/* RomFS storage access routines
 *
 * Copyright © 2007 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 License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 */

#include <linux/fs.h>
#include <linux/mtd/super.h>
#include <linux/buffer_head.h>
#include "internal.h"

#if !defined(CONFIG_ROMFS_ON_MTD) && !defined(CONFIG_ROMFS_ON_BLOCK)
#error no ROMFS backing store interface configured
#endif

#ifdef CONFIG_ROMFS_ON_MTD
#define ROMFS_MTD_READ(sb, ...) ((sb)->s_mtd->read((sb)->s_mtd, ##__VA_ARGS__))

/*
 * read data from an romfs image on an MTD device
 */
static int romfs_mtd_read(struct super_block *sb, unsigned long pos,
                          void *buf, size_t buflen)
{
        size_t rlen;
        int ret;

        ret = ROMFS_MTD_READ(sb, pos, buflen, &rlen, buf);
        return (ret < 0 || rlen != buflen) ? -EIO : 0;
}

/*
 * determine the length of a string in a romfs image on an MTD device
 */
static ssize_t romfs_mtd_strnlen(struct super_block *sb,
                                 unsigned long pos, size_t maxlen)
{
        ssize_t n = 0;
        size_t segment;
        u_char buf[16], *p;
        size_t len;
        int ret;

        /* scan the string up to 16 bytes at a time */
        while (maxlen > 0) {
                segment = min_t(size_t, maxlen, 16);
                ret = ROMFS_MTD_READ(sb, pos, segment, &len, buf);
                if (ret < 0)
                        return ret;
                p = memchr(buf, 0, len);
                if (p)
                        return n + (p - buf);
                maxlen -= len;
                pos += len;
                n += len;
        }

        return n;
}

/*
 * compare a string to one in a romfs image on MTD
 * - return 1 if matched, 0 if differ, -ve if error
 */
static int romfs_mtd_strcmp(struct super_block *sb, unsigned long pos,
                            const char *str, size_t size)
{
        u_char buf[17];
        size_t len, segment;
        int ret;

        /* scan the string up to 16 bytes at a time, and attempt to grab the
         * trailing NUL whilst we're at it */
        buf[0] = 0xff;

        while (size > 0) {
                segment = min_t(size_t, size + 1, 17);
                ret = ROMFS_MTD_READ(sb, pos, segment, &len, buf);
                if (ret < 0)
                        return ret;
                len--;
                if (memcmp(buf, str, len) != 0)
                        return 0;
                buf[0] = buf[len];
                size -= len;
                pos += len;
                str += len;
        }

        /* check the trailing NUL was */
        if (buf[0])
                return 0;

        return 1;
}
#endif /* CONFIG_ROMFS_ON_MTD */

#ifdef CONFIG_ROMFS_ON_BLOCK
/*
 * read data from an romfs image on a block device
 */
static int romfs_blk_read(struct super_block *sb, unsigned long pos,
                          void *buf, size_t buflen)
{
        struct buffer_head *bh;
        unsigned long offset;
        size_t segment;

        /* copy the string up to blocksize bytes at a time */
        while (buflen > 0) {
                offset = pos & (ROMBSIZE - 1);
                segment = min_t(size_t, buflen, ROMBSIZE - offset);
                bh = sb_bread(sb, pos >> ROMBSBITS);
                if (!bh)
                        return -EIO;
                memcpy(buf, bh->b_data + offset, segment);
                brelse(bh);
                buf += segment;
                buflen -= segment;
                pos += segment;
        }

        return 0;
}

/*
 * determine the length of a string in romfs on a block device
 */
static ssize_t romfs_blk_strnlen(struct super_block *sb,
                                 unsigned long pos, size_t limit)
{
        struct buffer_head *bh;
        unsigned long offset;
        ssize_t n = 0;
        size_t segment;
        u_char *buf, *p;

