fs/xfs/xfs_dir2_readdir.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (c) 2000-2005 Silicon Graphics, Inc.
  * Copyright (c) 2013 Red Hat, Inc.
  * All Rights Reserved.
  */
 #include "xfs.h"
 #include "xfs_fs.h"
 #include "xfs_shared.h"
 #include "xfs_format.h"
 #include "xfs_log_format.h"
 #include "xfs_trans_resv.h"
 #include "xfs_mount.h"
 #include "xfs_inode.h"
 #include "xfs_dir2.h"
 #include "xfs_dir2_priv.h"
 #include "xfs_trace.h"
 #include "xfs_bmap.h"
 #include "xfs_trans.h"
 #include "xfs_error.h"

 /*
  * Directory file type support functions
  */
 static unsigned char xfs_dir3_filetype_table[] = {
 	DT_UNKNOWN, DT_REG, DT_DIR, DT_CHR, DT_BLK,
 	DT_FIFO, DT_SOCK, DT_LNK, DT_WHT,
 };

 unsigned char
 xfs_dir3_get_dtype(
 	struct xfs_mount	*mp,
 	uint8_t			filetype)
 {
 	if (!xfs_has_ftype(mp))
 		return DT_UNKNOWN;

 	if (filetype >= XFS_DIR3_FT_MAX)
 		return DT_UNKNOWN;

 	return xfs_dir3_filetype_table[filetype];
 }

 STATIC int
 xfs_dir2_sf_getdents(
 	struct xfs_da_args	*args,
 	struct dir_context	*ctx)
 {
 	int			i;		/* shortform entry number */
 	struct xfs_inode	*dp = args->dp;	/* incore directory inode */
 	struct xfs_mount	*mp = dp->i_mount;
 	xfs_dir2_dataptr_t	off;		/* current entry's offset */
 	xfs_dir2_sf_entry_t	*sfep;		/* shortform directory entry */
 	xfs_dir2_sf_hdr_t	*sfp;		/* shortform structure */
 	xfs_dir2_dataptr_t	dot_offset;
 	xfs_dir2_dataptr_t	dotdot_offset;
 	xfs_ino_t		ino;
 	struct xfs_da_geometry	*geo = args->geo;

 	ASSERT(dp->i_df.if_format == XFS_DINODE_FMT_LOCAL);
 	ASSERT(dp->i_df.if_bytes == dp->i_disk_size);
 	ASSERT(dp->i_df.if_u1.if_data != NULL);

 	sfp = (xfs_dir2_sf_hdr_t *)dp->i_df.if_u1.if_data;

 	/*
 	 * If the block number in the offset is out of range, we're done.
 	 */
 	if (xfs_dir2_dataptr_to_db(geo, ctx->pos) > geo->datablk)
 		return 0;

 	/*
 	 * Precalculate offsets for "." and ".." as we will always need them.
 	 * This relies on the fact that directories always start with the
 	 * entries for "." and "..".
 	 */
 	dot_offset = xfs_dir2_db_off_to_dataptr(geo, geo->datablk,
 			geo->data_entry_offset);
 	dotdot_offset = xfs_dir2_db_off_to_dataptr(geo, geo->datablk,
 			geo->data_entry_offset +
 			xfs_dir2_data_entsize(mp, sizeof(".") - 1));

 	/*
 	 * Put . entry unless we're starting past it.
 	 */
 	if (ctx->pos <= dot_offset) {
 		ctx->pos = dot_offset & 0x7fffffff;
 		if (!dir_emit(ctx, ".", 1, dp->i_ino, DT_DIR))
 			return 0;
 	}

 	/*
 	 * Put .. entry unless we're starting past it.
 	 */
 	if (ctx->pos <= dotdot_offset) {
 		ino = xfs_dir2_sf_get_parent_ino(sfp);
 		ctx->pos = dotdot_offset & 0x7fffffff;
 		if (!dir_emit(ctx, "..", 2, ino, DT_DIR))
 			return 0;
 	}

 	/*
 	 * Loop while there are more entries and put'ing works.
 	 */
 	sfep = xfs_dir2_sf_firstentry(sfp);
 	for (i = 0; i < sfp->count; i++) {
 		uint8_t filetype;

 		off = xfs_dir2_db_off_to_dataptr(geo, geo->datablk,
 				xfs_dir2_sf_get_offset(sfep));

 		if (ctx->pos > off) {
 			sfep = xfs_dir2_sf_nextentry(mp, sfp, sfep);
 			continue;
 		}

 		ino = xfs_dir2_sf_get_ino(mp, sfp, sfep);
 		filetype = xfs_dir2_sf_get_ftype(mp, sfep);
 		ctx->pos = off & 0x7fffffff;
 		if (XFS_IS_CORRUPT(dp->i_mount,
 				   !xfs_dir2_namecheck(sfep->name,
 						       sfep->namelen)))
 			return -EFSCORRUPTED;
 		if (!dir_emit(ctx, (char *)sfep->name, sfep->namelen, ino,
 			    xfs_dir3_get_dtype(mp, filetype)))
 			return 0;
 		sfep = xfs_dir2_sf_nextentry(mp, sfp, sfep);
 	}

 	ctx->pos = xfs_dir2_db_off_to_dataptr(geo, geo->datablk + 1, 0) &
 								0x7fffffff;
 	return 0;
 }

