[Qemu-discuss] About the host page cache inside the qemu

[Yaodong Yang]

Hi all,

I read the slides "An Update Overview of the QEMU Storage Stack", which 
indicate that if caching mode=none, the host page cache is off and guest disk 
write cache is on. My question is where the implementation is inside the qemu. 
How to control the io to a virtual disk image( a raw disk on top of the ext4 in 
the host filesysytem) 

My understanding is the ios from qemu are sent to the host linux system call, 
the virtual disk is basically a normal file in the host filesystem, how the 
qemu can perform the ios to this file bypassing the host page cache.

Thanks a lot!

Yaodong