On 2017-01-16 15:18, Stefan Hajnoczi wrote: > On Mon, Jan 16, 2017 at 09:36:51AM +0100, Jan Kiszka wrote: >> some of you may know that we are using a shared memory device similar to >> ivshmem in the partitioning hypervisor Jailhouse [1]. >> >> We started as being compatible to the original ivshmem that QEMU >> implements, but we quickly deviated in some details, and in the recent >> months even more. Some of the deviations are related to making the >> implementation simpler. The new ivshmem takes <500 LoC - Jailhouse is >> aiming at safety critical systems and, therefore, a small code base. >> Other changes address deficits in the original design, like missing >> life-cycle management. > > My first thought is "what about virtio?". Can you share some background > on why ivshmem fits the use case better than virtio? > > The reason I ask is because the ivshmem devices you define would have > parallels to existing virtio devices and this could lead to duplication.
virtio was created as an interface between a host and a guest. It has no notion of direct (or even symmetric) connection between guests. With ivshmem, we want to establish only a minimal host-guest interface. We want to keep the host out of the business negotiating protocol details between two connected guests. So, the trade-off was between reusing existing virtio drivers - in the best case, some changes would have been required definitely - and requiring complex translation of virtio into a vm-to-vm model on the one side and establishing a new driver ecosystem on much simpler host services (500 LoC...). We went for the latter. Jan -- Siemens AG, Corporate Technology, CT RDA ITP SES-DE Corporate Competence Center Embedded Linux