 /*
  * Readdir for block directories.
  */
 STATIC int
 xfs_dir2_block_getdents(
 	struct xfs_da_args	*args,
 	struct dir_context	*ctx,
 	unsigned int		*lock_mode)
 {
 	struct xfs_inode	*dp = args->dp;	/* incore directory inode */
 	struct xfs_buf		*bp;		/* buffer for block */
 	int			error;		/* error return value */
 	int			wantoff;	/* starting block offset */
 	xfs_off_t		cook;
 	struct xfs_da_geometry	*geo = args->geo;
 	unsigned int		offset, next_offset;
 	unsigned int		end;

 	/*
 	 * If the block number in the offset is out of range, we're done.
 	 */
 	if (xfs_dir2_dataptr_to_db(geo, ctx->pos) > geo->datablk)
 		return 0;

 	error = xfs_dir3_block_read(args->trans, dp, &bp);
 	if (error)
 		return error;

 	xfs_iunlock(dp, *lock_mode);
 	*lock_mode = 0;

 	/*
 	 * Extract the byte offset we start at from the seek pointer.
 	 * We'll skip entries before this.
 	 */
 	wantoff = xfs_dir2_dataptr_to_off(geo, ctx->pos);
 	xfs_dir3_data_check(dp, bp);

 	/*
 	 * Loop over the data portion of the block.
 	 * Each object is a real entry (dep) or an unused one (dup).
 	 */
 	end = xfs_dir3_data_end_offset(geo, bp->b_addr);
 	for (offset = geo->data_entry_offset;
 	     offset < end;
 	     offset = next_offset) {
 		struct xfs_dir2_data_unused	*dup = bp->b_addr + offset;
 		struct xfs_dir2_data_entry	*dep = bp->b_addr + offset;
 		uint8_t filetype;

 		/*
 		 * Unused, skip it.
 		 */
 		if (be16_to_cpu(dup->freetag) == XFS_DIR2_DATA_FREE_TAG) {
 			next_offset = offset + be16_to_cpu(dup->length);
 			continue;
 		}

 		/*
 		 * Bump pointer for the next iteration.
 		 */
 		next_offset = offset +
 			xfs_dir2_data_entsize(dp->i_mount, dep->namelen);

 		/*
 		 * The entry is before the desired starting point, skip it.
 		 */
 		if (offset < wantoff)
 			continue;

 		cook = xfs_dir2_db_off_to_dataptr(geo, geo->datablk, offset);

 		ctx->pos = cook & 0x7fffffff;
 		filetype = xfs_dir2_data_get_ftype(dp->i_mount, dep);
 		/*
 		 * If it didn't fit, set the final offset to here & return.
 		 */
 		if (XFS_IS_CORRUPT(dp->i_mount,
 				   !xfs_dir2_namecheck(dep->name,
 						       dep->namelen))) {
 			error = -EFSCORRUPTED;
 			goto out_rele;
 		}
 		if (!dir_emit(ctx, (char *)dep->name, dep->namelen,
 			    be64_to_cpu(dep->inumber),
 			    xfs_dir3_get_dtype(dp->i_mount, filetype)))
 			goto out_rele;
 	}

 	/*
 	 * Reached the end of the block.
 	 * Set the offset to a non-existent block 1 and return.
 	 */
 	ctx->pos = xfs_dir2_db_off_to_dataptr(geo, geo->datablk + 1, 0) &
 								0x7fffffff;
 out_rele:
 	xfs_trans_brelse(args->trans, bp);
 	return error;
 }

 /*
  * Read a directory block and initiate readahead for blocks beyond that.
  * We maintain a sliding readahead window of the remaining space in the
  * buffer rounded up to the nearest block.
  */
 STATIC int
 xfs_dir2_leaf_readbuf(
 	struct xfs_da_args	*args,
 	size_t			bufsize,
 	xfs_dir2_off_t		*cur_off,
 	xfs_dablk_t		*ra_blk,
 	struct xfs_buf		**bpp)
 {
 	struct xfs_inode	*dp = args->dp;
 	struct xfs_buf		*bp = NULL;
 	struct xfs_da_geometry	*geo = args->geo;
 	struct xfs_ifork	*ifp = xfs_ifork_ptr(dp, XFS_DATA_FORK);
 	struct xfs_bmbt_irec	map;
 	struct blk_plug		plug;
 	xfs_dir2_off_t		new_off;
 	xfs_dablk_t		next_ra;
 	xfs_dablk_t		map_off;
 	xfs_dablk_t		last_da;
 	struct xfs_iext_cursor	icur;
 	int			ra_want;
 	int			error = 0;

 	error = xfs_iread_extents(args->trans, dp, XFS_DATA_FORK);
 	if (error)
 		goto out;

