// 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 */
        down_read(&kernfs_rwsem);
        inode = kernfs_get_inode(sb, info->root->kn);
        up_read(&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.
 */
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;

                down_write(&kernfs_rwsem);
                list_add(&info->node, &info->root->supers);
                up_write(&kernfs_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);

        down_write(&kernfs_rwsem);
        list_del(&info->node);
        up_write(&kernfs_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);
}

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);
}