`Resource temporarily unavailable` when copying large files over 9pfs

[obbardc]

Copying large files over a 9pfs filesystem results in an error Resource temporarily unavailable:

$ fakemachine -v $(pwd):/recipes
Running /bin/bash using kvm backend
bash-5.2# dd if=/dev/zero of=/recipes/test.img bs=100M count=10
dd: error writing '/recipes/test.img': Resource temporarily unavailable
6+0 records in
5+0 records out
574423040 bytes (574 MB, 548 MiB) copied, 2.06091 s, 279 MB/s

This is with both qemu-system-x86 versions 1:8.2.4+ds-1 and 1:9.0.0~rc2+ds-1, along with linux version 6.8.9 from Debian archive.

The versions from bookworm in the docker container seem to work fine.

[obbardc]

Seems to be related to kernel version. Running fakemachine manually with kernel image /boot/vmlinuz-6.7.9-amd64 returns no error (with both qemu versions). I will try to reproduce against mainline kernel & attempt to see which commit broke things!