 	/*
 	 * Look for mapped directory blocks at or above the current offset.
 	 * Truncate down to the nearest directory block to start the scanning
 	 * operation.
 	 */
 	last_da = xfs_dir2_byte_to_da(geo, XFS_DIR2_LEAF_OFFSET);
 	map_off = xfs_dir2_db_to_da(geo, xfs_dir2_byte_to_db(geo, *cur_off));
 	if (!xfs_iext_lookup_extent(dp, ifp, map_off, &icur, &map))
 		goto out;
 	if (map.br_startoff >= last_da)
 		goto out;
 	xfs_trim_extent(&map, map_off, last_da - map_off);

 	/* Read the directory block of that first mapping. */
 	new_off = xfs_dir2_da_to_byte(geo, map.br_startoff);
 	if (new_off > *cur_off)
 		*cur_off = new_off;
 	error = xfs_dir3_data_read(args->trans, dp, map.br_startoff, 0, &bp);
 	if (error)
 		goto out;

 	/*
 	 * Start readahead for the next bufsize's worth of dir data blocks.
 	 * We may have already issued readahead for some of that range;
 	 * ra_blk tracks the last block we tried to read(ahead).
 	 */
 	ra_want = howmany(bufsize + geo->blksize, (1 << geo->fsblog));
 	if (*ra_blk >= last_da)
 		goto out;
 	else if (*ra_blk == 0)
 		*ra_blk = map.br_startoff;
 	next_ra = map.br_startoff + geo->fsbcount;
 	if (next_ra >= last_da)
 		goto out_no_ra;
 	if (map.br_blockcount < geo->fsbcount &&
 	    !xfs_iext_next_extent(ifp, &icur, &map))
 		goto out_no_ra;
 	if (map.br_startoff >= last_da)
 		goto out_no_ra;
 	xfs_trim_extent(&map, next_ra, last_da - next_ra);

 	/* Start ra for each dir (not fs) block that has a mapping. */
 	blk_start_plug(&plug);
 	while (ra_want > 0) {
 		next_ra = roundup((xfs_dablk_t)map.br_startoff, geo->fsbcount);
 		while (ra_want > 0 &&
 		       next_ra < map.br_startoff + map.br_blockcount) {
 			if (next_ra >= last_da) {
 				*ra_blk = last_da;
 				break;
 			}
 			if (next_ra > *ra_blk) {
 				xfs_dir3_data_readahead(dp, next_ra,
 							XFS_DABUF_MAP_HOLE_OK);
 				*ra_blk = next_ra;
 			}
 			ra_want -= geo->fsbcount;
 			next_ra += geo->fsbcount;
 		}
 		if (!xfs_iext_next_extent(ifp, &icur, &map)) {
 			*ra_blk = last_da;
 			break;
 		}
 	}
 	blk_finish_plug(&plug);

 out:
 	*bpp = bp;
 	return error;
 out_no_ra:
 	*ra_blk = last_da;
 	goto out;
 }

 /*
  * Getdents (readdir) for leaf and node directories.
  * This reads the data blocks only, so is the same for both forms.
  */
 STATIC int
 xfs_dir2_leaf_getdents(
 	struct xfs_da_args	*args,
 	struct dir_context	*ctx,
 	size_t			bufsize,
 	unsigned int		*lock_mode)
 {
 	struct xfs_inode	*dp = args->dp;
 	struct xfs_mount	*mp = dp->i_mount;
 	struct xfs_buf		*bp = NULL;	/* data block buffer */
 	xfs_dir2_data_entry_t	*dep;		/* data entry */
 	xfs_dir2_data_unused_t	*dup;		/* unused entry */
 	struct xfs_da_geometry	*geo = args->geo;
 	xfs_dablk_t		rablk = 0;	/* current readahead block */
 	xfs_dir2_off_t		curoff;		/* current overall offset */
 	int			length;		/* temporary length value */
 	int			byteoff;	/* offset in current block */
 	unsigned int		offset = 0;
 	int			error = 0;	/* error return value */

 	/*
 	 * If the offset is at or past the largest allowed value,
 	 * give up right away.
 	 */
 	if (ctx->pos >= XFS_DIR2_MAX_DATAPTR)
 		return 0;

 	/*
 	 * Inside the loop we keep the main offset value as a byte offset
 	 * in the directory file.
 	 */
 	curoff = xfs_dir2_dataptr_to_byte(ctx->pos);

 	/*
 	 * Loop over directory entries until we reach the end offset.
 	 * Get more blocks and readahead as necessary.
 	 */
 	while (curoff < XFS_DIR2_LEAF_OFFSET) {
 		uint8_t filetype;

