result-output.txt

+ rm -rf testimage testmount
+ mkdir testmount
+ fallocate -l 1G testimage
+ mkfs.ext4 testimage
mke2fs 1.45.6 (20-Mar-2020)
Discarding device blocks:   4096/262144             done                            
Creating filesystem with 262144 4k blocks and 65536 inodes
Filesystem UUID: f4746471-fb36-4a46-8b05-258557c24a0c
Superblock backups stored on blocks: 
	32768, 98304, 163840, 229376

Allocating group tables: 0/8   done                            
Writing inode tables: 0/8   done                            
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: 0/8   done

+ mount testimage testmount
+ trap cleanup ERR
+ trap cleanup EXIT
+ fallocate -l 200M testmount/test1
+ fallocate -l 200M testmount/test2
+ fallocate -l 200M testmount/test3
+ fallocate -l 200M testmount/test4
+ fallocate -l 205M testmount/test1
+ fallocate -l 205M testmount/test2
+ fallocate -l 205M testmount/test3
+ fallocate -l 205M testmount/test4
+ sync testmount/lost+found testmount/test1 testmount/test2 testmount/test3 testmount/test4 testmount
+ df testmount
Filesystem     1K-blocks   Used Available Use% Mounted on
/dev/loop0        999320 842244     88264  91% /home/farseerfc/tmp/testbtrfsconvert/testmount
+ umount testmount
+ btrfs-convert testimage
create btrfs filesystem:
	blocksize: 4096
	nodesize:  16384
	features:  extref, skinny-metadata (default)
	checksum:  crc32c
creating ext2 image file
creating btrfs metadata
copy inodes [o] [         0/        15]
conversion complete
+ mount testimage testmount
mount: /home/farseerfc/tmp/testbtrfsconvert/testmount: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error.
++ cleanup
++ umount testmount
umount: testmount: not mounted.
+ dmesg
+ tail -n10
[108720.796804] audit: type=1110 audit(1592986026.992:1462): pid=1223346 uid=0 auid=1000 ses=2 msg='op=PAM:setcred grantors=pam_unix,pam_permit,pam_env acct="root" exe="/usr/bin/sudo" hostname=? addr=? terminal=/dev/pts/5 res=success'
[108720.797047] audit: type=1105 audit(1592986026.992:1463): pid=1223346 uid=0 auid=1000 ses=2 msg='op=PAM:session_open grantors=pam_limits,pam_unix,pam_permit acct="root" exe="/usr/bin/sudo" hostname=? addr=? terminal=/dev/pts/5 res=success'
[108721.091932] EXT4-fs (loop0): mounted filesystem with ordered data mode. Opts: (null)
[108724.885590] BTRFS: device fsid 8c731320-4aed-40de-bdd7-c817217625dc devid 1 transid 5 /dev/loop0 scanned by systemd-udevd (1223354)
[108724.887288] BTRFS info (device loop0): disk space caching is enabled
[108724.887292] BTRFS info (device loop0): has skinny extents
[108724.887295] BTRFS info (device loop0): flagging fs with big metadata feature
[108724.891277] BTRFS error (device loop0): dev extent devid 1 physical offset 993198080 len 85786624 is beyond device boundary 1073741824
[108724.891279] BTRFS error (device loop0): failed to verify dev extents against chunks: -117
[108724.919813] BTRFS error (device loop0): open_ctree failed
+ btrfs inspect-internal dump-tree -t CHUNK testimage
btrfs-progs v5.6.1 
chunk tree
leaf 33619968 items 14 free space 14795 generation 3 owner CHUNK_TREE
leaf 33619968 flags 0x1(WRITTEN) backref revision 1
fs uuid 8c731320-4aed-40de-bdd7-c817217625dc
chunk uuid a5a0638e-944a-4b92-989c-8cd252e427e8
	item 0 key (DEV_ITEMS DEV_ITEM 1) itemoff 16185 itemsize 98
		devid 1 total_bytes 1073741824 bytes_used 1023410176
		io_align 4096 io_width 4096 sector_size 4096 type 0
		generation 0 start_offset 0 dev_group 0
		seek_speed 0 bandwidth 0
		uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
		fsid 8c731320-4aed-40de-bdd7-c817217625dc
	item 1 key (FIRST_CHUNK_TREE CHUNK_ITEM 1048576) itemoff 16105 itemsize 80
		length 32505856 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 1048576
