[Qemu-devel] Question about mmap from user space and accessing emulated device bar0 contents

[Anjali Kulkarni]

Hi,

I am not sure if this is the right forum for my questions -
I am using Qemu+KVM on centOS to run my freebsd based virtual OS. The Qemu
emulates one of my nics - yukon -II 88E8022 chip. Now, my yukon driver
exists in kernel as well as user space(and I will use the one which I want
based on some configs). The kernel driver is able to read the bar0 from PCI
config and also read contents correctly. The user space driver gets the bar0
correctly, and mmaps it into it's process space, but when it reads contents
of bar0, it gets all 0s. This same code when written on a real device works.
Is it due to the fact Qemu is running my freebsd based OS in userland, so
does mmap require some tweaks?
Are there any documents which I could regarding how the Qemu/KVM traps the
read write to bar0 so that it can emulate the device reads/writes?
If this is not the right forum, can you point me to the right one?

Thanks
Anjali