Emulating a Raspberry Pi in QEMU: How to increase disk space

[annoybot]

Thanks for writing up your how you got the Raspberry Pi Os to run in Docker

Is there any way to increase the size of the root filesystem? It's got 600Mb free right now, and I need more space for the task I'm working on.

You already seem to be increasing it to 8Gb, but it's not translating to more space for the mounted filesystem. Any suggestions would be welcome.