/* AFS dynamic root handling
 *
 * Copyright (C) 2018 Red Hat, Inc. All Rights Reserved.
 * Written by David Howells (dhowells@redhat.com)
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public Licence
 * as published by the Free Software Foundation; either version
 * 2 of the Licence, or (at your option) any later version.
 */

#include <linux/fs.h>
#include <linux/namei.h>
#include <linux/dns_resolver.h>
#include "internal.h"

const struct file_operations afs_dynroot_file_operations = {
        .open           = dcache_dir_open,
        .release        = dcache_dir_close,
        .iterate_shared = dcache_readdir,
        .llseek         = dcache_dir_lseek,
};

/*
 * Probe to see if a cell may exist.  This prevents positive dentries from
 * being created unnecessarily.
 */
static int afs_probe_cell_name(struct dentry *dentry)
{
        struct afs_cell *cell;
        const char *name = dentry->d_name.name;
        size_t len = dentry->d_name.len;
        int ret;

        /* Names prefixed with a dot are R/W mounts. */
        if (name[0] == '.') {
                if (len == 1)
                        return -EINVAL;
                name++;
                len--;
        }

        cell = afs_lookup_cell_rcu(afs_d2net(dentry), name, len);
        if (!IS_ERR(cell)) {
                afs_put_cell(afs_d2net(dentry), cell);
                return 0;
        }

        ret = dns_query("afsdb", name, len, "", NULL, NULL);
        if (ret == -ENODATA)
                ret = -EDESTADDRREQ;
        return ret;
}

/*
 * Try to auto mount the mountpoint with pseudo directory, if the autocell
 * operation is setted.
 */
struct inode *afs_try_auto_mntpt(struct dentry *dentry, struct inode *dir)
{
        struct afs_vnode *vnode = AFS_FS_I(dir);
        struct inode *inode;
        int ret = -ENOENT;

        _enter("%p{%pd}, {%x:%u}",
               dentry, dentry, vnode->fid.vid, vnode->fid.vnode);

        if (!test_bit(AFS_VNODE_AUTOCELL, &vnode->flags))
                goto out;

        ret = afs_probe_cell_name(dentry);
        if (ret < 0)
                goto out;

        inode = afs_iget_pseudo_dir(dir->i_sb, false);
        if (IS_ERR(inode)) {
                ret = PTR_ERR(inode);
                goto out;
        }

        _leave("= %p", inode);
        return inode;

out:
        _leave("= %d", ret);
        return ret == -ENOENT ? NULL : ERR_PTR(ret);
}

/*
 * Look up @cell in a dynroot directory.  This is a substitution for the
 * local cell name for the net namespace.
 */
static struct dentry *afs_lookup_atcell(struct dentry *dentry)
{
        struct afs_cell *cell;
        struct afs_net *net = afs_d2net(dentry);
        struct dentry *ret;
        unsigned int seq = 0;
        char *name;
        int len;

        if (!net->ws_cell)
                return ERR_PTR(-ENOENT);

        ret = ERR_PTR(-ENOMEM);
        name = kmalloc(AFS_MAXCELLNAME + 1, GFP_KERNEL);
        if (!name)
                goto out_p;

        rcu_read_lock();
        do {
                read_seqbegin_or_lock(&net->cells_lock, &seq);
                cell = rcu_dereference_raw(net->ws_cell);
                if (cell) {
                        len = cell->name_len;
                        memcpy(name, cell->name, len + 1);
                }
        } while (need_seqretry(&net->cells_lock, seq));
        done_seqretry(&net->cells_lock, seq);
        rcu_read_unlock();

        ret = ERR_PTR(-ENOENT);
        if (!cell)
                goto out_n;

        ret = lookup_one_len(name, dentry->d_parent, len);

        /* We don't want to d_add() the @cell dentry here as we don't want to
         * the cached dentry to hide changes to the local cell name.
         */

out_n:
        kfree(name);
out_p:
        return ret;
}

/*
 * Look up an entry in a dynroot directory.
 */
static struct dentry *afs_dynroot_lookup(struct inode *dir, struct dentry *dentry,
                                         unsigned int flags)
{
        _enter("%pd", dentry);

        ASSERTCMP(d_inode(dentry), ==, NULL);

        if (dentry->d_name.len >= AFSNAMEMAX) {
                _leave(" = -ENAMETOOLONG");
                return ERR_PTR(-ENAMETOOLONG);
        }

        if (dentry->d_name.len == 5 &&
            memcmp(dentry->d_name.name, "@cell", 5) == 0)
                return afs_lookup_atcell(dentry);

        return d_splice_alias(afs_try_auto_mntpt(dentry, dir), dentry);
}

const struct inode_operations afs_dynroot_inode_operations = {
        .lookup         = afs_dynroot_lookup,
};

