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- // SPDX-License-Identifier: GPL-2.0-only
- /*
- * fs/kernfs/mount.c - kernfs mount implementation
- *
- * Copyright (c) 2001-3 Patrick Mochel
- * Copyright (c) 2007 SUSE Linux Products GmbH
- * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
- */
- #include <linux/fs.h>
- #include <linux/mount.h>
- #include <linux/init.h>
- #include <linux/magic.h>
- #include <linux/slab.h>
- #include <linux/pagemap.h>
- #include <linux/namei.h>
- #include <linux/seq_file.h>
- #include <linux/exportfs.h>
- #include "kernfs-internal.h"
- struct kmem_cache *kernfs_node_cache, *kernfs_iattrs_cache;
- static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
- {
- struct kernfs_root *root = kernfs_root(kernfs_dentry_node(dentry));
- struct kernfs_syscall_ops *scops = root->syscall_ops;
- if (scops && scops->show_options)
- return scops->show_options(sf, root);
- return 0;
- }
- static int kernfs_sop_show_path(struct seq_file *sf, struct dentry *dentry)
- {
- struct kernfs_node *node = kernfs_dentry_node(dentry);
- struct kernfs_root *root = kernfs_root(node);
- struct kernfs_syscall_ops *scops = root->syscall_ops;
- if (scops && scops->show_path)
- return scops->show_path(sf, node, root);
- seq_dentry(sf, dentry, " \t\n\\");
- return 0;
- }
- const struct super_operations kernfs_sops = {
- .statfs = simple_statfs,
- .drop_inode = generic_delete_inode,
- .evict_inode = kernfs_evict_inode,
- .show_options = kernfs_sop_show_options,
- .show_path = kernfs_sop_show_path,
- };
- static int kernfs_encode_fh(struct inode *inode, __u32 *fh, int *max_len,
- struct inode *parent)
- {
- struct kernfs_node *kn = inode->i_private;
- if (*max_len < 2) {
- *max_len = 2;
- return FILEID_INVALID;
- }
- *max_len = 2;
- *(u64 *)fh = kn->id;
- return FILEID_KERNFS;
- }
- static struct dentry *__kernfs_fh_to_dentry(struct super_block *sb,
- struct fid *fid, int fh_len,
- int fh_type, bool get_parent)
- {
- struct kernfs_super_info *info = kernfs_info(sb);
- struct kernfs_node *kn;
- struct inode *inode;
- u64 id;
- if (fh_len < 2)
- return NULL;
- switch (fh_type) {
- case FILEID_KERNFS:
- id = *(u64 *)fid;
- break;
- case FILEID_INO32_GEN:
- case FILEID_INO32_GEN_PARENT:
- /*
- * blk_log_action() exposes "LOW32,HIGH32" pair without
- * type and userland can call us with generic fid
- * constructed from them. Combine it back to ID. See
- * blk_log_action().
- */
- id = ((u64)fid->i32.gen << 32) | fid->i32.ino;
- break;
- default:
- return NULL;
- }
- kn = kernfs_find_and_get_node_by_id(info->root, id);
- if (!kn)
- return ERR_PTR(-ESTALE);
- if (get_parent) {
- struct kernfs_node *parent;
- parent = kernfs_get_parent(kn);
- kernfs_put(kn);
- kn = parent;
- if (!kn)
- return ERR_PTR(-ESTALE);
- }
- inode = kernfs_get_inode(sb, kn);
- kernfs_put(kn);
- if (!inode)
- return ERR_PTR(-ESTALE);
- return d_obtain_alias(inode);
- }
- static struct dentry *kernfs_fh_to_dentry(struct super_block *sb,
- struct fid *fid, int fh_len,
- int fh_type)
- {
- return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, false);
- }
- static struct dentry *kernfs_fh_to_parent(struct super_block *sb,
- struct fid *fid, int fh_len,
- int fh_type)
- {
- return __kernfs_fh_to_dentry(sb, fid, fh_len, fh_type, true);
- }
- static struct dentry *kernfs_get_parent_dentry(struct dentry *child)
- {
- struct kernfs_node *kn = kernfs_dentry_node(child);
- return d_obtain_alias(kernfs_get_inode(child->d_sb, kn->parent));
- }
- static const struct export_operations kernfs_export_ops = {
- .encode_fh = kernfs_encode_fh,
- .fh_to_dentry = kernfs_fh_to_dentry,
- .fh_to_parent = kernfs_fh_to_parent,
- .get_parent = kernfs_get_parent_dentry,
- };
- /**
- * kernfs_root_from_sb - determine kernfs_root associated with a super_block
- * @sb: the super_block in question
- *
- * Return the kernfs_root associated with @sb. If @sb is not a kernfs one,
- * %NULL is returned.
