[Libguestfs] nbdkit: cow.c:591: cow_extents: Assertion `count > 0' failed.

[Richard W.M. Jones]

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.

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