text: // SPDX-License-Identifier: GPL-2.0+
  /*
   * Copyright (C) 2017 Oracle.  All Rights Reserved.
   *
   * Author: Darrick J. Wong <darrick.wong@oracle.com>
   */
  #include "ext4.h"
  #include <linux/fsmap.h>
  #include "fsmap.h"
  #include "mballoc.h"
  #include <linux/sort.h>
  #include <linux/list_sort.h>
  #include <trace/events/ext4.h>
  
  /* Convert an ext4_fsmap to an fsmap. */
  void ext4_fsmap_from_internal(struct super_block *sb, struct fsmap *dest,
  			      struct ext4_fsmap *src)
  {
  	dest->fmr_device = src->fmr_device;
  	dest->fmr_flags = src->fmr_flags;
  	dest->fmr_physical = src->fmr_physical << sb->s_blocksize_bits;
  	dest->fmr_owner = src->fmr_owner;
  	dest->fmr_offset = 0;
  	dest->fmr_length = src->fmr_length << sb->s_blocksize_bits;
  	dest->fmr_reserved[0] = 0;
  	dest->fmr_reserved[1] = 0;
  	dest->fmr_reserved[2] = 0;
  }
  
  /* Convert an fsmap to an ext4_fsmap. */
  void ext4_fsmap_to_internal(struct super_block *sb, struct ext4_fsmap *dest,
  			    struct fsmap *src)
  {
  	dest->fmr_device = src->fmr_device;
  	dest->fmr_flags = src->fmr_flags;
  	dest->fmr_physical = src->fmr_physical >> sb->s_blocksize_bits;
  	dest->fmr_owner = src->fmr_owner;
  	dest->fmr_length = src->fmr_length >> sb->s_blocksize_bits;
  }
  
  /* getfsmap query state */
  struct ext4_getfsmap_info {
  	struct ext4_fsmap_head	*gfi_head;
  	ext4_fsmap_format_t	gfi_formatter;	/* formatting fn */
  	void			*gfi_format_arg;/* format buffer */
  	ext4_fsblk_t		gfi_next_fsblk;	/* next fsblock we expect */
  	u32			gfi_dev;	/* device id */
  	ext4_group_t		gfi_agno;	/* bg number, if applicable */
  	struct ext4_fsmap	gfi_low;	/* low rmap key */
  	struct ext4_fsmap	gfi_high;	/* high rmap key */
  	struct ext4_fsmap	gfi_lastfree;	/* free ext at end of last bg */
  	struct list_head	gfi_meta_list;	/* fixed metadata list */
  	bool			gfi_last;	/* last extent? */
  };
  
  /* Associate a device with a getfsmap handler. */
  struct ext4_getfsmap_dev {
  	int			(*gfd_fn)(struct super_block *sb,
  				      struct ext4_fsmap *keys,
  				      struct ext4_getfsmap_info *info);
  	u32			gfd_dev;
  };
  
  /* Compare two getfsmap device handlers. */
  static int ext4_getfsmap_dev_compare(const void *p1, const void *p2)
  {
  	const struct ext4_getfsmap_dev *d1 = p1;
  	const struct ext4_getfsmap_dev *d2 = p2;
  
  	return d1->gfd_dev - d2->gfd_dev;
  }
  
  /* Compare a record against our starting point */
  static bool ext4_getfsmap_rec_before_low_key(struct ext4_getfsmap_info *info,
  					     struct ext4_fsmap *rec)
  {
  	return rec->fmr_physical < info->gfi_low.fmr_physical;
  }
  
  /*
   * Format a reverse mapping for getfsmap, having translated rm_startblock
   * into the appropriate daddr units.
   */
  static int ext4_getfsmap_helper(struct super_block *sb,
  				struct ext4_getfsmap_info *info,
  				struct ext4_fsmap *rec)
  {
  	struct ext4_fsmap fmr;
  	struct ext4_sb_info *sbi = EXT4_SB(sb);
  	ext4_fsblk_t rec_fsblk = rec->fmr_physical;
  	ext4_group_t agno;
  	ext4_grpblk_t cno;
  	int error;
  
  	if (fatal_signal_pending(current))
  		return -EINTR;
  
