'qemu-img snapshot' allows new snapshot to be created with the name of an existing snapshot

qemu-img _may_ be working as designed, but it feels like this could be a bug. I'd certainly prefer to only allow unique snapshot names (unless maybe something like a "--force-non-unique-snapshot-names" was also specified).

If this really is correct behaviour, it should be documented as qemu-img(1) currently specifies no details whatsoever regarding expected behaviour or valid snapshot names.

$ qemu-img snapshot -l image.cow
$ qemu-img snapshot -c foo image.cow
$ qemu-img snapshot -l image.cow
Snapshot list:
ID TAG VM SIZE DATE VM CLOCK
1 foo 0 2014-11-26 08:30:53 00:00:00.000
$ qemu-img snapshot -c foo image.cow
$ qemu-img snapshot -l image.cow
Snapshot list:
ID TAG VM SIZE DATE VM CLOCK
1 foo 0 2014-11-26 08:30:53 00:00:00.000
2 foo 0 2014-11-26 08:30:58 00:00:00.000
$ qemu-img snapshot -c foo image.cow
$ qemu-img snapshot -l image.cow
Snapshot list:
ID TAG VM SIZE DATE VM CLOCK
1 foo 0 2014-11-26 08:30:53 00:00:00.000
2 foo 0 2014-11-26 08:30:58 00:00:00.000
3 foo 0 2014-11-26 08:31:00 00:00:00.000
$ qemu-img snapshot -d foo image.cow
$ qemu-img snapshot -l image.cow
Snapshot list:
ID TAG VM SIZE DATE VM CLOCK
2 foo 0 2014-11-26 08:30:58 00:00:00.000
3 foo 0 2014-11-26 08:31:00 00:00:00.000
$ qemu-img snapshot -d foo image.cow
$ qemu-img snapshot -l image.cow
Snapshot list:
ID TAG VM SIZE DATE VM CLOCK
3 foo 0 2014-11-26 08:31:00 00:00:00.000
$ qemu-img snapshot -d foo image.cow
$ qemu-img snapshot -l image.cow
$

Note also how snapshot deletion works in reverse order - the oldest snapshot with a given name is deleted first.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: qemu-utils 2.1+dfsg-4ubuntu9
ProcVersionSignature: Ubuntu 3.16.0-25.33-generic 3.16.7
Uname: Linux 3.16.0-25-generic x86_64
ApportVersion: 2.14.7-0ubuntu10
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Nov 26 08:28:16 2014
InstallationDate: Installed on 2014-04-11 (228 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Daily amd64 (20140409)
KvmCmdLine:
 COMMAND STAT EUID RUID PID PPID %CPU COMMAND
 kvm-irqfd-clean S< 0 0 719 2 0.0 [kvm-irqfd-clean]
MachineType: LENOVO 20AQCTO1WW
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.16.0-25-generic root=/dev/mapper/ubuntu--vg-root ro quiet splash vt.handoff=7
SourcePackage: qemu
UpgradeStatus: Upgraded to vivid on 2014-05-08 (201 days ago)
dmi.bios.date: 02/10/2014
dmi.bios.vendor: LENOVO
dmi.bios.version: GJET71WW (2.21 )
dmi.board.asset.tag: Not Available
dmi.board.name: 20AQCTO1WW
dmi.board.vendor: LENOVO
dmi.board.version: 0B98405 STD
dmi.chassis.asset.tag: No Asset Information
dmi.chassis.type: 10
dmi.chassis.vendor: LENOVO
dmi.chassis.version: Not Available
dmi.modalias: dmi:bvnLENOVO:bvrGJET71WW(2.21):bd02/10/2014:svnLENOVO:pn20AQCTO1WW:pvrThinkPadT440s:rvnLENOVO:rn20AQCTO1WW:rvr0B98405STD:cvnLENOVO:ct10:cvrNotAvailable:
dmi.product.name: 20AQCTO1WW
dmi.product.version: ThinkPad T440s
dmi.sys.vendor: LENOVO