Issue
I want to build a time consuming package (mediapipe) on my Raspberry-Pi buster image under QEMU. So far, I've gotten the image to load and run (including with network connectivity); however, I'm limited to 256MB of storage, which just isn't enough to do much - especially build a mediapipe. Can someone explain why Raspbian images running under QEMU seem to be limited to 256MB?
I've seen some posts about people running with 512MB and even one with 1GB, but they don't seem to be very successful. Can anyone explain the reason for the restriction, and a potential fix?
Solution
The problem here is that a lot of people claim to be running "raspberry pi emulation in QEMU" when they're actually just running Raspbian userspace on top of a kernel for a different machine emulation. So it's easy to be confused if you look at several different tutorials that are really describing entirely different emulation setups. Look for what machine type they pass QEMU.
The "versatilepb" machine type gets used in a lot of tutorials, especially older ones, because it has been in QEMU a long time and it is possible to get it to work with the 1176 CPU that the classic Raspberry Pi boards used. This specific machine has a 256MB maximum memory size, because the real hardware it's emulating has that restriction (it's imposed by the way the physical memory address space is designed). This machine type will never be able to support more RAM, so if you need more then you should ignore any tutorial or setup that uses it.
More recent versions of QEMU really do emulate the actual raspberry pi hardware; these are the raspi0, raspi1ap, raspi2b, raspi3ap, raspi3b machine types. These will have the same amount of RAM as the real raspi hardware they're emulating (either 512MB or 1GB). The downside of these board models is that some of the device emulation is lacking features -- so older QEMU will often not correctly boot a newer kernel, and sometimes devices you would like to use are not present. Also, because the raspi boards hang their ethernet device off the USB controller, the only way to get ethernet on these QEMU models would also be to use a USB ethernet device, eg with:
-device usb-net,netdev=eth0 -netdev user,id=eth0
This probably needs a recent QEMU version to get a working USB controller.
I don't know if there are any tutorials/recipes for running Raspbian on top of the QEMU "virt" board. If there are, this would probably be the best experience, because the virt board permits lots of memory, PCI devices, virtio devices, and is well maintained.
Answered By - Peter Maydell Answer Checked By - Marilyn (WPSolving Volunteer)