- */
- struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
- {
- if (sb->s_op == &kernfs_sops)
- return kernfs_info(sb)->root;
- return NULL;
- }
- /*
- * find the next ancestor in the path down to @child, where @parent was the
- * ancestor whose descendant we want to find.
- *
- * Say the path is /a/b/c/d. @child is d, @parent is NULL. We return the root
- * node. If @parent is b, then we return the node for c.
- * Passing in d as @parent is not ok.
- */
- static struct kernfs_node *find_next_ancestor(struct kernfs_node *child,
- struct kernfs_node *parent)
- {
- if (child == parent) {
- pr_crit_once("BUG in find_next_ancestor: called with parent == child");
- return NULL;
- }
- while (child->parent != parent) {
- if (!child->parent)
- return NULL;
- child = child->parent;
- }
- return child;
- }
- /**
- * kernfs_node_dentry - get a dentry for the given kernfs_node
- * @kn: kernfs_node for which a dentry is needed
- * @sb: the kernfs super_block
- */
- struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
- struct super_block *sb)
- {
- struct dentry *dentry;
- struct kernfs_node *knparent = NULL;
- BUG_ON(sb->s_op != &kernfs_sops);
- dentry = dget(sb->s_root);
- /* Check if this is the root kernfs_node */
- if (!kn->parent)
- return dentry;
- knparent = find_next_ancestor(kn, NULL);
- if (WARN_ON(!knparent)) {
- dput(dentry);
- return ERR_PTR(-EINVAL);
- }
- do {
- struct dentry *dtmp;
- struct kernfs_node *kntmp;
- if (kn == knparent)
- return dentry;
- kntmp = find_next_ancestor(kn, knparent);
- if (WARN_ON(!kntmp)) {
- dput(dentry);
- return ERR_PTR(-EINVAL);
- }
- dtmp = lookup_positive_unlocked(kntmp->name, dentry,
- strlen(kntmp->name));
- dput(dentry);
- if (IS_ERR(dtmp))
- return dtmp;
- knparent = kntmp;
- dentry = dtmp;
- } while (true);
- }
- static int kernfs_fill_super(struct super_block *sb, struct kernfs_fs_context *kfc)
- {
- struct kernfs_super_info *info = kernfs_info(sb);
- struct inode *inode;
- struct dentry *root;
- info->sb = sb;
- /* Userspace would break if executables or devices appear on sysfs */
- sb->s_iflags |= SB_I_NOEXEC | SB_I_NODEV;
- sb->s_blocksize = PAGE_SIZE;
- sb->s_blocksize_bits = PAGE_SHIFT;
- sb->s_magic = kfc->magic;
- sb->s_op = &kernfs_sops;
- sb->s_xattr = kernfs_xattr_handlers;
- if (info->root->flags & KERNFS_ROOT_SUPPORT_EXPORTOP)
- sb->s_export_op = &kernfs_export_ops;
- sb->s_time_gran = 1;
- /* sysfs dentries and inodes don't require IO to create */
- sb->s_shrink.seeks = 0;
- /* get root inode, initialize and unlock it */
- mutex_lock(&kernfs_mutex);
- inode = kernfs_get_inode(sb, info->root->kn);
- mutex_unlock(&kernfs_mutex);
- if (!inode) {
- pr_debug("kernfs: could not get root inode\n");
- return -ENOMEM;
- }
- /* instantiate and link root dentry */
- root = d_make_root(inode);
- if (!root) {
- pr_debug("%s: could not get root dentry!\n", __func__);
- return -ENOMEM;
- }
- sb->s_root = root;
- sb->s_d_op = &kernfs_dops;
- return 0;
- }
- static int kernfs_test_super(struct super_block *sb, struct fs_context *fc)
- {
- struct kernfs_super_info *sb_info = kernfs_info(sb);
- struct kernfs_super_info *info = fc->s_fs_info;
- return sb_info->root == info->root && sb_info->ns == info->ns;
- }
- static int kernfs_set_super(struct super_block *sb, struct fs_context *fc)
- {
- struct kernfs_fs_context *kfc = fc->fs_private;
- kfc->ns_tag = NULL;
- return set_anon_super_fc(sb, fc);
- }
- /**
- * kernfs_super_ns - determine the namespace tag of a kernfs super_block
- * @sb: super_block of interest
- *
- * Return the namespace tag associated with kernfs super_block @sb.