  	/*
  	 * Filter out records that start before our startpoint, if the
  	 * caller requested that.
  	 */
  	if (ext4_getfsmap_rec_before_low_key(info, rec)) {
  		rec_fsblk += rec->fmr_length;
  		if (info->gfi_next_fsblk < rec_fsblk)
  			info->gfi_next_fsblk = rec_fsblk;
  		return EXT4_QUERY_RANGE_CONTINUE;
  	}
  
  	/* Are we just counting mappings? */
  	if (info->gfi_head->fmh_count == 0) {
  		if (info->gfi_head->fmh_entries == UINT_MAX)
  			return EXT4_QUERY_RANGE_ABORT;
  
  		if (rec_fsblk > info->gfi_next_fsblk)
  			info->gfi_head->fmh_entries++;
  
  		if (info->gfi_last)
  			return EXT4_QUERY_RANGE_CONTINUE;
  
  		info->gfi_head->fmh_entries++;
  
  		rec_fsblk += rec->fmr_length;
  		if (info->gfi_next_fsblk < rec_fsblk)
  			info->gfi_next_fsblk = rec_fsblk;
  		return EXT4_QUERY_RANGE_CONTINUE;
  	}
  
  	/*
  	 * If the record starts past the last physical block we saw,
  	 * then we've found a gap.  Report the gap as being owned by
  	 * whatever the caller specified is the missing owner.
  	 */
  	if (rec_fsblk > info->gfi_next_fsblk) {
  		if (info->gfi_head->fmh_entries >= info->gfi_head->fmh_count)
  			return EXT4_QUERY_RANGE_ABORT;
  
  		ext4_get_group_no_and_offset(sb, info->gfi_next_fsblk,
  				&agno, &cno);
  		trace_ext4_fsmap_mapping(sb, info->gfi_dev, agno,
  				EXT4_C2B(sbi, cno),
  				rec_fsblk - info->gfi_next_fsblk,
  				EXT4_FMR_OWN_UNKNOWN);
  
  		fmr.fmr_device = info->gfi_dev;
  		fmr.fmr_physical = info->gfi_next_fsblk;
  		fmr.fmr_owner = EXT4_FMR_OWN_UNKNOWN;
  		fmr.fmr_length = rec_fsblk - info->gfi_next_fsblk;
  		fmr.fmr_flags = FMR_OF_SPECIAL_OWNER;
  		error = info->gfi_formatter(&fmr, info->gfi_format_arg);
  		if (error)
  			return error;
  		info->gfi_head->fmh_entries++;
  	}
  
  	if (info->gfi_last)
  		goto out;
  
  	/* Fill out the extent we found */
  	if (info->gfi_head->fmh_entries >= info->gfi_head->fmh_count)
  		return EXT4_QUERY_RANGE_ABORT;
  
  	ext4_get_group_no_and_offset(sb, rec_fsblk, &agno, &cno);
  	trace_ext4_fsmap_mapping(sb, info->gfi_dev, agno, EXT4_C2B(sbi, cno),
  			rec->fmr_length, rec->fmr_owner);
  
  	fmr.fmr_device = info->gfi_dev;
  	fmr.fmr_physical = rec_fsblk;
  	fmr.fmr_owner = rec->fmr_owner;
  	fmr.fmr_flags = FMR_OF_SPECIAL_OWNER;
  	fmr.fmr_length = rec->fmr_length;
  	error = info->gfi_formatter(&fmr, info->gfi_format_arg);
  	if (error)
  		return error;
  	info->gfi_head->fmh_entries++;
  
  out:
  	rec_fsblk += rec->fmr_length;
  	if (info->gfi_next_fsblk < rec_fsblk)
  		info->gfi_next_fsblk = rec_fsblk;
  	return EXT4_QUERY_RANGE_CONTINUE;
  }
  
  static inline ext4_fsblk_t ext4_fsmap_next_pblk(struct ext4_fsmap *fmr)
  {
  	return fmr->fmr_physical + fmr->fmr_length;
  }
  