 		/*
 		 * If we have no buffer, or we're off the end of the
 		 * current buffer, need to get another one.
 		 */
 		if (!bp || offset >= geo->blksize) {
 			if (bp) {
 				xfs_trans_brelse(args->trans, bp);
 				bp = NULL;
 			}

 			if (*lock_mode == 0)
 				*lock_mode = xfs_ilock_data_map_shared(dp);
 			error = xfs_dir2_leaf_readbuf(args, bufsize, &curoff,
 					&rablk, &bp);
 			if (error || !bp)
 				break;

 			xfs_iunlock(dp, *lock_mode);
 			*lock_mode = 0;

 			xfs_dir3_data_check(dp, bp);
 			/*
 			 * Find our position in the block.
 			 */
 			offset = geo->data_entry_offset;
 			byteoff = xfs_dir2_byte_to_off(geo, curoff);
 			/*
 			 * Skip past the header.
 			 */
 			if (byteoff == 0)
 				curoff += geo->data_entry_offset;
 			/*
 			 * Skip past entries until we reach our offset.
 			 */
 			else {
 				while (offset < byteoff) {
 					dup = bp->b_addr + offset;

 					if (be16_to_cpu(dup->freetag)
 						  == XFS_DIR2_DATA_FREE_TAG) {

 						length = be16_to_cpu(dup->length);
 						offset += length;
 						continue;
 					}
 					dep = bp->b_addr + offset;
 					length = xfs_dir2_data_entsize(mp,
 							dep->namelen);
 					offset += length;
 				}
 				/*
 				 * Now set our real offset.
 				 */
 				curoff =
 					xfs_dir2_db_off_to_byte(geo,
 					    xfs_dir2_byte_to_db(geo, curoff),
 					    offset);
 				if (offset >= geo->blksize)
 					continue;
 			}
 		}

 		/*
 		 * We have a pointer to an entry.  Is it a live one?
 		 */
 		dup = bp->b_addr + offset;

 		/*
 		 * No, it's unused, skip over it.
 		 */
 		if (be16_to_cpu(dup->freetag) == XFS_DIR2_DATA_FREE_TAG) {
 			length = be16_to_cpu(dup->length);
 			offset += length;
 			curoff += length;
 			continue;
 		}

 		dep = bp->b_addr + offset;
 		length = xfs_dir2_data_entsize(mp, dep->namelen);
 		filetype = xfs_dir2_data_get_ftype(mp, dep);

 		ctx->pos = xfs_dir2_byte_to_dataptr(curoff) & 0x7fffffff;
 		if (XFS_IS_CORRUPT(dp->i_mount,
 				   !xfs_dir2_namecheck(dep->name,
 						       dep->namelen))) {
 			error = -EFSCORRUPTED;
 			break;
 		}
 		if (!dir_emit(ctx, (char *)dep->name, dep->namelen,
 			    be64_to_cpu(dep->inumber),
 			    xfs_dir3_get_dtype(dp->i_mount, filetype)))
 			break;

 		/*
 		 * Advance to next entry in the block.
 		 */
 		offset += length;
 		curoff += length;
 		/* bufsize may have just been a guess; don't go negative */
 		bufsize = bufsize > length ? bufsize - length : 0;
 	}

 	/*
 	 * All done.  Set output offset value to current offset.
 	 */
 	if (curoff > xfs_dir2_dataptr_to_byte(XFS_DIR2_MAX_DATAPTR))
 		ctx->pos = XFS_DIR2_MAX_DATAPTR & 0x7fffffff;
 	else
 		ctx->pos = xfs_dir2_byte_to_dataptr(curoff) & 0x7fffffff;
 	if (bp)
 		xfs_trans_brelse(args->trans, bp);
 	return error;
 }

 /*
  * Read a directory.
  *
  * If supplied, the transaction collects locked dir buffers to avoid
  * nested buffer deadlocks.  This function does not dirty the
  * transaction.  The caller must hold the IOLOCK (shared or exclusive)
  * before calling this function.
  */
 int
 xfs_readdir(
 	struct xfs_trans	*tp,
 	struct xfs_inode	*dp,
 	struct dir_context	*ctx,
 	size_t			bufsize)
 {
 	struct xfs_da_args	args = { NULL };
 	unsigned int		lock_mode;
 	bool			isblock;
 	int			error;

 	trace_xfs_readdir(dp);

 	if (xfs_is_shutdown(dp->i_mount))
 		return -EIO;

