Re: [PATCH v2 1/2] qemu_capabilities: Introduce QEMU_CAPS_X_USE_CANONICAL_PATH_FOR_RAMBLOCK_ID

On Thu, Jan 14, 2021 at 13:52:45 +0100, Peter Krempa wrote: > On Thu, Jan 14, 2021 at 13:37:23 +0100, Michal Privoznik wrote: >> This capability tracks whether memory-backend-file has >> "x-use-canonical-path-for-ramblock-id" attribute. Introduced into >> QEMU by commit fa0cb34d2210cc749b9a70db99bb41c56ad20831. While >> "x-" prefix is considered experimental or internal to QEMU, the >> next commit justifies its use. > > Since the detection of this feature is not limited to existing qemus, my > requirement that qemu must add acknowledgement that > "x-use-canonical-path-for-ramblock-id" will be treated as a stable > feature from now on and the qemu commit adding that must be mentioned in > this commit.

> > The only other way is to limit the feature detection to any released > qemu (thus qemu-5.2 and previous), since we still will not get a > guarantee that they will not change the flag in the future. Let me reiterate the options when this will be acceptable so that we are in the clear: 1) qemu declares "x-use-canonical-path-for-ramblock-id" stable in code and docs (please cc me on the commit)

2) qemu drops the "x-", and ... 2a) we use "use-canonical-path-for-ramblock-id" only with new qemus which have the stable version (this is what we would usually do)

2b) we also add support for "x-use-canonical-path-for-ramblock-id" but detection will be limited to existing releases Supporting "x-use-canonical-path-for-ramblock-id" for any future release of qemu without a clear declaration that it's considered stable in qemu is not acceptable for libvirt.