  /* Transform a blockgroup's free record into a fsmap */
  static int ext4_getfsmap_datadev_helper(struct super_block *sb,
  					ext4_group_t agno, ext4_grpblk_t start,
  					ext4_grpblk_t len, void *priv)
  {
  	struct ext4_fsmap irec;
  	struct ext4_getfsmap_info *info = priv;
  	struct ext4_fsmap *p;
  	struct ext4_fsmap *tmp;
  	struct ext4_sb_info *sbi = EXT4_SB(sb);
  	ext4_fsblk_t fsb;
  	ext4_fsblk_t fslen;
  	int error;
  
  	fsb = (EXT4_C2B(sbi, start) + ext4_group_first_block_no(sb, agno));
  	fslen = EXT4_C2B(sbi, len);
  
  	/* If the retained free extent record is set... */
  	if (info->gfi_lastfree.fmr_owner) {
  		/* ...and abuts this one, lengthen it and return. */
  		if (ext4_fsmap_next_pblk(&info->gfi_lastfree) == fsb) {
  			info->gfi_lastfree.fmr_length += fslen;
  			return 0;
  		}
  
  		/*
  		 * There's a gap between the two free extents; emit the
  		 * retained extent prior to merging the meta_list.
  		 */
  		error = ext4_getfsmap_helper(sb, info, &info->gfi_lastfree);
  		if (error)
  			return error;
  		info->gfi_lastfree.fmr_owner = 0;
  	}
  
  	/* Merge in any relevant extents from the meta_list */
  	list_for_each_entry_safe(p, tmp, &info->gfi_meta_list, fmr_list) {
  		if (p->fmr_physical + p->fmr_length <= info->gfi_next_fsblk) {
  			list_del(&p->fmr_list);
  			kfree(p);
  		} else if (p->fmr_physical < fsb) {
  			error = ext4_getfsmap_helper(sb, info, p);
  			if (error)
  				return error;
  
  			list_del(&p->fmr_list);
  			kfree(p);
  		}
  	}
  
  	irec.fmr_device = 0;
  	irec.fmr_physical = fsb;
  	irec.fmr_length = fslen;
  	irec.fmr_owner = EXT4_FMR_OWN_FREE;
  	irec.fmr_flags = 0;
  
  	/* If this is a free extent at the end of a bg, buffer it. */
  	if (ext4_fsmap_next_pblk(&irec) ==
  			ext4_group_first_block_no(sb, agno + 1)) {
  		info->gfi_lastfree = irec;
  		return 0;
  	}
  
  	/* Otherwise, emit it */
  	return ext4_getfsmap_helper(sb, info, &irec);
  }
  
  /* Execute a getfsmap query against the log device. */
  static int ext4_getfsmap_logdev(struct super_block *sb, struct ext4_fsmap *keys,
  				struct ext4_getfsmap_info *info)
  {
  	journal_t *journal = EXT4_SB(sb)->s_journal;
  	struct ext4_fsmap irec;
  
  	/* Set up search keys */
  	info->gfi_low = keys[0];
  	info->gfi_low.fmr_length = 0;
  
  	memset(&info->gfi_high, 0xFF, sizeof(info->gfi_high));
  
  	trace_ext4_fsmap_low_key(sb, info->gfi_dev, 0,
  			info->gfi_low.fmr_physical,
  			info->gfi_low.fmr_length,
  			info->gfi_low.fmr_owner);
  
  	trace_ext4_fsmap_high_key(sb, info->gfi_dev, 0,
  			info->gfi_high.fmr_physical,
  			info->gfi_high.fmr_length,
  			info->gfi_high.fmr_owner);
  
  	if (keys[0].fmr_physical > 0)
  		return 0;
  
