// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2017-2018 HUAWEI, Inc.
 *             https://www.huawei.com/
 * Copyright (C) 2022, Alibaba Cloud
 */
#include "internal.h"
#include <linux/filelock.h>

static int erofs_fill_dentries(struct inode *dir, struct dir_context *ctx,
                               void *dentry_blk, struct erofs_dirent *de,
                               unsigned int nameoff0, unsigned int maxsize)
{
        const struct erofs_dirent *end = dentry_blk + nameoff0;

        while (de < end) {
                unsigned char d_type = fs_ftype_to_dtype(de->file_type);
                unsigned int nameoff = le16_to_cpu(de->nameoff);
                const char *de_name = (char *)dentry_blk + nameoff;
                unsigned int de_namelen;

                /* the last dirent in the block? */
                if (de + 1 >= end)
                        de_namelen = strnlen(de_name, maxsize - nameoff);
                else
                        de_namelen = le16_to_cpu(de[1].nameoff) - nameoff;

                /* a corrupted entry is found */
                if (nameoff + de_namelen > maxsize ||
                    de_namelen > EROFS_NAME_LEN) {
                        erofs_err(dir->i_sb, "bogus dirent @ nid %llu",
                                  EROFS_I(dir)->nid);
                        DBG_BUGON(1);
                        return -EFSCORRUPTED;
                }

                if (!dir_emit(ctx, de_name, de_namelen,
                              erofs_nid_to_ino64(EROFS_SB(dir->i_sb),
                                                 le64_to_cpu(de->nid)), d_type))
                        return 1;
                ++de;
                ctx->pos += sizeof(struct erofs_dirent);
        }
        return 0;
}

static int erofs_readdir(struct file *f, struct dir_context *ctx)
{
        struct inode *dir = file_inode(f);
        struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
        struct super_block *sb = dir->i_sb;
        struct file_ra_state *ra = &f->f_ra;
        unsigned long bsz = sb->s_blocksize;
        unsigned int ofs = erofs_blkoff(sb, ctx->pos);
        pgoff_t ra_pages = DIV_ROUND_UP_POW2(
                        EROFS_I_SB(dir)->dir_ra_bytes, PAGE_SIZE);
        pgoff_t nr_pages = DIV_ROUND_UP_POW2(dir->i_size, PAGE_SIZE);
        int err = 0;
        bool initial = true;

        buf.mapping = dir->i_mapping;
        while (ctx->pos < dir->i_size) {
                erofs_off_t dbstart = ctx->pos - ofs;
                struct erofs_dirent *de;
                unsigned int nameoff, maxsize;

                if (fatal_signal_pending(current)) {
                        err = -ERESTARTSYS;
                        break;
                }

                /* readahead blocks to enhance performance for large directories */
                if (ra_pages) {
                        pgoff_t idx = DIV_ROUND_UP_POW2(ctx->pos, PAGE_SIZE);
                        pgoff_t pages = min(nr_pages - idx, ra_pages);

                        if (pages > 1 && !ra_has_index(ra, idx))
                                page_cache_sync_readahead(dir->i_mapping, ra,
                                                          f, idx, pages);
                }

                de = erofs_bread(&buf, dbstart, true);
                if (IS_ERR(de)) {
                        erofs_err(sb, "failed to readdir of logical block %llu of nid %llu",
                                  erofs_blknr(sb, dbstart), EROFS_I(dir)->nid);
                        err = PTR_ERR(de);
                        break;
                }

                nameoff = le16_to_cpu(de->nameoff);
                if (nameoff < sizeof(struct erofs_dirent) || nameoff >= bsz) {
                        erofs_err(sb, "invalid de[0].nameoff %u @ nid %llu",
                                  nameoff, EROFS_I(dir)->nid);
                        err = -EFSCORRUPTED;
                        break;
                }

                maxsize = min_t(unsigned int, dir->i_size - dbstart, bsz);
                /* search dirents at the arbitrary position */
                if (initial) {
                        initial = false;
                        ofs = roundup(ofs, sizeof(struct erofs_dirent));
                        ctx->pos = dbstart + ofs;
                }

                err = erofs_fill_dentries(dir, ctx, de, (void *)de + ofs,
                                          nameoff, maxsize);
                if (err)
                        break;
                ctx->pos = dbstart + maxsize;
                ofs = 0;
                cond_resched();
        }
        erofs_put_metabuf(&buf);
        if (EROFS_I(dir)->dot_omitted && ctx->pos == dir->i_size) {
                if (!dir_emit_dot(f, ctx))
                        return 0;
                ++ctx->pos;
        }
        return err < 0 ? err : 0;
}

const struct file_operations erofs_dir_fops = {
        .llseek         = generic_file_llseek,
        .read           = generic_read_dir,
        .iterate_shared = erofs_readdir,
        .unlocked_ioctl = erofs_ioctl,
#ifdef CONFIG_COMPAT
        .compat_ioctl   = erofs_compat_ioctl,
#endif
        .setlease       = generic_setlease,
};