text: // SPDX-License-Identifier: GPL-2.0
  /*
   * linux/drivers/staging/erofs/dir.c
   *
   * Copyright (C) 2017-2018 HUAWEI, Inc.
   *             http://www.huawei.com/
   * Created by Gao Xiang <gaoxiang25@huawei.com>
   *
   * This file is subject to the terms and conditions of the GNU General Public
   * License.  See the file COPYING in the main directory of the Linux
   * distribution for more details.
   */
  #include "internal.h"
  
  static const unsigned char erofs_filetype_table[EROFS_FT_MAX] = {
  	[EROFS_FT_UNKNOWN]	= DT_UNKNOWN,
  	[EROFS_FT_REG_FILE]	= DT_REG,
  	[EROFS_FT_DIR]		= DT_DIR,
  	[EROFS_FT_CHRDEV]	= DT_CHR,
  	[EROFS_FT_BLKDEV]	= DT_BLK,
  	[EROFS_FT_FIFO]		= DT_FIFO,
  	[EROFS_FT_SOCK]		= DT_SOCK,
  	[EROFS_FT_SYMLINK]	= DT_LNK,
  };
  
  static int erofs_fill_dentries(struct dir_context *ctx,
  	void *dentry_blk, unsigned int *ofs,
  	unsigned int nameoff, unsigned int maxsize)
  {
  	struct erofs_dirent *de = dentry_blk;
  	const struct erofs_dirent *end = dentry_blk + nameoff;
  
  	de = dentry_blk + *ofs;
  	while (de < end) {
  		const char *de_name;
  		int de_namelen;
  		unsigned char d_type;
  #ifdef CONFIG_EROFS_FS_DEBUG
  		unsigned int dbg_namelen;
  		unsigned char dbg_namebuf[EROFS_NAME_LEN];
  #endif
  
  		if (unlikely(de->file_type < EROFS_FT_MAX))
  			d_type = erofs_filetype_table[de->file_type];
  		else
  			d_type = DT_UNKNOWN;
  
  		nameoff = le16_to_cpu(de->nameoff);
  		de_name = (char *)dentry_blk + nameoff;
  
  		de_namelen = unlikely(de + 1 >= end) ?
  			/* last directory entry */
  			strnlen(de_name, maxsize - nameoff) :
  			le16_to_cpu(de[1].nameoff) - nameoff;
  
  		/* the corrupted directory found */
  		BUG_ON(de_namelen < 0);
  
  #ifdef CONFIG_EROFS_FS_DEBUG
  		dbg_namelen = min(EROFS_NAME_LEN - 1, de_namelen);
  		memcpy(dbg_namebuf, de_name, dbg_namelen);
  		dbg_namebuf[dbg_namelen] = '\0';
  
  		debugln("%s, found de_name %s de_len %d d_type %d", __func__,
  			dbg_namebuf, de_namelen, d_type);
  #endif
  
  		if (!dir_emit(ctx, de_name, de_namelen,
  					le64_to_cpu(de->nid), d_type))
  			/* stoped by some reason */
  			return 1;
  		++de;
  		*ofs += sizeof(struct erofs_dirent);
  	}
  	*ofs = maxsize;
  	return 0;
  }
  
  static int erofs_readdir(struct file *f, struct dir_context *ctx)
  {
  	struct inode *dir = file_inode(f);
  	struct address_space *mapping = dir->i_mapping;
  	const size_t dirsize = i_size_read(dir);
  	unsigned int i = ctx->pos / EROFS_BLKSIZ;
  	unsigned int ofs = ctx->pos % EROFS_BLKSIZ;
  	int err = 0;
  	bool initial = true;
  
  	while (ctx->pos < dirsize) {
  		struct page *dentry_page;
  		struct erofs_dirent *de;
  		unsigned int nameoff, maxsize;
  
  		dentry_page = read_mapping_page(mapping, i, NULL);
  		if (IS_ERR(dentry_page))
  			continue;
  
  		lock_page(dentry_page);
  		de = (struct erofs_dirent *)kmap(dentry_page);
  
  		nameoff = le16_to_cpu(de->nameoff);
  
  		if (unlikely(nameoff < sizeof(struct erofs_dirent) ||
  			nameoff >= PAGE_SIZE)) {
  			errln("%s, invalid de[0].nameoff %u",
  				__func__, nameoff);
  
  			err = -EIO;
  			goto skip_this;
  		}
  
  		maxsize = min_t(unsigned int,
  				dirsize - ctx->pos + ofs, PAGE_SIZE);
  
  		/* search dirents at the arbitrary position */
  		if (unlikely(initial)) {
  			initial = false;
  
  			ofs = roundup(ofs, sizeof(struct erofs_dirent));
  			if (unlikely(ofs >= nameoff))
  				goto skip_this;
  		}
  
  		err = erofs_fill_dentries(ctx, de, &ofs, nameoff, maxsize);
  skip_this:
  		kunmap(dentry_page);
  
  		unlock_page(dentry_page);
  		put_page(dentry_page);
  
  		ctx->pos = blknr_to_addr(i) + ofs;
  
  		if (unlikely(err))
  			break;
  		++i;
  		ofs = 0;
  	}
  	return err < 0 ? err : 0;
  }
  
  const struct file_operations erofs_dir_fops = {
  	.llseek		= generic_file_llseek,
  	.read		= generic_read_dir,
  	.iterate	= erofs_readdir,
  };
  
  