  	/* Fabricate an rmap entry for the external log device. */
  	irec.fmr_physical = journal->j_blk_offset;
  	irec.fmr_length = journal->j_total_len;
  	irec.fmr_owner = EXT4_FMR_OWN_LOG;
  	irec.fmr_flags = 0;
  
  	return ext4_getfsmap_helper(sb, info, &irec);
  }
  
  /* Helper to fill out an ext4_fsmap. */
  static inline int ext4_getfsmap_fill(struct list_head *meta_list,
  				     ext4_fsblk_t fsb, ext4_fsblk_t len,
  				     uint64_t owner)
  {
  	struct ext4_fsmap *fsm;
  
  	fsm = kmalloc(sizeof(*fsm), GFP_NOFS);
  	if (!fsm)
  		return -ENOMEM;
  	fsm->fmr_device = 0;
  	fsm->fmr_flags = 0;
  	fsm->fmr_physical = fsb;
  	fsm->fmr_owner = owner;
  	fsm->fmr_length = len;
  	list_add_tail(&fsm->fmr_list, meta_list);
  
  	return 0;
  }
  
  /*
   * This function returns the number of file system metadata blocks at
   * the beginning of a block group, including the reserved gdt blocks.
   */
  static unsigned int ext4_getfsmap_find_sb(struct super_block *sb,
  					  ext4_group_t agno,
  					  struct list_head *meta_list)
  {
  	struct ext4_sb_info *sbi = EXT4_SB(sb);
  	ext4_fsblk_t fsb = ext4_group_first_block_no(sb, agno);
  	ext4_fsblk_t len;
  	unsigned long first_meta_bg = le32_to_cpu(sbi->s_es->s_first_meta_bg);
  	unsigned long metagroup = agno / EXT4_DESC_PER_BLOCK(sb);
  	int error;
  
  	/* Record the superblock. */
  	if (ext4_bg_has_super(sb, agno)) {
  		error = ext4_getfsmap_fill(meta_list, fsb, 1, EXT4_FMR_OWN_FS);
  		if (error)
  			return error;
  		fsb++;
  	}
  
  	/* Record the group descriptors. */
  	len = ext4_bg_num_gdb(sb, agno);
  	if (!len)
  		return 0;
  	error = ext4_getfsmap_fill(meta_list, fsb, len,
  				   EXT4_FMR_OWN_GDT);
  	if (error)
  		return error;
  	fsb += len;
  
  	/* Reserved GDT blocks */
  	if (!ext4_has_feature_meta_bg(sb) || metagroup < first_meta_bg) {
  		len = le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
  		error = ext4_getfsmap_fill(meta_list, fsb, len,
  					   EXT4_FMR_OWN_RESV_GDT);
  		if (error)
  			return error;
  	}
  
  	return 0;
  }
  
  /* Compare two fsmap items. */
  static int ext4_getfsmap_compare(void *priv,
  				 const struct list_head *a,
  				 const struct list_head *b)
  {
  	struct ext4_fsmap *fa;
  	struct ext4_fsmap *fb;
  
  	fa = container_of(a, struct ext4_fsmap, fmr_list);
  	fb = container_of(b, struct ext4_fsmap, fmr_list);
  	if (fa->fmr_physical < fb->fmr_physical)
  		return -1;
  	else if (fa->fmr_physical > fb->fmr_physical)
  		return 1;
  	return 0;
  }
  
  /* Merge adjacent extents of fixed metadata. */
  static void ext4_getfsmap_merge_fixed_metadata(struct list_head *meta_list)
  {
  	struct ext4_fsmap *p;
  	struct ext4_fsmap *prev = NULL;
  	struct ext4_fsmap *tmp;
  
  	list_for_each_entry_safe(p, tmp, meta_list, fmr_list) {
  		if (!prev) {
  			prev = p;
  			continue;
  		}
  
  		if (prev->fmr_owner == p->fmr_owner &&
  		    prev->fmr_physical + prev->fmr_length == p->fmr_physical) {
  			prev->fmr_length += p->fmr_length;
  			list_del(&p->fmr_list);
  			kfree(p);
  		} else
  			prev = p;
  	}
  }
  
  /* Free a list of fixed metadata. */
  static void ext4_getfsmap_free_fixed_metadata(struct list_head *meta_list)
  {
  	struct ext4_fsmap *p;
  	struct ext4_fsmap *tmp;
  
  	list_for_each_entry_safe(p, tmp, meta_list, fmr_list) {
  		list_del(&p->fmr_list);
  		kfree(p);
  	}
  }
  
  /* Find all the fixed metadata in the filesystem. */
  static int ext4_getfsmap_find_fixed_metadata(struct super_block *sb,
  					     struct list_head *meta_list)
  {
  	struct ext4_group_desc *gdp;
  	ext4_group_t agno;
  	int error;
  