 	ASSERT(S_ISDIR(VFS_I(dp)->i_mode));
 	ASSERT(xfs_isilocked(dp, XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
 	XFS_STATS_INC(dp->i_mount, xs_dir_getdents);

 	args.dp = dp;
 	args.geo = dp->i_mount->m_dir_geo;
 	args.trans = tp;

 	if (dp->i_df.if_format == XFS_DINODE_FMT_LOCAL)
 		return xfs_dir2_sf_getdents(&args, ctx);

 	lock_mode = xfs_ilock_data_map_shared(dp);
 	error = xfs_dir2_isblock(&args, &isblock);
 	if (error)
 		goto out_unlock;

 	if (isblock) {
 		error = xfs_dir2_block_getdents(&args, ctx, &lock_mode);
 		goto out_unlock;
 	}

 	error = xfs_dir2_leaf_getdents(&args, ctx, bufsize, &lock_mode);

 out_unlock:
 	if (lock_mode)
 		xfs_iunlock(dp, lock_mode);
 	return error;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Copyright (c) 2000-2005 Silicon Graphics, Inc.
	* Copyright (c) 2013 Red Hat, Inc.
	* All Rights Reserved.
	*/
	#include "xfs.h"
	#include "xfs_fs.h"
	#include "xfs_shared.h"
	#include "xfs_format.h"
	#include "xfs_log_format.h"
	#include "xfs_trans_resv.h"
	#include "xfs_mount.h"
	#include "xfs_inode.h"
	#include "xfs_dir2.h"
	#include "xfs_dir2_priv.h"
	#include "xfs_trace.h"
	#include "xfs_bmap.h"
	#include "xfs_trans.h"
	#include "xfs_error.h"

	/*
	* Directory file type support functions
	*/
	static unsigned char xfs_dir3_filetype_table[] = {
	DT_UNKNOWN, DT_REG, DT_DIR, DT_CHR, DT_BLK,
	DT_FIFO, DT_SOCK, DT_LNK, DT_WHT,
	};

	unsigned char
	xfs_dir3_get_dtype(
	struct xfs_mount *mp,
	uint8_t filetype)
	{
	if (!xfs_has_ftype(mp))
	return DT_UNKNOWN;

	if (filetype >= XFS_DIR3_FT_MAX)
	return DT_UNKNOWN;

	return xfs_dir3_filetype_table[filetype];
	}

	STATIC int
	xfs_dir2_sf_getdents(
	struct xfs_da_args *args,
	struct dir_context *ctx)
	{
	int i; /* shortform entry number */
	struct xfs_inode dp = args->dp; / incore directory inode */
	struct xfs_mount *mp = dp->i_mount;
	xfs_dir2_dataptr_t off; /* current entry's offset */
	xfs_dir2_sf_entry_t sfep; / shortform directory entry */
	xfs_dir2_sf_hdr_t sfp; / shortform structure */
	xfs_dir2_dataptr_t dot_offset;
	xfs_dir2_dataptr_t dotdot_offset;
	xfs_ino_t ino;
	struct xfs_da_geometry *geo = args->geo;

	ASSERT(dp->i_df.if_format == XFS_DINODE_FMT_LOCAL);
	ASSERT(dp->i_df.if_bytes == dp->i_disk_size);
	ASSERT(dp->i_df.if_u1.if_data != NULL);

	sfp = (xfs_dir2_sf_hdr_t *)dp->i_df.if_u1.if_data;

	/*
	* If the block number in the offset is out of range, we're done.
	*/
	if (xfs_dir2_dataptr_to_db(geo, ctx->pos) > geo->datablk)
	return 0;

	/*
	* Precalculate offsets for "." and ".." as we will always need them.
	* This relies on the fact that directories always start with the
	* entries for "." and "..".
	*/
	dot_offset = xfs_dir2_db_off_to_dataptr(geo, geo->datablk,
	geo->data_entry_offset);
	dotdot_offset = xfs_dir2_db_off_to_dataptr(geo, geo->datablk,
	geo->data_entry_offset +
	xfs_dir2_data_entsize(mp, sizeof(".") - 1));

	/*
	* Put . entry unless we're starting past it.
	*/
	if (ctx->pos <= dot_offset) {
	ctx->pos = dot_offset & 0x7fffffff;
	if (!dir_emit(ctx, ".", 1, dp->i_ino, DT_DIR))
	return 0;
	}

	/*
	* Put .. entry unless we're starting past it.
	*/
	if (ctx->pos <= dotdot_offset) {
	ino = xfs_dir2_sf_get_parent_ino(sfp);
	ctx->pos = dotdot_offset & 0x7fffffff;
	if (!dir_emit(ctx, "..", 2, ino, DT_DIR))
	return 0;
	}

