Bug 1877209

This bug is blocking us from fixing bug 1861667.
If 'qemu-img --merge' cannot work on bitmap merge from top volume to base volume
we cannot merge bitmaps on merging external snapshot with bitmaps manually.

Tested it with qemu-5.1, also hit this issue.


Versions:
kernel-4.18.0-234.el8.x86_64
qemu-kvm-5.1.0-5.module+el8.3.0+7975+b80d25f1


Steps:
1. create an image and snapshot
# qemu-img create -f qcow2 base.qcow2 1024M
# qemu-img create -f qcow2 -b base.qcow2 top.qcow2

2. add bitmaps
# qemu-img bitmap --add --enable base.qcow2 base_bitmap
# qemu-img bitmap --add --enable top.qcow2 top_bitmap

3. merge bitmap
# qemu-img bitmap -f qcow2 base.qcow2 -F qcow2 -b top.qcow2  --merge top_bitmap base_bitmap
qemu-img: Could not open 'top.qcow2': Could not open backing file: Failed to get shared "write" lock
Is another process using the image [base.qcow2]?



Hi Eric,

Please help check if the scenario has been supported already and if the usage is correct?

According to commit 3b51ab4bf0f49a01cc2db7b954e0669e081719b5, it should be supported in qemu-5.1. I'm not sure if rhel.8.2.1-av support it?


And I have confirmed with aliang, it works well when merging external bitmaps with QMP commands. Many thanks.

Patch posted upstream already: https://lists.nongnu.org/archive/html/qemu-devel/2020-09/msg03412.html

Please let us know if an 8.2.1.z-stream will also be requested or if 8.3.0 will be sufficient.

Upstream patch posted:
https://lists.gnu.org/archive/html/qemu-devel/2020-09/msg03412.html

(In reply to John Ferlan from comment #3)
> Patch posted upstream already:
> https://lists.nongnu.org/archive/html/qemu-devel/2020-09/msg03412.html
> 
> Please let us know if an 8.2.1.z-stream will also be requested or if 8.3.0
> will be sufficient.

Code depending on this will be released in RHV 4.4.3, requiring RHEL 8.3.0,
so I don't think we need a backport for 8.2.1. But having this in 8.3.0 will
be nice.

This is required when libvirt will switch incremental backup to fully
supported status.

v2: https://lists.nongnu.org/archive/html/qemu-devel/2020-09/msg05048.html

(In reply to Xueqiang Wei from comment #2)
> Tested it with qemu-5.1, also hit this issue.
> 
> 
> Versions:
> kernel-4.18.0-234.el8.x86_64
> qemu-kvm-5.1.0-5.module+el8.3.0+7975+b80d25f1

This build lacks the backport, hence...

> 
> 
> Steps:
> 1. create an image and snapshot
> # qemu-img create -f qcow2 base.qcow2 1024M
> # qemu-img create -f qcow2 -b base.qcow2 top.qcow2
> 
> 2. add bitmaps
> # qemu-img bitmap --add --enable base.qcow2 base_bitmap
> # qemu-img bitmap --add --enable top.qcow2 top_bitmap
> 
> 3. merge bitmap
> # qemu-img bitmap -f qcow2 base.qcow2 -F qcow2 -b top.qcow2  --merge
> top_bitmap base_bitmap
> qemu-img: Could not open 'top.qcow2': Could not open backing file: Failed to
> get shared "write" lock
> Is another process using the image [base.qcow2]?

...this failure indeed correctly demonstrates the bug.  With the patch in, the merge will succeed.

> 
> Hi Eric,
> 
> Please help check if the scenario has been supported already and if the
> usage is correct?
> 
> According to commit 3b51ab4bf0f49a01cc2db7b954e0669e081719b5, it should be
> supported in qemu-5.1. I'm not sure if rhel.8.2.1-av support it?

The patch did not make it into qemu-5.1; it is being backported for 8.3.0.

> 
> 
> And I have confirmed with aliang, it works well when merging external
> bitmaps with QMP commands. Many thanks.

Tested with qemu-kvm-5.1.0-10.module+el8.3.0+8254+568ca30d, not hit this issue.
And tested with --add, --remove, --clear, --enable and --disable, also not hit new issue. So set status to VERIFIED.



Versions:
kernel-4.18.0-240.el8.x86_64
qemu-kvm-5.1.0-10.module+el8.3.0+8254+568ca30d


Steps:
1. create an image and snapshot
# qemu-img create -f qcow2 base.qcow2 1024M
# qemu-img create -f qcow2 -F qcow2 -b base.qcow2 top.qcow2

2. add bitmaps
# qemu-img bitmap --add --enable base.qcow2 base_bitmap
# qemu-img bitmap --add --enable top.qcow2 top_bitmap

3. merge bitmap
# qemu-img bitmap -f qcow2 base.qcow2 -F qcow2 -b top.qcow2  --merge top_bitmap base_bitmap
# echo $?
0

# qemu-img info base.qcow2 
image: base.qcow2
file format: qcow2
virtual size: 1 GiB (1073741824 bytes)
disk size: 452 KiB
cluster_size: 65536
Format specific information:
    compat: 1.1
    compression type: zlib
    lazy refcounts: false
    bitmaps:
        [0]:
            flags:
                [0]: auto
            name: base_bitmap
            granularity: 65536
    refcount bits: 16
    corrupt: false

# qemu-img info top.qcow2
image: top.qcow2
file format: qcow2
virtual size: 1 GiB (1073741824 bytes)
disk size: 324 KiB
cluster_size: 65536
backing file: base.qcow2
backing file format: qcow2
Format specific information:
    compat: 1.1
    compression type: zlib
    lazy refcounts: false
    bitmaps:
        [0]:
            flags:
                [0]: auto
            name: top_bitmap
            granularity: 65536
    refcount bits: 16
    corrupt: false

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory (virt:8.3 bug fix and enhancement update), and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2020:5137