Xen Network I/O Architecture
TX 방식
[DomU]
1. DomU creates a grant reference providing access to a page
2. DomU forwards the reference as part of the I/O buffer descriptor
3. Invoke a hypervall
[Dom0=driver domain]
1. map the guest page into its address space before sending the request through bridge
2. physical device send the packet
3. device driver frees the pages a callback function is automatically invoked to return a response to netfront which then revokes the grant
RX 방식
[DomU]
1. netfront posts I/O buffer page grants to the RX I/O channel
[Dom0]
1. netback receives a packet from the bridge
2. it receives a posted grant from the I/O channel
3. issues a grant copy hypercall to copy the packet to the guest page
4. netback sends a response to the guest via the RX channel indicating a packet is available
reference
Bridging the Gap between Software and Hardware Techniques for I/O virtualization
[usenix 08] Bridging the Gap between software and hardware techniques for IO virtualization.pdf