        /* scan the string up to blocksize bytes at a time */
        while (limit > 0) {
                offset = pos & (ROMBSIZE - 1);
                segment = min_t(size_t, limit, ROMBSIZE - offset);
                bh = sb_bread(sb, pos >> ROMBSBITS);
                if (!bh)
                        return -EIO;
                buf = bh->b_data + offset;
                p = memchr(buf, 0, segment);
                brelse(bh);
                if (p)
                        return n + (p - buf);
                limit -= segment;
                pos += segment;
                n += segment;
        }

        return n;
}

/*
 * compare a string to one in a romfs image on a block device
 * - return 1 if matched, 0 if differ, -ve if error
 */
static int romfs_blk_strcmp(struct super_block *sb, unsigned long pos,
                            const char *str, size_t size)
{
        struct buffer_head *bh;
        unsigned long offset;
        size_t segment;
        bool matched, terminated = false;

        /* compare string up to a block at a time */
        while (size > 0) {
                offset = pos & (ROMBSIZE - 1);
                segment = min_t(size_t, size, ROMBSIZE - offset);
                bh = sb_bread(sb, pos >> ROMBSBITS);
                if (!bh)
                        return -EIO;
                matched = (memcmp(bh->b_data + offset, str, segment) == 0);

                size -= segment;
                pos += segment;
                str += segment;
                if (matched && size == 0 && offset + segment < ROMBSIZE) {
                        if (!bh->b_data[offset + segment])
                                terminated = true;
                        else
                                matched = false;
                }
                brelse(bh);
                if (!matched)
                        return 0;
        }

        if (!terminated) {
                /* the terminating NUL must be on the first byte of the next
                 * block */
                BUG_ON((pos & (ROMBSIZE - 1)) != 0);
                bh = sb_bread(sb, pos >> ROMBSBITS);
                if (!bh)
                        return -EIO;
                matched = !bh->b_data[0];
                brelse(bh);
                if (!matched)
                        return 0;
        }

        return 1;
}
#endif /* CONFIG_ROMFS_ON_BLOCK */

/*
 * read data from the romfs image
 */
int romfs_dev_read(struct super_block *sb, unsigned long pos,
                   void *buf, size_t buflen)
{
        size_t limit;

        limit = romfs_maxsize(sb);
        if (pos >= limit)
                return -EIO;
        if (buflen > limit - pos)
                buflen = limit - pos;

#ifdef CONFIG_ROMFS_ON_MTD
        if (sb->s_mtd)
                return romfs_mtd_read(sb, pos, buf, buflen);
#endif
#ifdef CONFIG_ROMFS_ON_BLOCK
        if (sb->s_bdev)
                return romfs_blk_read(sb, pos, buf, buflen);
#endif
        return -EIO;
}

/*
 * determine the length of a string in romfs
 */
ssize_t romfs_dev_strnlen(struct super_block *sb,
                          unsigned long pos, size_t maxlen)
{
        size_t limit;

        limit = romfs_maxsize(sb);
        if (pos >= limit)
                return -EIO;
        if (maxlen > limit - pos)
                maxlen = limit - pos;

#ifdef CONFIG_ROMFS_ON_MTD
        if (sb->s_mtd)
                return romfs_mtd_strnlen(sb, pos, maxlen);
#endif
#ifdef CONFIG_ROMFS_ON_BLOCK
        if (sb->s_bdev)
                return romfs_blk_strnlen(sb, pos, maxlen);
#endif
        return -EIO;
}

/*
 * compare a string to one in romfs
 * - the string to be compared to, str, may not be NUL-terminated; instead the
 *   string is of the specified size
 * - return 1 if matched, 0 if differ, -ve if error
 */
int romfs_dev_strcmp(struct super_block *sb, unsigned long pos,
                     const char *str, size_t size)
{
        size_t limit;

        limit = romfs_maxsize(sb);
        if (pos >= limit)
                return -EIO;
        if (size > ROMFS_MAXFN)
                return -ENAMETOOLONG;
        if (size + 1 > limit - pos)
                return -EIO;

#ifdef CONFIG_ROMFS_ON_MTD
        if (sb->s_mtd)
                return romfs_mtd_strcmp(sb, pos, str, size);
#endif
#ifdef CONFIG_ROMFS_ON_BLOCK
        if (sb->s_bdev)
                return romfs_blk_strcmp(sb, pos, str, size);
#endif
        return -EIO;
}