// 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 <[email protected]>
*/
#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 <linux/uuid.h>
#include <linux/statfs.h>
#include "kernfs-internal.h"
struct kmem_cache *kernfs_node_cache __ro_after_init;
struct kmem_cache *kernfs_iattrs_cache __ro_after_init;
struct kernfs_global_locks *kernfs_locks __ro_after_init;
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;
}
static int kernfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
simple_statfs(dentry, buf);
buf->f_fsid = uuid_to_fsid(dentry->d_sb->s_uuid.b);
return 0;
}
const struct super_operations kernfs_sops = {
.statfs = kernfs_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);
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
*
* Return: the dentry pointer
*/
struct dentry *kernfs_node_dentry(struct kernfs_node *kn,
struct super_block *sb)
{
struct dentry *dentry;
struct kernfs_node *knparent;
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 kernfs_root *kf_root = kfc->root;
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 */
down_read(&kf_root->kernfs_rwsem);
inode = kernfs_get_inode(sb, info->root->kn);
up_read(&kf_root->kernfs_rwsem);
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.
*
* Return: %0 on success, -errno on failure.
*/
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);
struct kernfs_root *root = kfc->root;
kfc->new_sb_created = true;
error = kernfs_fill_super(sb, kfc);
if (error) {
deactivate_locked_super(sb);
return error;
}
sb->s_flags |= SB_ACTIVE;
uuid_t uuid;
uuid_gen(&uuid);
super_set_uuid(sb, uuid.b, sizeof(uuid));
down_write(&root->kernfs_supers_rwsem);
list_add(&info->node, &info->root->supers);
up_write(&root->kernfs_supers_rwsem);
}
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);
struct kernfs_root *root = info->root;
down_write(&root->kernfs_supers_rwsem);
list_del(&info->node);
up_write(&root->kernfs_supers_rwsem);
/*
* 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);
}
static void __init kernfs_mutex_init(void)
{
int count;
for (count = 0; count < NR_KERNFS_LOCKS; count++)
mutex_init(&kernfs_locks->open_file_mutex[count]);
}
static void __init kernfs_lock_init(void)
{
kernfs_locks = kmalloc(sizeof(struct kernfs_global_locks), GFP_KERNEL);
WARN_ON(!kernfs_locks);
kernfs_mutex_init();
}
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);
kernfs_lock_init();
}
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