	/*
	* Loop while there are more entries and put'ing works.
	*/
	sfep = xfs_dir2_sf_firstentry(sfp);
	for (i = 0; i < sfp->count; i++) {
	uint8_t filetype;

	off = xfs_dir2_db_off_to_dataptr(geo, geo->datablk,
	xfs_dir2_sf_get_offset(sfep));

	if (ctx->pos > off) {
	sfep = xfs_dir2_sf_nextentry(mp, sfp, sfep);
	continue;
	}

	ino = xfs_dir2_sf_get_ino(mp, sfp, sfep);
	filetype = xfs_dir2_sf_get_ftype(mp, sfep);
	ctx->pos = off & 0x7fffffff;
	if (XFS_IS_CORRUPT(dp->i_mount,
	!xfs_dir2_namecheck(sfep->name,
	sfep->namelen)))
	return -EFSCORRUPTED;
	if (!dir_emit(ctx, (char *)sfep->name, sfep->namelen, ino,
	xfs_dir3_get_dtype(mp, filetype)))
	return 0;
	sfep = xfs_dir2_sf_nextentry(mp, sfp, sfep);
	}

	ctx->pos = xfs_dir2_db_off_to_dataptr(geo, geo->datablk + 1, 0) &
	0x7fffffff;
	return 0;
	}

	/*
	* Readdir for block directories.
	*/
	STATIC int
	xfs_dir2_block_getdents(
	struct xfs_da_args *args,
	struct dir_context *ctx,
	unsigned int *lock_mode)
	{
	struct xfs_inode dp = args->dp; / incore directory inode */
	struct xfs_buf bp; / buffer for block */
	int error; /* error return value */
	int wantoff; /* starting block offset */
	xfs_off_t cook;
	struct xfs_da_geometry *geo = args->geo;
	unsigned int offset, next_offset;
	unsigned int end;

	/*
	* If the block number in the offset is out of range, we're done.
	*/
	if (xfs_dir2_dataptr_to_db(geo, ctx->pos) > geo->datablk)
	return 0;

	error = xfs_dir3_block_read(args->trans, dp, &bp);
	if (error)
	return error;

	xfs_iunlock(dp, *lock_mode);
	*lock_mode = 0;

	/*
	* Extract the byte offset we start at from the seek pointer.
	* We'll skip entries before this.
	*/
	wantoff = xfs_dir2_dataptr_to_off(geo, ctx->pos);
	xfs_dir3_data_check(dp, bp);

	/*
	* Loop over the data portion of the block.
	* Each object is a real entry (dep) or an unused one (dup).
	*/
	end = xfs_dir3_data_end_offset(geo, bp->b_addr);
	for (offset = geo->data_entry_offset;
	offset < end;
	offset = next_offset) {
	struct xfs_dir2_data_unused *dup = bp->b_addr + offset;
	struct xfs_dir2_data_entry *dep = bp->b_addr + offset;
	uint8_t filetype;

	/*
	* Unused, skip it.
	*/
	if (be16_to_cpu(dup->freetag) == XFS_DIR2_DATA_FREE_TAG) {
	next_offset = offset + be16_to_cpu(dup->length);
	continue;
	}

	/*
	* Bump pointer for the next iteration.
	*/
	next_offset = offset +
	xfs_dir2_data_entsize(dp->i_mount, dep->namelen);

	/*
	* The entry is before the desired starting point, skip it.
	*/
	if (offset < wantoff)
	continue;

	cook = xfs_dir2_db_off_to_dataptr(geo, geo->datablk, offset);

	ctx->pos = cook & 0x7fffffff;
	filetype = xfs_dir2_data_get_ftype(dp->i_mount, dep);
	/*
	* If it didn't fit, set the final offset to here & return.
	*/
	if (XFS_IS_CORRUPT(dp->i_mount,
	!xfs_dir2_namecheck(dep->name,
	dep->namelen))) {
	error = -EFSCORRUPTED;
	goto out_rele;
	}
	if (!dir_emit(ctx, (char *)dep->name, dep->namelen,
	be64_to_cpu(dep->inumber),
	xfs_dir3_get_dtype(dp->i_mount, filetype)))
	goto out_rele;
	}

	/*
	* Reached the end of the block.
	* Set the offset to a non-existent block 1 and return.
	*/
	ctx->pos = xfs_dir2_db_off_to_dataptr(geo, geo->datablk + 1, 0) &
	0x7fffffff;
	out_rele:
	xfs_trans_brelse(args->trans, bp);
	return error;
	}

	/*
	* Read a directory block and initiate readahead for blocks beyond that.
	* We maintain a sliding readahead window of the remaining space in the
	* buffer rounded up to the nearest block.
	*/
	STATIC int
	xfs_dir2_leaf_readbuf(
	struct xfs_da_args *args,
	size_t bufsize,
	xfs_dir2_off_t *cur_off,
	xfs_dablk_t *ra_blk,
	struct xfs_buf **bpp)
	{
	struct xfs_inode *dp = args->dp;
	struct xfs_buf *bp = NULL;
	struct xfs_da_geometry *geo = args->geo;
	struct xfs_ifork *ifp = xfs_ifork_ptr(dp, XFS_DATA_FORK);
	struct xfs_bmbt_irec map;
	struct blk_plug plug;
	xfs_dir2_off_t new_off;
	xfs_dablk_t next_ra;
	xfs_dablk_t map_off;
	xfs_dablk_t last_da;
	struct xfs_iext_cursor icur;
	int ra_want;
	int error = 0;

	error = xfs_iread_extents(args->trans, dp, XFS_DATA_FORK);
	if (error)
	goto out;

