Richard W.M. Jones
2021-Jul-24 10:30 UTC
[Libguestfs] nbdkit: cow.c:591: cow_extents: Assertion `count > 0' failed.
On Sat, Jul 24, 2021 at 11:17:43AM +0100, Richard W.M. Jones wrote:> Just noting this because I don't have time to look into it at the > moment. I suspect (but don't have any evidence for) that this might > be an issue in the cacheextents filter.I was wrong about cacheextents. Here's the simplest reproducer I can come up with: $ ./nbdkit curl https://download.fedoraproject.org/pub/fedora/linux/releases/34/Cloud/x86_64/images/Fedora-Cloud-Base-34-1.2.x86_64.raw.xz --filter=cow --filter=xz --run 'nbdinfo --map $uri' nbdkit: cow.c:591: cow_extents: Assertion `count > 0' failed. It also happens if I download that cloud image and use the file plugin: $ ./nbdkit file Fedora-Cloud-Base-34-1.2.x86_64.raw.xz --filter=cow --filter=xz --run 'nbdinfo --map $uri' nbdkit: cow.c:591: cow_extents: Assertion `count > 0' failed. Weird that we've not seen this before ... Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/
Richard W.M. Jones
2021-Jul-24 10:40 UTC
[Libguestfs] nbdkit: cow.c:591: cow_extents: Assertion `count > 0' failed.
I wonder if this is an overflow: $ ./nbdkit sparse-random 3G --filter=cow --run 'nbdinfo --map $uri' # OK $ ./nbdkit sparse-random 4G --filter=cow --run 'nbdinfo --map $uri' nbdkit: cow.c:591: cow_extents: Assertion `count > 0' failed. Any size >= 4G seems to cause the crash. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-p2v converts physical machines to virtual machines. Boot with a live CD or over the network (PXE) and turn machines into KVM guests. http://libguestfs.org/virt-v2v