  	INIT_LIST_HEAD(meta_list);
  
  	/* Collect everything. */
  	for (agno = 0; agno < EXT4_SB(sb)->s_groups_count; agno++) {
  		gdp = ext4_get_group_desc(sb, agno, NULL);
  		if (!gdp) {
  			error = -EFSCORRUPTED;
  			goto err;
  		}
  
  		/* Superblock & GDT */
  		error = ext4_getfsmap_find_sb(sb, agno, meta_list);
  		if (error)
  			goto err;
  
  		/* Block bitmap */
  		error = ext4_getfsmap_fill(meta_list,
  					   ext4_block_bitmap(sb, gdp), 1,
  					   EXT4_FMR_OWN_BLKBM);
  		if (error)
  			goto err;
  
  		/* Inode bitmap */
  		error = ext4_getfsmap_fill(meta_list,
  					   ext4_inode_bitmap(sb, gdp), 1,
  					   EXT4_FMR_OWN_INOBM);
  		if (error)
  			goto err;
  
  		/* Inodes */
  		error = ext4_getfsmap_fill(meta_list,
  					   ext4_inode_table(sb, gdp),
  					   EXT4_SB(sb)->s_itb_per_group,
  					   EXT4_FMR_OWN_INODES);
  		if (error)
  			goto err;
  	}
  
  	/* Sort the list */
  	list_sort(NULL, meta_list, ext4_getfsmap_compare);
  
  	/* Merge adjacent extents */
  	ext4_getfsmap_merge_fixed_metadata(meta_list);
  
  	return 0;
  err:
  	ext4_getfsmap_free_fixed_metadata(meta_list);
  	return error;
  }
  
  /* Execute a getfsmap query against the buddy bitmaps */
  static int ext4_getfsmap_datadev(struct super_block *sb,
  				 struct ext4_fsmap *keys,
  				 struct ext4_getfsmap_info *info)
  {
  	struct ext4_sb_info *sbi = EXT4_SB(sb);
  	ext4_fsblk_t start_fsb;
  	ext4_fsblk_t end_fsb;
  	ext4_fsblk_t bofs;
  	ext4_fsblk_t eofs;
  	ext4_group_t start_ag;
  	ext4_group_t end_ag;
  	ext4_grpblk_t first_cluster;
  	ext4_grpblk_t last_cluster;
  	int error = 0;
  
  	bofs = le32_to_cpu(sbi->s_es->s_first_data_block);
  	eofs = ext4_blocks_count(sbi->s_es);
  	if (keys[0].fmr_physical >= eofs)
  		return 0;
  	else if (keys[0].fmr_physical < bofs)
  		keys[0].fmr_physical = bofs;
  	if (keys[1].fmr_physical >= eofs)
  		keys[1].fmr_physical = eofs - 1;
  	start_fsb = keys[0].fmr_physical;
  	end_fsb = keys[1].fmr_physical;
  
  	/* Determine first and last group to examine based on start and end */
  	ext4_get_group_no_and_offset(sb, start_fsb, &start_ag, &first_cluster);
  	ext4_get_group_no_and_offset(sb, end_fsb, &end_ag, &last_cluster);
  
  	/*
  	 * Convert the fsmap low/high keys to bg based keys.  Initialize
  	 * low to the fsmap low key and max out the high key to the end
  	 * of the bg.
  	 */
  	info->gfi_low = keys[0];
  	info->gfi_low.fmr_physical = EXT4_C2B(sbi, first_cluster);
  	info->gfi_low.fmr_length = 0;
  
  	memset(&info->gfi_high, 0xFF, sizeof(info->gfi_high));
  
  	/* Assemble a list of all the fixed-location metadata. */
  	error = ext4_getfsmap_find_fixed_metadata(sb, &info->gfi_meta_list);
  	if (error)
  		goto err;
  
