/*
 * Copyright (c) 1998-2014 Erez Zadok
 * Copyright (c) 2009	   Shrikar Archak
 * Copyright (c) 2003-2014 Stony Brook University
 * Copyright (c) 2003-2014 The Research Foundation of SUNY
 * Copyright (C) 2013-2014 Motorola Mobility, LLC
 * Copyright (C) 2017      Google, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/ctype.h>
#include "esdfs.h"

/*
 * returns: -ERRNO if error (returned to user)
 *          0: tell VFS to invalidate dentry
 *          1: dentry is valid
 */
static int esdfs_d_revalidate(struct dentry *dentry, unsigned int flags)
{
	struct path lower_path;
	struct path lower_parent_path;
	struct dentry *parent_dentry = NULL;
	struct dentry *lower_dentry = NULL;
	struct dentry *lower_parent_dentry = NULL;
	int err = 1;

	if (flags & LOOKUP_RCU)
		return -ECHILD;

	/* short-circuit if it's root */
	spin_lock(&dentry->d_lock);
	if (IS_ROOT(dentry)) {
		spin_unlock(&dentry->d_lock);
		return 1;
	}
	spin_unlock(&dentry->d_lock);

	esdfs_get_lower_path(dentry, &lower_path);
	lower_dentry = lower_path.dentry;
	esdfs_get_lower_parent(dentry, lower_dentry, &lower_parent_dentry);

	parent_dentry = dget_parent(dentry);
	esdfs_get_lower_path(parent_dentry, &lower_parent_path);

	if (lower_parent_path.dentry != lower_parent_dentry)
		goto drop;

	if (lower_dentry->d_flags & DCACHE_OP_REVALIDATE) {
		err = lower_dentry->d_op->d_revalidate(lower_dentry, flags);
		if (err == 0)
			goto drop;
	}

	/* can't do strcmp if lower is hashed */
	spin_lock(&lower_dentry->d_lock);
	if (d_unhashed(lower_dentry)) {
		spin_unlock(&lower_dentry->d_lock);
		goto drop;
	}

	spin_lock(&dentry->d_lock);

	if (!qstr_case_eq(&lower_dentry->d_name, &dentry->d_name)) {
		err = 0;
		__d_drop(dentry);	/* already holding spin lock */
	}

	spin_unlock(&dentry->d_lock);
	spin_unlock(&lower_dentry->d_lock);

	esdfs_revalidate_perms(dentry);
	if (ESDFS_DERIVE_PERMS(ESDFS_SB(dentry->d_sb)) &&
	    esdfs_derived_revalidate(dentry, parent_dentry))
		goto drop;

	goto out;

drop:
	d_drop(dentry);
	err = 0;
out:
	esdfs_put_lower_path(parent_dentry, &lower_parent_path);
	dput(parent_dentry);
	esdfs_put_lower_parent(dentry, &lower_parent_dentry);
	esdfs_put_lower_path(dentry, &lower_path);
	return err;
}

/* directly from fs/fat/namei_vfat.c */
static unsigned int __vfat_striptail_len(unsigned int len, const char *name)
{
	while (len && name[len - 1] == '.')
		len--;
	return len;
}

static unsigned int vfat_striptail_len(const struct qstr *qstr)
{
	return __vfat_striptail_len(qstr->len, qstr->name);
}


/* based on vfat_hashi() in fs/fat/namei_vfat.c (no code pages) */
static int esdfs_d_hash(const struct dentry *dentry, struct qstr *qstr)
{
	const unsigned char *name;
	unsigned int len;
	unsigned long hash;

	name = qstr->name;
	len = vfat_striptail_len(qstr);

	hash = init_name_hash(dentry);
	while (len--)
		hash = partial_name_hash(tolower(*name++), hash);
	qstr->hash = end_name_hash(hash);

	return 0;
}

/* based on vfat_cmpi() in fs/fat/namei_vfat.c (no code pages) */
static int esdfs_d_compare(const struct dentry *dentry, unsigned int len,
			   const char *str, const struct qstr *name)
{
	unsigned int alen, blen;

	/* A filename cannot end in '.' or we treat it like it has none */
	alen = vfat_striptail_len(name);
	blen = __vfat_striptail_len(len, str);
	if (alen == blen) {
		if (str_n_case_eq(name->name, str, alen))
			return 0;
	}
	return 1;
}

static void esdfs_d_release(struct dentry *dentry)
{
	if (!dentry || !dentry->d_fsdata)
		return;

	/* release and reset the lower paths */
	esdfs_put_reset_lower_paths(dentry);
	esdfs_release_lower_parent(dentry);
	esdfs_free_dentry_private_data(dentry);
}

static void esdfs_canonical_path(const struct path *path,
					struct path *actual_path) {
	if (ESDFS_DENTRY_HAS_STUB(path->dentry))
		esdfs_get_lower_stub_path(path->dentry, actual_path);
	else
		esdfs_get_lower_path(path->dentry, actual_path);
}

const struct dentry_operations esdfs_dops = {
	.d_revalidate	= esdfs_d_revalidate,
	.d_delete	= always_delete_dentry,
	.d_hash		= esdfs_d_hash,
	.d_compare	= esdfs_d_compare,
	.d_release	= esdfs_d_release,
	.d_canonical_path = esdfs_canonical_path,
};