/*
 * 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>
 *
 * This file is released under the GPLv2.
 */

#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;

static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
{
        struct kernfs_root *root = kernfs_info(sb)->root;
        struct kernfs_syscall_ops *scops = root->syscall_ops;

        if (scops && scops->remount_fs)
                return scops->remount_fs(root, flags, data);
        return 0;
}

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,

        .remount_fs     = kernfs_sop_remount_fs,
        .show_options   = kernfs_sop_show_options,
        .show_path      = kernfs_sop_show_path,
};

/*
 * Similar to kernfs_fh_get_inode, this one gets kernfs node from inode
 * number and generation
 */
struct kernfs_node *kernfs_get_node_by_id(struct kernfs_root *root,
        const union kernfs_node_id *id)
{
        struct kernfs_node *kn;

        kn = kernfs_find_and_get_node_by_ino(root, id->ino);
        if (!kn)
                return NULL;
        if (kn->id.generation != id->generation) {
                kernfs_put(kn);
                return NULL;
        }
        return kn;
}

static struct inode *kernfs_fh_get_inode(struct super_block *sb,
                u64 ino, u32 generation)
{
        struct kernfs_super_info *info = kernfs_info(sb);
        struct inode *inode;
        struct kernfs_node *kn;

        if (ino == 0)
                return ERR_PTR(-ESTALE);

        kn = kernfs_find_and_get_node_by_ino(info->root, ino);
        if (!kn)
                return ERR_PTR(-ESTALE);
        inode = kernfs_get_inode(sb, kn);
        kernfs_put(kn);
        if (!inode)
                return ERR_PTR(-ESTALE);

        if (generation && inode->i_generation != generation) {
                /* we didn't find the right inode.. */
                iput(inode);
                return ERR_PTR(-ESTALE);
        }
        return inode;
}

static struct dentry *kernfs_fh_to_dentry(struct super_block *sb, struct fid *fid,
                int fh_len, int fh_type)
{
        return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
                                    kernfs_fh_get_inode);
}

static struct dentry *kernfs_fh_to_parent(struct super_block *sb, struct fid *fid,
                int fh_len, int fh_type)
{
        return generic_fh_to_parent(sb, fid, fh_len, fh_type,
                                    kernfs_fh_get_inode);
}

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 = {
        .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))
                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))
                        return ERR_PTR(-EINVAL);
                dtmp = lookup_one_len_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, unsigned long magic)
{
        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 = 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;

        /* 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, void *data)
{
        struct kernfs_super_info *sb_info = kernfs_info(sb);
        struct kernfs_super_info *info = data;

        return sb_info->root == info->root && sb_info->ns == info->ns;
}

static int kernfs_set_super(struct super_block *sb, void *data)
{
        int error;
        error = set_anon_super(sb, data);
        if (!error)
                sb->s_fs_info = data;
        return error;
}

/**
 * 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_mount_ns - kernfs mount helper
 * @fs_type: file_system_type of the fs being mounted
 * @flags: mount flags specified for the mount
 * @root: kernfs_root of the hierarchy being mounted
 * @magic: file system specific magic number
 * @new_sb_created: tell the caller if we allocated a new superblock
 * @ns: optional namespace tag of the mount
 *
 * This is to be called from each kernfs user's file_system_type->mount()
 * implementation, which should pass through the specified @fs_type and
 * @flags, and specify the hierarchy and namespace tag to mount via @root
 * and @ns, respectively.
 *
 * The return value can be passed to the vfs layer verbatim.
 */
struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
                                struct kernfs_root *root, unsigned long magic,
                                bool *new_sb_created, const void *ns)
{
        struct super_block *sb;
        struct kernfs_super_info *info;
        int error;

        info = kzalloc(sizeof(*info), GFP_KERNEL);
        if (!info)
                return ERR_PTR(-ENOMEM);

        info->root = root;
        info->ns = ns;

        sb = sget_userns(fs_type, kernfs_test_super, kernfs_set_super, flags,
                         &init_user_ns, info);
        if (IS_ERR(sb) || sb->s_fs_info != info)
                kfree(info);
        if (IS_ERR(sb))
                return ERR_CAST(sb);

        if (new_sb_created)
                *new_sb_created = !sb->s_root;

        if (!sb->s_root) {
                struct kernfs_super_info *info = kernfs_info(sb);

                error = kernfs_fill_super(sb, magic);
                if (error) {
                        deactivate_locked_super(sb);
                        return ERR_PTR(error);
                }
                sb->s_flags |= SB_ACTIVE;

                mutex_lock(&kernfs_mutex);
                list_add(&info->node, &root->supers);
                mutex_unlock(&kernfs_mutex);
        }

        return dget(sb->s_root);
}

/**
 * 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);
}

/**
 * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
 * @kernfs_root: the kernfs_root in question
 * @ns: the namespace tag
 *
 * Pin the superblock so the superblock won't be destroyed in subsequent
 * operations.  This can be used to block ->kill_sb() which may be useful
 * for kernfs users which dynamically manage superblocks.
 *
 * Returns NULL if there's no superblock associated to this kernfs_root, or
 * -EINVAL if the superblock is being freed.
 */
struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
{
        struct kernfs_super_info *info;
        struct super_block *sb = NULL;

        mutex_lock(&kernfs_mutex);
        list_for_each_entry(info, &root->supers, node) {
                if (info->ns == ns) {
                        sb = info->sb;
                        if (!atomic_inc_not_zero(&info->sb->s_active))
                                sb = ERR_PTR(-EINVAL);
                        break;
                }
        }
        mutex_unlock(&kernfs_mutex);
        return sb;
}

void __init kernfs_init(void)
{

        /*
         * the slab is freed in RCU context, so kernfs_find_and_get_node_by_ino
         * can access the slab lock free. This could introduce stale nodes,
         * please see how kernfs_find_and_get_node_by_ino filters out stale
         * nodes.
         */
        kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
                                              sizeof(struct kernfs_node),
                                              0,
                                              SLAB_PANIC | SLAB_TYPESAFE_BY_RCU,
                                              NULL);
}