  	/* Query each bg */
  	for (info->gfi_agno = start_ag;
  	     info->gfi_agno <= end_ag;
  	     info->gfi_agno++) {
  		/*
  		 * Set the bg high key from the fsmap high key if this
  		 * is the last bg that we're querying.
  		 */
  		if (info->gfi_agno == end_ag) {
  			info->gfi_high = keys[1];
  			info->gfi_high.fmr_physical = EXT4_C2B(sbi,
  					last_cluster);
  			info->gfi_high.fmr_length = 0;
  		}
  
  		trace_ext4_fsmap_low_key(sb, info->gfi_dev, info->gfi_agno,
  				info->gfi_low.fmr_physical,
  				info->gfi_low.fmr_length,
  				info->gfi_low.fmr_owner);
  
  		trace_ext4_fsmap_high_key(sb, info->gfi_dev, info->gfi_agno,
  				info->gfi_high.fmr_physical,
  				info->gfi_high.fmr_length,
  				info->gfi_high.fmr_owner);
  
  		error = ext4_mballoc_query_range(sb, info->gfi_agno,
  				EXT4_B2C(sbi, info->gfi_low.fmr_physical),
  				EXT4_B2C(sbi, info->gfi_high.fmr_physical),
  				ext4_getfsmap_datadev_helper, info);
  		if (error)
  			goto err;
  
  		/*
  		 * Set the bg low key to the start of the bg prior to
  		 * moving on to the next bg.
  		 */
  		if (info->gfi_agno == start_ag)
  			memset(&info->gfi_low, 0, sizeof(info->gfi_low));
  	}
  
  	/* Do we have a retained free extent? */
  	if (info->gfi_lastfree.fmr_owner) {
  		error = ext4_getfsmap_helper(sb, info, &info->gfi_lastfree);
  		if (error)
  			goto err;
  	}
  
  	/* Report any gaps at the end of the bg */
  	info->gfi_last = true;
  	error = ext4_getfsmap_datadev_helper(sb, end_ag, last_cluster, 0, info);
  	if (error)
  		goto err;
  
  err:
  	ext4_getfsmap_free_fixed_metadata(&info->gfi_meta_list);
  	return error;
  }
  
  /* Do we recognize the device? */
  static bool ext4_getfsmap_is_valid_device(struct super_block *sb,
  					  struct ext4_fsmap *fm)
  {
  	if (fm->fmr_device == 0 || fm->fmr_device == UINT_MAX ||
  	    fm->fmr_device == new_encode_dev(sb->s_bdev->bd_dev))
  		return true;
  	if (EXT4_SB(sb)->s_journal_bdev &&
  	    fm->fmr_device == new_encode_dev(EXT4_SB(sb)->s_journal_bdev->bd_dev))
  		return true;
  	return false;
  }
  
  /* Ensure that the low key is less than the high key. */
  static bool ext4_getfsmap_check_keys(struct ext4_fsmap *low_key,
  				     struct ext4_fsmap *high_key)
  {
  	if (low_key->fmr_device > high_key->fmr_device)
  		return false;
  	if (low_key->fmr_device < high_key->fmr_device)
  		return true;
  
  	if (low_key->fmr_physical > high_key->fmr_physical)
  		return false;
  	if (low_key->fmr_physical < high_key->fmr_physical)
  		return true;
  
  	if (low_key->fmr_owner > high_key->fmr_owner)
  		return false;
  	if (low_key->fmr_owner < high_key->fmr_owner)
  		return true;
  
  	return false;
  }
  
  #define EXT4_GETFSMAP_DEVS	2
  /*
   * Get filesystem's extents as described in head, and format for
   * output.  Calls formatter to fill the user's buffer until all
   * extents are mapped, until the passed-in head->fmh_count slots have
   * been filled, or until the formatter short-circuits the loop, if it
   * is tracking filled-in extents on its own.
   *
   * Key to Confusion
   * ----------------
   * There are multiple levels of keys and counters at work here:
   * _fsmap_head.fmh_keys		-- low and high fsmap keys passed in;
   * 				   these reflect fs-wide block addrs.
   * dkeys			-- fmh_keys used to query each device;
   * 				   these are fmh_keys but w/ the low key
   * 				   bumped up by fmr_length.
   * _getfsmap_info.gfi_next_fsblk-- next fs block we expect to see; this
   *				   is how we detect gaps in the fsmap
   *				   records and report them.
   * _getfsmap_info.gfi_low/high	-- per-bg low/high keys computed from
   * 				   dkeys; used to query the free space.
   */
  int ext4_getfsmap(struct super_block *sb, struct ext4_fsmap_head *head,
  		  ext4_fsmap_format_t formatter, void *arg)
  {
  	struct ext4_fsmap dkeys[2];	/* per-dev keys */
  	struct ext4_getfsmap_dev handlers[EXT4_GETFSMAP_DEVS];
  	struct ext4_getfsmap_info info = { NULL };
  	int i;
  	int error = 0;
  
