On Tue, Feb 01 2022, Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > On Tue, 01 Feb 2022 13:39:23 +0100 > Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > >> On Tue, Feb 01 2022, Jason Gunthorpe <jgg@xxxxxxxxxx> wrote: >> >> > On Tue, Feb 01, 2022 at 12:23:05PM +0100, Cornelia Huck wrote: >> >> On Sun, Jan 30 2022, Yishai Hadas <yishaih@xxxxxxxxxx> wrote: >> >> >> >> > From: Jason Gunthorpe <jgg@xxxxxxxxxx> >> >> > >> >> > v1 was never implemented and is replaced by v2. >> >> > >> >> > The old uAPI definitions are removed from the header file. As per Linus's >> >> > past remarks we do not have a hard requirement to retain compilation >> >> > compatibility in uapi headers and qemu is already following Linus's >> >> > preferred model of copying the kernel headers. >> >> >> >> If we are all in agreement that we will replace v1 with v2 (and I think >> >> we are), we probably should remove the x-enable-migration stuff in QEMU >> >> sooner rather than later, to avoid leaving a trap for the next >> >> unsuspecting person trying to update the headers. >> > >> > Once we have agreement on the kernel patch we plan to send a QEMU >> > patch making it support the v2 interface and the migration >> > non-experimental. We are also working to fixing the error paths, at >> > least least within the limitations of the current qemu design. >> >> I'd argue that just ripping out the old interface first would be easier, >> as it does not require us to synchronize with a headers sync (and does >> not require to synchronize a headers sync with ripping it out...) >> >> > The v1 support should remain in old releases as it is being used in >> > the field "experimentally". >> >> Of course; it would be hard to rip it out retroactively :) >> >> But it should really be gone in QEMU 7.0. >> >> Considering adding the v2 uapi, we might get unlucky: The Linux 5.18 >> merge window will likely be in mid-late March (and we cannot run a >> headers sync before the patches hit Linus' tree), while QEMU 7.0 will >> likely enter freeze in mid-late March as well. So there's a non-zero >> chance that the new uapi will need to be deferred to 7.1. > > > Agreed that v1 migration TYPE/SUBTYPE should live in infamy as > reserved, but I'm not sure why we need to make the rest of it a big > complicated problem. On one hand, leaving stubs for the necessary > structure and macros until QEMU gets updated doesn't seem so terrible. > Nor actually does letting the next QEMU header update cause build > breakages, which would probably frustrate the person submitting that > update, but it's not like QEMU hasn't done selective header updates in > the past. The former is probably the more friendly approach if we > don't outrage someone in the kernel community in the meantime. Leaving stubs in (while making it clear that v1 is not something you should use) seems like a good compromise. While we have done selective headers updates in QEMU in the past, I always found them painful, so I'd like to avoid that.