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 2 key (FIRST_CHUNK_TREE CHUNK_ITEM 33619968) itemoff 16025 itemsize 80
		length 4194304 owner 2 stripe_len 65536 type SYSTEM
		io_align 4096 io_width 4096 sector_size 4096
		num_stripes 1 sub_stripes 0
			stripe 0 devid 1 offset 33619968
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 3 key (FIRST_CHUNK_TREE CHUNK_ITEM 67174400) itemoff 15945 itemsize 80
		length 33554432 owner 2 stripe_len 65536 type METADATA
		io_align 4096 io_width 4096 sector_size 4096
		num_stripes 1 sub_stripes 0
			stripe 0 devid 1 offset 67174400
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 4 key (FIRST_CHUNK_TREE CHUNK_ITEM 134217728) itemoff 15865 itemsize 80
		length 107372544 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 134217728
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 5 key (FIRST_CHUNK_TREE CHUNK_ITEM 241590272) itemoff 15785 itemsize 80
		length 107372544 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 241590272
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 6 key (FIRST_CHUNK_TREE CHUNK_ITEM 348962816) itemoff 15705 itemsize 80
		length 107372544 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 348962816
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 7 key (FIRST_CHUNK_TREE CHUNK_ITEM 456335360) itemoff 15625 itemsize 80
		length 107372544 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 456335360
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 8 key (FIRST_CHUNK_TREE CHUNK_ITEM 563707904) itemoff 15545 itemsize 80
		length 107372544 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 563707904
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 9 key (FIRST_CHUNK_TREE CHUNK_ITEM 671080448) itemoff 15465 itemsize 80
		length 107372544 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 671080448
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 10 key (FIRST_CHUNK_TREE CHUNK_ITEM 778452992) itemoff 15385 itemsize 80
		length 107372544 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 778452992
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 11 key (FIRST_CHUNK_TREE CHUNK_ITEM 885825536) itemoff 15305 itemsize 80
		length 107372544 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 885825536
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 12 key (FIRST_CHUNK_TREE CHUNK_ITEM 993198080) itemoff 15225 itemsize 80
		length 85786624 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 993198080
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
	item 13 key (FIRST_CHUNK_TREE CHUNK_ITEM 1078984704) itemoff 15145 itemsize 80
		length 8388608 owner 2 stripe_len 65536 type DATA
		io_align 65536 io_width 65536 sector_size 4096
		num_stripes 1 sub_stripes 1
			stripe 0 devid 1 offset 37814272
			dev_uuid 6d4bcef2-cb79-4fe3-a63a-bb0fd07dea30
+ cleanup
+ umount testmount
umount: testmount: not mounted.
++ cleanup
++ umount testmount
umount: testmount: not mounted.

test-btrfs-convert.sh

#!/bin/sh
set -x

cleanup(){
  umount testmount
}

# remove test image and recreate it
rm -rf testimage testmount
mkdir testmount
fallocate -l 1G testimage
mkfs.ext4 testimage

mount testimage testmount
trap cleanup ERR
trap cleanup EXIT

fallocate -l 200M testmount/test1
fallocate -l 200M testmount/test2
fallocate -l 200M testmount/test3
fallocate -l 200M testmount/test4

fallocate -l 205M testmount/test1
fallocate -l 205M testmount/test2
fallocate -l 205M testmount/test3
fallocate -l 205M testmount/test4

sync testmount/* testmount

df testmount
# should remain some space for btrfs-convert to write metadata
umount testmount

btrfs-convert testimage
mount testimage testmount
dmesg | tail -n10
btrfs inspect-internal dump-tree -t CHUNK testimage