	/*
	* Look for mapped directory blocks at or above the current offset.
	* Truncate down to the nearest directory block to start the scanning
	* operation.
	*/
	last_da = xfs_dir2_byte_to_da(geo, XFS_DIR2_LEAF_OFFSET);
	map_off = xfs_dir2_db_to_da(geo, xfs_dir2_byte_to_db(geo, *cur_off));
	if (!xfs_iext_lookup_extent(dp, ifp, map_off, &icur, &map))
	goto out;
	if (map.br_startoff >= last_da)
	goto out;
	xfs_trim_extent(&map, map_off, last_da - map_off);

	/* Read the directory block of that first mapping. */
	new_off = xfs_dir2_da_to_byte(geo, map.br_startoff);
	if (new_off > *cur_off)
	*cur_off = new_off;
	error = xfs_dir3_data_read(args->trans, dp, map.br_startoff, 0, &bp);
	if (error)
	goto out;

	/*
	* Start readahead for the next bufsize's worth of dir data blocks.
	* We may have already issued readahead for some of that range;
	* ra_blk tracks the last block we tried to read(ahead).
	*/
	ra_want = howmany(bufsize + geo->blksize, (1 << geo->fsblog));
	if (*ra_blk >= last_da)
	goto out;
	else if (*ra_blk == 0)
	*ra_blk = map.br_startoff;
	next_ra = map.br_startoff + geo->fsbcount;
	if (next_ra >= last_da)
	goto out_no_ra;
	if (map.br_blockcount < geo->fsbcount &&
	!xfs_iext_next_extent(ifp, &icur, &map))
	goto out_no_ra;
	if (map.br_startoff >= last_da)
	goto out_no_ra;
	xfs_trim_extent(&map, next_ra, last_da - next_ra);

	/* Start ra for each dir (not fs) block that has a mapping. */
	blk_start_plug(&plug);
	while (ra_want > 0) {
	next_ra = roundup((xfs_dablk_t)map.br_startoff, geo->fsbcount);
	while (ra_want > 0 &&
	next_ra < map.br_startoff + map.br_blockcount) {
	if (next_ra >= last_da) {
	*ra_blk = last_da;
	break;
	}
	if (next_ra > *ra_blk) {
	xfs_dir3_data_readahead(dp, next_ra,
	XFS_DABUF_MAP_HOLE_OK);
	*ra_blk = next_ra;
	}
	ra_want -= geo->fsbcount;
	next_ra += geo->fsbcount;
	}
	if (!xfs_iext_next_extent(ifp, &icur, &map)) {
	*ra_blk = last_da;
	break;
	}
	}
	blk_finish_plug(&plug);

	out:
	*bpp = bp;
	return error;
	out_no_ra:
	*ra_blk = last_da;
	goto out;
	}

	/*
	* Getdents (readdir) for leaf and node directories.
	* This reads the data blocks only, so is the same for both forms.
	*/
	STATIC int
	xfs_dir2_leaf_getdents(
	struct xfs_da_args *args,
	struct dir_context *ctx,
	size_t bufsize,
	unsigned int *lock_mode)
	{
	struct xfs_inode *dp = args->dp;
	struct xfs_mount *mp = dp->i_mount;
	struct xfs_buf bp = NULL; / data block buffer */
	xfs_dir2_data_entry_t dep; / data entry */
	xfs_dir2_data_unused_t dup; / unused entry */
	struct xfs_da_geometry *geo = args->geo;
	xfs_dablk_t rablk = 0; /* current readahead block */
	xfs_dir2_off_t curoff; /* current overall offset */
	int length; /* temporary length value */
	int byteoff; /* offset in current block */
	unsigned int offset = 0;
	int error = 0; /* error return value */

	/*
	* If the offset is at or past the largest allowed value,
	* give up right away.
	*/
	if (ctx->pos >= XFS_DIR2_MAX_DATAPTR)
	return 0;

	/*
	* Inside the loop we keep the main offset value as a byte offset
	* in the directory file.
	*/
	curoff = xfs_dir2_dataptr_to_byte(ctx->pos);

	/*
	* Loop over directory entries until we reach the end offset.
	* Get more blocks and readahead as necessary.
	*/
	while (curoff < XFS_DIR2_LEAF_OFFSET) {
	uint8_t filetype;

