382                                               0, SLAB_PANIC, NULL);
 383 }
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root/fs/kernfs/mount.c

DEFINITIONS