/*
 * Dirs in the dynamic root don't need revalidation.
 */
static int afs_dynroot_d_revalidate(struct dentry *dentry, unsigned int flags)
{
        return 1;
}

/*
 * Allow the VFS to enquire as to whether a dentry should be unhashed (mustn't
 * sleep)
 * - called from dput() when d_count is going to 0.
 * - return 1 to request dentry be unhashed, 0 otherwise
 */
static int afs_dynroot_d_delete(const struct dentry *dentry)
{
        return d_really_is_positive(dentry);
}

const struct dentry_operations afs_dynroot_dentry_operations = {
        .d_revalidate   = afs_dynroot_d_revalidate,
        .d_delete       = afs_dynroot_d_delete,
        .d_release      = afs_d_release,
        .d_automount    = afs_d_automount,
};

/*
 * Create a manually added cell mount directory.
 * - The caller must hold net->proc_cells_lock
 */
int afs_dynroot_mkdir(struct afs_net *net, struct afs_cell *cell)
{
        struct super_block *sb = net->dynroot_sb;
        struct dentry *root, *subdir;
        int ret;

        if (!sb || atomic_read(&sb->s_active) == 0)
                return 0;

        /* Let the ->lookup op do the creation */
        root = sb->s_root;
        inode_lock(root->d_inode);
        subdir = lookup_one_len(cell->name, root, cell->name_len);
        if (IS_ERR(subdir)) {
                ret = PTR_ERR(subdir);
                goto unlock;
        }

        /* Note that we're retaining an extra ref on the dentry */
        subdir->d_fsdata = (void *)1UL;
        ret = 0;
unlock:
        inode_unlock(root->d_inode);
        return ret;
}

/*
 * Remove a manually added cell mount directory.
 * - The caller must hold net->proc_cells_lock
 */
void afs_dynroot_rmdir(struct afs_net *net, struct afs_cell *cell)
{
        struct super_block *sb = net->dynroot_sb;
        struct dentry *root, *subdir;

        if (!sb || atomic_read(&sb->s_active) == 0)
                return;

        root = sb->s_root;
        inode_lock(root->d_inode);

        /* Don't want to trigger a lookup call, which will re-add the cell */
        subdir = try_lookup_one_len(cell->name, root, cell->name_len);
        if (IS_ERR_OR_NULL(subdir)) {
                _debug("lookup %ld", PTR_ERR(subdir));
                goto no_dentry;
        }

        _debug("rmdir %pd %u", subdir, d_count(subdir));

        if (subdir->d_fsdata) {
                _debug("unpin %u", d_count(subdir));
                subdir->d_fsdata = NULL;
                dput(subdir);
        }
        dput(subdir);
no_dentry:
        inode_unlock(root->d_inode);
        _leave("");
}

/*
 * Populate a newly created dynamic root with cell names.
 */
int afs_dynroot_populate(struct super_block *sb)
{
        struct afs_cell *cell;
        struct afs_net *net = afs_sb2net(sb);
        int ret;

        if (mutex_lock_interruptible(&net->proc_cells_lock) < 0)
                return -ERESTARTSYS;

        net->dynroot_sb = sb;
        hlist_for_each_entry(cell, &net->proc_cells, proc_link) {
                ret = afs_dynroot_mkdir(net, cell);
                if (ret < 0)
                        goto error;
        }

        ret = 0;
out:
        mutex_unlock(&net->proc_cells_lock);
        return ret;

error:
        net->dynroot_sb = NULL;
        goto out;
}

/*
 * When a dynamic root that's in the process of being destroyed, depopulate it
 * of pinned directories.
 */
void afs_dynroot_depopulate(struct super_block *sb)
{
        struct afs_net *net = afs_sb2net(sb);
        struct dentry *root = sb->s_root, *subdir, *tmp;

        /* Prevent more subdirs from being created */
        mutex_lock(&net->proc_cells_lock);
        if (net->dynroot_sb == sb)
                net->dynroot_sb = NULL;
        mutex_unlock(&net->proc_cells_lock);

        inode_lock(root->d_inode);

        /* Remove all the pins for dirs created for manually added cells */
        list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
                if (subdir->d_fsdata) {
                        subdir->d_fsdata = NULL;
                        dput(subdir);
                }
        }

        inode_unlock(root->d_inode);
}