[Bug 1410288] [NEW] qemu-img conversion to qcow2 hangs with blank image less than 100kiB

[Neil Wilson]

Public bug reported:

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)

** Affects: qemu (Ubuntu)
     Importance: Undecided
         Status: Confirmed


** Tags: apport-bug i386 trusty uec-images

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

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