// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Squashfs - a compressed read only filesystem for Linux
 *
 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
 * Phillip Lougher <phillip@squashfs.org.uk>
 *
 * dir.c
 */

/*
 * This file implements code to read directories from disk.
 *
 * See namei.c for a description of directory organisation on disk.
 */

#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/slab.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
#include "squashfs.h"

static const unsigned char squashfs_filetype_table[] = {
        DT_UNKNOWN, DT_DIR, DT_REG, DT_LNK, DT_BLK, DT_CHR, DT_FIFO, DT_SOCK
};

/*
 * Lookup offset (f_pos) in the directory index, returning the
 * metadata block containing it.
 *
 * If we get an error reading the index then return the part of the index
 * (if any) we have managed to read - the index isn't essential, just
 * quicker.
 */
static int get_dir_index_using_offset(struct super_block *sb,
        u64 *next_block, int *next_offset, u64 index_start, int index_offset,
        int i_count, u64 f_pos)
{
        struct squashfs_sb_info *msblk = sb->s_fs_info;
        int err, i, index, length = 0;
        unsigned int size;
        struct squashfs_dir_index dir_index;

        TRACE("Entered get_dir_index_using_offset, i_count %d, f_pos %lld\n",
                                        i_count, f_pos);

        /*
         * Translate from external f_pos to the internal f_pos.  This
         * is offset by 3 because we invent "." and ".." entries which are
         * not actually stored in the directory.
         */
        if (f_pos <= 3)
                return f_pos;
        f_pos -= 3;

        for (i = 0; i < i_count; i++) {
                err = squashfs_read_metadata(sb, &dir_index, &index_start,
                                &index_offset, sizeof(dir_index));
                if (err < 0)
                        break;

                index = le32_to_cpu(dir_index.index);
                if (index > f_pos)
                        /*
                         * Found the index we're looking for.
                         */
                        break;

                size = le32_to_cpu(dir_index.size) + 1;

                /* size should never be larger than SQUASHFS_NAME_LEN */
                if (size > SQUASHFS_NAME_LEN)
                        break;

                err = squashfs_read_metadata(sb, NULL, &index_start,
                                &index_offset, size);
                if (err < 0)
                        break;

                length = index;
                *next_block = le32_to_cpu(dir_index.start_block) +
                                        msblk->directory_table;
        }

        *next_offset = (length + *next_offset) % SQUASHFS_METADATA_SIZE;

        /*
         * Translate back from internal f_pos to external f_pos.
         */
        return length + 3;
}


static int squashfs_readdir(struct file *file, struct dir_context *ctx)
{
        struct inode *inode = file_inode(file);
        struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
        u64 block = squashfs_i(inode)->start + msblk->directory_table;
        int offset = squashfs_i(inode)->offset, length, err;
        unsigned int inode_number, dir_count, size, type;
        struct squashfs_dir_header dirh;
        struct squashfs_dir_entry *dire;

        TRACE("Entered squashfs_readdir [%llx:%x]\n", block, offset);

        dire = kmalloc(sizeof(*dire) + SQUASHFS_NAME_LEN + 1, GFP_KERNEL);
        if (dire == NULL) {
                ERROR("Failed to allocate squashfs_dir_entry\n");
                goto finish;
        }

        /*
         * Return "." and  ".." entries as the first two filenames in the
         * directory.  To maximise compression these two entries are not
         * stored in the directory, and so we invent them here.
         *
         * It also means that the external f_pos is offset by 3 from the
         * on-disk directory f_pos.
         */
        while (ctx->pos < 3) {
                char *name;
                int i_ino;

                if (ctx->pos == 0) {
                        name = ".";
                        size = 1;
                        i_ino = inode->i_ino;
                } else {
                        name = "..";
                        size = 2;
                        i_ino = squashfs_i(inode)->parent;
                }

                if (!dir_emit(ctx, name, size, i_ino,
                                squashfs_filetype_table[1]))
                        goto finish;

                ctx->pos += size;
        }

        length = get_dir_index_using_offset(inode->i_sb, &block, &offset,
                                squashfs_i(inode)->dir_idx_start,
                                squashfs_i(inode)->dir_idx_offset,
                                squashfs_i(inode)->dir_idx_cnt,
                                ctx->pos);

        while (length < i_size_read(inode)) {
                /*
                 * Read directory header
                 */
                err = squashfs_read_metadata(inode->i_sb, &dirh, &block,
                                        &offset, sizeof(dirh));
                if (err < 0)
                        goto failed_read;

                length += sizeof(dirh);

                dir_count = le32_to_cpu(dirh.count) + 1;

                if (dir_count > SQUASHFS_DIR_COUNT)
                        goto failed_read;

                while (dir_count--) {
                        /*
                         * Read directory entry.
                         */
                        err = squashfs_read_metadata(inode->i_sb, dire, &block,
                                        &offset, sizeof(*dire));
                        if (err < 0)
                                goto failed_read;

                        size = le16_to_cpu(dire->size) + 1;

                        /* size should never be larger than SQUASHFS_NAME_LEN */
                        if (size > SQUASHFS_NAME_LEN)
                                goto failed_read;

                        err = squashfs_read_metadata(inode->i_sb, dire->name,
                                        &block, &offset, size);
                        if (err < 0)
                                goto failed_read;

                        length += sizeof(*dire) + size;

                        if (ctx->pos >= length)
                                continue;

                        dire->name[size] = '\0';
                        inode_number = le32_to_cpu(dirh.inode_number) +
                                ((short) le16_to_cpu(dire->inode_number));
                        type = le16_to_cpu(dire->type);

                        if (type > SQUASHFS_MAX_DIR_TYPE)
                                goto failed_read;

                        if (!dir_emit(ctx, dire->name, size,
                                        inode_number,
                                        squashfs_filetype_table[type]))
                                goto finish;

                        ctx->pos = length;
                }
        }

finish:
        kfree(dire);
        return 0;

failed_read:
        ERROR("Unable to read directory block [%llx:%x]\n", block, offset);
        kfree(dire);
        return 0;
}


const struct file_operations squashfs_dir_ops = {
        .read = generic_read_dir,
        .iterate_shared = squashfs_readdir,
        .llseek = generic_file_llseek,
};