  	if (head->fmh_iflags & ~FMH_IF_VALID)
  		return -EINVAL;
  	if (!ext4_getfsmap_is_valid_device(sb, &head->fmh_keys[0]) ||
  	    !ext4_getfsmap_is_valid_device(sb, &head->fmh_keys[1]))
  		return -EINVAL;
  
  	head->fmh_entries = 0;
  
  	/* Set up our device handlers. */
  	memset(handlers, 0, sizeof(handlers));
  	handlers[0].gfd_dev = new_encode_dev(sb->s_bdev->bd_dev);
  	handlers[0].gfd_fn = ext4_getfsmap_datadev;
  	if (EXT4_SB(sb)->s_journal_bdev) {
  		handlers[1].gfd_dev = new_encode_dev(
  				EXT4_SB(sb)->s_journal_bdev->bd_dev);
  		handlers[1].gfd_fn = ext4_getfsmap_logdev;
  	}
  
  	sort(handlers, EXT4_GETFSMAP_DEVS, sizeof(struct ext4_getfsmap_dev),
  			ext4_getfsmap_dev_compare, NULL);
  
  	/*
  	 * To continue where we left off, we allow userspace to use the
  	 * last mapping from a previous call as the low key of the next.
  	 * This is identified by a non-zero length in the low key. We
  	 * have to increment the low key in this scenario to ensure we
  	 * don't return the same mapping again, and instead return the
  	 * very next mapping.
  	 *
  	 * Bump the physical offset as there can be no other mapping for
  	 * the same physical block range.
  	 */
  	dkeys[0] = head->fmh_keys[0];
  	dkeys[0].fmr_physical += dkeys[0].fmr_length;
  	dkeys[0].fmr_owner = 0;
  	dkeys[0].fmr_length = 0;
  	memset(&dkeys[1], 0xFF, sizeof(struct ext4_fsmap));
  
  	if (!ext4_getfsmap_check_keys(dkeys, &head->fmh_keys[1]))
  		return -EINVAL;
  
  	info.gfi_next_fsblk = head->fmh_keys[0].fmr_physical +
  			  head->fmh_keys[0].fmr_length;
  	info.gfi_formatter = formatter;
  	info.gfi_format_arg = arg;
  	info.gfi_head = head;
  
  	/* For each device we support... */
  	for (i = 0; i < EXT4_GETFSMAP_DEVS; i++) {
  		/* Is this device within the range the user asked for? */
  		if (!handlers[i].gfd_fn)
  			continue;
  		if (head->fmh_keys[0].fmr_device > handlers[i].gfd_dev)
  			continue;
  		if (head->fmh_keys[1].fmr_device < handlers[i].gfd_dev)
  			break;
  
  		/*
  		 * If this device number matches the high key, we have
  		 * to pass the high key to the handler to limit the
  		 * query results.  If the device number exceeds the
  		 * low key, zero out the low key so that we get
  		 * everything from the beginning.
  		 */
  		if (handlers[i].gfd_dev == head->fmh_keys[1].fmr_device)
  			dkeys[1] = head->fmh_keys[1];
  		if (handlers[i].gfd_dev > head->fmh_keys[0].fmr_device)
  			memset(&dkeys[0], 0, sizeof(struct ext4_fsmap));
  
  		info.gfi_dev = handlers[i].gfd_dev;
  		info.gfi_last = false;
  		info.gfi_agno = -1;
  		error = handlers[i].gfd_fn(sb, dkeys, &info);
  		if (error)
  			break;
  		info.gfi_next_fsblk = 0;
  	}
  
  	head->fmh_oflags = FMH_OF_DEV_T;
  	return error;
  }
  