data loss when flattening a cloned image on giant

[wuxingyi <wuxingyigfs@xxxxxxxxxxx>]

hello, guys,

    I found data lost when flattening a cloned image on giant(0.87.2). The problem can be easily reproduced by runing the following script:

ceph osd pool create wuxingyi 1 1

rbd create --image-format 2 wuxingyi/disk1.img --size 8

#writing "FOOBAR" at offset 0

python writetooffset.py disk1.img 0 FOOBAR

rbd snap create wuxingyi/disk1.img@SNAPSHOT

rbd snap protect wuxingyi/disk1.img@SNAPSHOT

echo "start cloing"

rbd clone wuxingyi/disk1.img@SNAPSHOT wuxingyi/CLONEIMAGE

#writing "WUXINGYI" at offset 4M  of cloned image

python writetooffset.py CLONEIMAGE $((4*1048576)) WUXINGYI

rbd snap create wuxingyi/CLONEIMAGE@CLONEDSNAPSHOT

#modify  at offset 4M  of cloned image

python writetooffset.py CLONEIMAGE $((4*1048576)) HEHEHEHE

echo "start flattening CLONEIMAGE"

rbd flatten wuxingyi/CLONEIMAGE

echo "before rollback"

rbd export wuxingyi/CLONEIMAGE &&  hexdump -C CLONEIMAGE

rm CLONEIMAGE -f

rbd snap rollback wuxingyi/CLONEIMAGE@CLONEDSNAPSHOT

echo "after rollback"

rbd export wuxingyi/CLONEIMAGE &&  hexdump -C CLONEIMAGE

rm CLONEIMAGE -f

where writetooffset.py is a simple python script writing specific data to the specific offset of the image:

#!/usr/bin/python

#coding=utf-8

import sys

import rbd

import rados

cluster = rados.Rados(conffile='/etc/ceph/ceph.conf')

cluster.connect()

ioctx = cluster.open_ioctx('wuxingyi')

rbd_inst = rbd.RBD()

image=rbd.Image(ioctx, sys.argv[1])

image.write(sys.argv[3], int(sys.argv[2]))

The output is something like:

before rollback

Exporting image: 100% complete...done.

00000000  46 4f 4f 42 41 52 00 00  00 00 00 00 00 00 00 00  |FOOBAR..........|

00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|

*

00400000  48 45 48 45 48 45 48 45  00 00 00 00 00 00 00 00  |HEHEHEHE........|

00400010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|

*

00800000

Rolling back to snapshot: 100% complete...done.

after rollback

Exporting image: 100% complete...done.

00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|

*

00400000  57 55 58 49 4e 47 59 49  00 00 00 00 00 00 00 00  |WUXINGYI........|

00400010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|

*

00800000

We can easily fount that the first object of the image is definitely lost, and I found the data loss is happened when flattening, there is only a "head" version of the first object, actually a "snapid" version of the object should also be created and writed when flattening.

But when running this scripts on upstream code, I cannot hit this problem. I look through the upstream code but could not find which commit fixes this bug. I also found the whole state machine dealing with RBD layering changed a lot since giant release.

Could you please give me some hints on which commits should I backport?

Thanks~~~~

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