Hi MST, We are trying to develop a long term fix to the following issue with vhost-user-scsi:
When a live migration starts, Qemu sends a SET_VRING_ADDR message to update the VQ's flags (turning log on). We can't distinguish that message from the first SET_VRING_ADDR message sent after a device reset (given that vhost-user backends are not notified about resets). That distinction is important because we need to know whether to refetch the used ring from guest memory. A while back we sent a patch [1] (which we still use internally) to introduce a message which tells vhost-user backends about device resets. No one ever responded to that patch. They are getting clunky to maintain and we would prefer to converge on a solution which is inline with upstream. [1] https://lists.gnu.org/archive/html/qemu-devel/2018-03/msg05077.html Vhost seems to support the concept of a reset through the reset_device callback in the VhostOps struct. Currently, the vhost-user VhostOps reset callback sends RESET_OWNER message. The docs currently state, though, that this message is obsolete. Looking at the history, I see change d1f8b30ec8dde0318fd1b98d24a64926feae9625 actually changed the message name to RESET_DEVICE, although it was subsequently changed back to RESET_OWNER. With this in mind, we think the code should be improved by: 1) Stopping qemu from sending the RESET_OWNER message on the vhost-user device_reset callback. 2) Amending the docs to better align with the code. 3) If you agree with 1), adding a separate DEVICE_RESET message. If you agree with 1) and 3) would you reconsider patch [1]? If so, I will have to update the patch because the message/features numbers are now taken. Should I update the patch and resend? If you don't plan on stopping Qemu from sending RESET_OWNER, I'd like to post a patch allowing vhost-user-scsi benefit from the RESET_OWNER message (as it currently don't offer a device reset callback). Thanks, Raphael
