Eric Blake <ebl...@redhat.com> writes: > On 11/27/19 9:49 AM, Eric Blake wrote: >> On 11/27/19 7:30 AM, Markus Armbruster wrote: >> >>> "Good enough" was true back then. It wasn't true when we reused it for >>> netdev_add: hostfwd and guestfwd are list-valued. >>> >>> We did define a QAPI schema a few months later (14aa0c2de0 "qapi schema: >>> add Netdev types"). net_client_init() uses it to convert from QemuOpts >>> to QAPI type Netdev. This took us to the crazy pipeline we still use >>> today: >>> >>> CLI, HMP >>> (key=value,...) >>> | >>> v >>> QMP (JSON) -> QDict -> QemuOpts -> Netdev >>> >>> We should instead use: >>> >>> CLI, HMP >>> (key=value,...) >>> | >>> v >>> QemuOpts >>> | >>> v >>> QMP (JSON) -> QDict -> Netdev >>> >>> Back in 2016, Eric (cc'ed) posted patches to get us to this pipeline. >>> They got stuck on backward compatibility worries: the old code accepts >>> all parameters as JSON strings in addition to their proper type, the new >>> code doesn't. Undocumented misfeature, but we chickened out anyway. >> >> That was before we had a deprecation process. Now we do. If we are >> still worried about it, then we should start the deprecation clock >> (squeezing it into 4.2-rc3 is risky, more likely is starting it in >> 5.0, so that we get rid of string support in 5.2). If we are not >> worried about it, then we can just kill the misfeature in 5.0. > > I'm leaning towards just killing the misfeature (it's a lot of glue > code to add to support the misfeature for 5.0 and 5.1, if we're just > going to rip it back out for 5.2), especially since introspection is > enough for any affected clients to learn about the stricter behavior.
Here's my practical argument for simply killing it without further delay. We have a bug we know to affect users: the one reported by Alex. We have a misfeature users may or may not rely on: the one that made us chicken out. To fix the bug, we have to kill the misfeature. Fixing it without killing the misfeature feels impractical. For 5.0, it's flat-out impossible. Deprecating the misfeature for a grace period before we kill it means letting the bug continue to bite users for the whole grace period. Since we lack the means to communicate "you're using a deprecate misfeature, stop it!" to QMP clients, the deprecation grace period is unlikely to help much. >>> Let's reconsider. Eric's patches break interface misuse that may or may >>> not exist in the field. They fix a correct use of interface people want >>> to use (or Alex wouldn't have reported this bug), and they make QMP >>> introspection work for netdev_add. >>> >>> Eric, what do you think? >> >> Yes, it's time to revive that work (I have no idea if my patches >> from back then will still rebase nicely, though). > > Now posted: > https://lists.gnu.org/archive/html/qemu-devel/2020-03/msg03842.html Thanks, I'll review.