	/*
	* If we have no buffer, or we're off the end of the
	* current buffer, need to get another one.
	*/
	if (!bp \|\| offset >= geo->blksize) {
	if (bp) {
	xfs_trans_brelse(args->trans, bp);
	bp = NULL;
	}

	if (*lock_mode == 0)
	*lock_mode = xfs_ilock_data_map_shared(dp);
	error = xfs_dir2_leaf_readbuf(args, bufsize, &curoff,
	&rablk, &bp);
	if (error \|\| !bp)
	break;

	xfs_iunlock(dp, *lock_mode);
	*lock_mode = 0;

	xfs_dir3_data_check(dp, bp);
	/*
	* Find our position in the block.
	*/
	offset = geo->data_entry_offset;
	byteoff = xfs_dir2_byte_to_off(geo, curoff);
	/*
	* Skip past the header.
	*/
	if (byteoff == 0)
	curoff += geo->data_entry_offset;
	/*
	* Skip past entries until we reach our offset.
	*/
	else {
	while (offset < byteoff) {
	dup = bp->b_addr + offset;

	if (be16_to_cpu(dup->freetag)
	== XFS_DIR2_DATA_FREE_TAG) {

	length = be16_to_cpu(dup->length);
	offset += length;
	continue;
	}
	dep = bp->b_addr + offset;
	length = xfs_dir2_data_entsize(mp,
	dep->namelen);
	offset += length;
	}
	/*
	* Now set our real offset.
	*/
	curoff =
	xfs_dir2_db_off_to_byte(geo,
	xfs_dir2_byte_to_db(geo, curoff),
	offset);
	if (offset >= geo->blksize)
	continue;
	}
	}

	/*
	* We have a pointer to an entry. Is it a live one?
	*/
	dup = bp->b_addr + offset;

	/*
	* No, it's unused, skip over it.
	*/
	if (be16_to_cpu(dup->freetag) == XFS_DIR2_DATA_FREE_TAG) {
	length = be16_to_cpu(dup->length);
	offset += length;
	curoff += length;
	continue;
	}

	dep = bp->b_addr + offset;
	length = xfs_dir2_data_entsize(mp, dep->namelen);
	filetype = xfs_dir2_data_get_ftype(mp, dep);

	ctx->pos = xfs_dir2_byte_to_dataptr(curoff) & 0x7fffffff;
	if (XFS_IS_CORRUPT(dp->i_mount,
	!xfs_dir2_namecheck(dep->name,
	dep->namelen))) {
	error = -EFSCORRUPTED;
	break;
	}
	if (!dir_emit(ctx, (char *)dep->name, dep->namelen,
	be64_to_cpu(dep->inumber),
	xfs_dir3_get_dtype(dp->i_mount, filetype)))
	break;

	/*
	* Advance to next entry in the block.
	*/
	offset += length;
	curoff += length;
	/* bufsize may have just been a guess; don't go negative */
	bufsize = bufsize > length ? bufsize - length : 0;
	}

	/*
	* All done. Set output offset value to current offset.
	*/
	if (curoff > xfs_dir2_dataptr_to_byte(XFS_DIR2_MAX_DATAPTR))
	ctx->pos = XFS_DIR2_MAX_DATAPTR & 0x7fffffff;
	else
	ctx->pos = xfs_dir2_byte_to_dataptr(curoff) & 0x7fffffff;
	if (bp)
	xfs_trans_brelse(args->trans, bp);
	return error;
	}

	/*
	* Read a directory.
	*
	* If supplied, the transaction collects locked dir buffers to avoid
	* nested buffer deadlocks. This function does not dirty the
	* transaction. The caller must hold the IOLOCK (shared or exclusive)
	* before calling this function.
	*/
	int
	xfs_readdir(
	struct xfs_trans *tp,
	struct xfs_inode *dp,
	struct dir_context *ctx,
	size_t bufsize)
	{
	struct xfs_da_args args = { NULL };
	unsigned int lock_mode;
	bool isblock;
	int error;

	trace_xfs_readdir(dp);

	if (xfs_is_shutdown(dp->i_mount))
	return -EIO;

	ASSERT(S_ISDIR(VFS_I(dp)->i_mode));
	ASSERT(xfs_isilocked(dp, XFS_IOLOCK_SHARED \| XFS_IOLOCK_EXCL));
	XFS_STATS_INC(dp->i_mount, xs_dir_getdents);

	args.dp = dp;
	args.geo = dp->i_mount->m_dir_geo;
	args.trans = tp;

	if (dp->i_df.if_format == XFS_DINODE_FMT_LOCAL)
	return xfs_dir2_sf_getdents(&args, ctx);

	lock_mode = xfs_ilock_data_map_shared(dp);
	error = xfs_dir2_isblock(&args, &isblock);
	if (error)
	goto out_unlock;

	if (isblock) {
	error = xfs_dir2_block_getdents(&args, ctx, &lock_mode);
	goto out_unlock;
	}

	error = xfs_dir2_leaf_getdents(&args, ctx, bufsize, &lock_mode);

	out_unlock:
	if (lock_mode)
	xfs_iunlock(dp, lock_mode);
	return error;
	}