- */
- const void *kernfs_super_ns(struct super_block *sb)
- {
- struct kernfs_super_info *info = kernfs_info(sb);
- return info->ns;
- }
- /**
- * kernfs_get_tree - kernfs filesystem access/retrieval helper
- * @fc: The filesystem context.
- *
- * This is to be called from each kernfs user's fs_context->ops->get_tree()
- * implementation, which should set the specified ->@fs_type and ->@flags, and
- * specify the hierarchy and namespace tag to mount via ->@root and ->@ns,
- * respectively.
- */
- int kernfs_get_tree(struct fs_context *fc)
- {
- struct kernfs_fs_context *kfc = fc->fs_private;
- struct super_block *sb;
- struct kernfs_super_info *info;
- int error;
- info = kzalloc(sizeof(*info), GFP_KERNEL);
- if (!info)
- return -ENOMEM;
- info->root = kfc->root;
- info->ns = kfc->ns_tag;
- INIT_LIST_HEAD(&info->node);
- fc->s_fs_info = info;
- sb = sget_fc(fc, kernfs_test_super, kernfs_set_super);
- if (IS_ERR(sb))
- return PTR_ERR(sb);
- if (!sb->s_root) {
- struct kernfs_super_info *info = kernfs_info(sb);
- kfc->new_sb_created = true;
- error = kernfs_fill_super(sb, kfc);
- if (error) {
- deactivate_locked_super(sb);
- return error;
- }
- sb->s_flags |= SB_ACTIVE;
- mutex_lock(&kernfs_mutex);
- list_add(&info->node, &info->root->supers);
- mutex_unlock(&kernfs_mutex);
- }
- fc->root = dget(sb->s_root);
- return 0;
- }
- void kernfs_free_fs_context(struct fs_context *fc)
- {
- /* Note that we don't deal with kfc->ns_tag here. */
- kfree(fc->s_fs_info);
- fc->s_fs_info = NULL;
- }
- /**
- * kernfs_kill_sb - kill_sb for kernfs
- * @sb: super_block being killed
- *
- * This can be used directly for file_system_type->kill_sb(). If a kernfs
- * user needs extra cleanup, it can implement its own kill_sb() and call
- * this function at the end.
- */
- void kernfs_kill_sb(struct super_block *sb)
- {
- struct kernfs_super_info *info = kernfs_info(sb);
- mutex_lock(&kernfs_mutex);
- list_del(&info->node);
- mutex_unlock(&kernfs_mutex);
- /*
- * Remove the superblock from fs_supers/s_instances
- * so we can't find it, before freeing kernfs_super_info.
- */
- kill_anon_super(sb);
- kfree(info);
- }
- void __init kernfs_init(void)
- {
- kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
- sizeof(struct kernfs_node),
- 0, SLAB_PANIC, NULL);
- /* Creates slab cache for kernfs inode attributes */
- kernfs_iattrs_cache = kmem_cache_create("kernfs_iattrs_cache",
- sizeof(struct kernfs_iattrs),
- 0, SLAB_PANIC, NULL);
- }
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