ext4: support GETFSMAP ioctls

obj-$(CONFIG_EXT4_FS) += ext4.o

ext4-y	:= balloc.o bitmap.o dir.o file.o fsync.o ialloc.o inode.o page-io.o \

		ioctl.o namei.o super.o symlink.o hash.o resize.o extents.o \

		ext4_jbd2.o migrate.o mballoc.o block_validity.o move_extent.o \

		mmp.o indirect.o extents_status.o xattr.o xattr_user.o \

		xattr_trusted.o inline.o readpage.o sysfs.o

ext4-y	:= balloc.o bitmap.o block_validity.o dir.o ext4_jbd2.o extents.o \

		extents_status.o file.o fsmap.o fsync.o hash.o ialloc.o \

		indirect.o inline.o inode.o ioctl.o mballoc.o migrate.o \

		mmp.o move_extent.o namei.o page-io.o readpage.o resize.o \

		super.o symlink.o sysfs.o xattr.o xattr_trusted.o xattr_user.o

ext4-$(CONFIG_EXT4_FS_POSIX_ACL)	+= acl.o

ext4-$(CONFIG_EXT4_FS_SECURITY)		+= xattr_security.o

/*

 * Copyright (C) 2017 Oracle.  All Rights Reserved.

 *

 * Author: Darrick J. Wong <darrick.wong@oracle.com>

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 *

 * This program is distributed in the hope that it would be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write the Free Software Foundation,

 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301, USA.

 */

#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 (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_maxlen;

	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,

				 struct list_head *a,

				 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. */

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 eofs;

	ext4_group_t start_ag;

	ext4_group_t end_ag;

	ext4_grpblk_t first_cluster;

	ext4_grpblk_t last_cluster;

	int error = 0;

	eofs = ext4_blocks_count(sbi->s_es);

	if (keys[0].fmr_physical >= eofs)

		return 0;

	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)->journal_bdev &&

	    fm->fmr_device == new_encode_dev(EXT4_SB(sb)->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 = {0};

	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)->journal_bdev) {

		handlers[1].gfd_dev = new_encode_dev(

				EXT4_SB(sb)->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));