qemu-img conversion to qcow2 hangs with blank image less than 100kiB

[Neil Wilson]

If you try to convert a blank image to qcow2 that is less than 100kiB in size then qemu-img hangs trying to seek to the end of the file.

$ truncate --size 102399 /tmp/temp
$ qemu-img convert -p -O qcow2 /tmp/temp /tmp/temp2.qcow2

I'm finding this on all versions of qemu-img v2.

strace shows a seek loop.

ioctl(6, FS_IOC_FIEMAP, 0xb5e68dc4) = 0
_llseek(6, 0, [100000], SEEK_END) = 0
ioctl(6, FS_IOC_FIEMAP, 0xb5e68dc4) = 0
_llseek(6, 0, [100000], SEEK_END) = 0
ioctl(6, FS_IOC_FIEMAP, 0xb5e68dc4) = 0
_llseek(6, 0, [100000], SEEK_END) = 0
ioctl(6, FS_IOC_FIEMAP, 0xb5e68dc4) = 0
_llseek(6, 0, [100000], SEEK_END) = 0
ioctl(6, FS_IOC_FIEMAP, 0xb5e68dc4) = 0
_llseek(6, 0, [100000], SEEK_END) = 0
ioctl(6, FS_IOC_FIEMAP, 0xb5e68dc4) = 0
_llseek(6, 0, [100000], SEEK_END) = 0
ioctl(6, FS_IOC_FIEMAP, 0xb5e68dc4) = 0
_llseek(6, 0, [100000], SEEK_END) = 0
ioctl(6, FS_IOC_FIEMAP, 0xb5e68dc4) = 0
_llseek(6, 0, [100000], SEEK_END) = 0

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: qemu-utils 2.0.0+dfsg-2ubuntu1.10
ProcVersionSignature: User Name 3.13.0-43.72-generic 3.13.11.11
Uname: Linux 3.13.0-43-generic i686
ApportVersion: 2.14.1-0ubuntu3.6
Architecture: i386
Date: Tue Jan 13 14:30:39 2015
SourcePackage: qemu
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Neil Wilson (neil-aldur)]

Workaround is to 'fallocate'. Problem seems to be linked to files with sparse holes in them.

[Scott Moser (smoser)]

verified this fails as described on vivid:
$ dpkg-query --show qemu-utils
qemu-utils 1:2.1+dfsg-11ubuntu1

and also on trusty.

$ dpkg-query --show qemu-utils
qemu-utils 2.0.0+dfsg-2ubuntu1.10

[Serge Hallyn (serge-hallyn)]

Does it also fail with the qemu from
https://launchpad.net/~ubuntu-virt/+archive/ubuntu/virt-daily-upstream ?
(This isn't quite git head, but it is qemu v2.2)

[Serge Hallyn (serge-hallyn)]

Went ahead and tested - it is in fact fixed in the v2.2 version.

[Robie Basak (racb)]

qemu is 2.5 in 16.04 and 2.6.1 in Zesty, so this is presumably Fix Released now. If incorrect, please explain and reopen.