Message ID | 20201026101005.2940615-1-armbru@redhat.com (mailing list archive) |
---|---|
Headers | show |
Series | qemu-storage-daemon: QAPIfy --chardev the stupid way | expand |
On 26/10/20 11:10, Markus Armbruster wrote: > Kevin's "[PATCH v2 0/6] qemu-storage-daemon: QAPIfy --chardev" > involves surgery to the QAPI generator. Some (most?) of it should go > away if we deprecate the "data" wrappers due to simple unions in QMP. > > Do we really need to mess with the code generator to solve the problem > at hand? > > > Let's recapitulate the problem: > > * We want to QAPIfy --chardev, i.e. define its argument as a QAPI > type. Considering that this is not 5.2 stuff at this point, I would like to suggest again moving chardevs to -object, and ask you to evaluate that option with the agreement that I do the work instead of you. :) Paolo
Paolo Bonzini <pbonzini@redhat.com> writes: > On 26/10/20 11:10, Markus Armbruster wrote: >> Kevin's "[PATCH v2 0/6] qemu-storage-daemon: QAPIfy --chardev" >> involves surgery to the QAPI generator. Some (most?) of it should go >> away if we deprecate the "data" wrappers due to simple unions in QMP. >> >> Do we really need to mess with the code generator to solve the problem >> at hand? >> >> >> Let's recapitulate the problem: >> >> * We want to QAPIfy --chardev, i.e. define its argument as a QAPI >> type. > > Considering that this is not 5.2 stuff at this point, I would like to > suggest again moving chardevs to -object, and ask you to evaluate that > option with the agreement that I do the work instead of you. :) Replacing -chardev with -object without regressing features would be lovely. One feature in particular: introspection. If we manage to fully QAPIfy -object, we should be good. I understand Eduardo is cutting a path through the jungle. I can offer assistance with bridging QAPI schema to QOM.
Am 28.10.2020 um 08:01 hat Markus Armbruster geschrieben: > Paolo Bonzini <pbonzini@redhat.com> writes: > > > On 26/10/20 11:10, Markus Armbruster wrote: > >> Kevin's "[PATCH v2 0/6] qemu-storage-daemon: QAPIfy --chardev" > >> involves surgery to the QAPI generator. Some (most?) of it should go > >> away if we deprecate the "data" wrappers due to simple unions in QMP. > >> > >> Do we really need to mess with the code generator to solve the problem > >> at hand? > >> > >> > >> Let's recapitulate the problem: > >> > >> * We want to QAPIfy --chardev, i.e. define its argument as a QAPI > >> type. > > > > Considering that this is not 5.2 stuff at this point, I would like to > > suggest again moving chardevs to -object, and ask you to evaluate that > > option with the agreement that I do the work instead of you. :) I don't think this is the right thing to do at this point. Making more use of QOM is an orthogonal problem and would only make solving this one harder. The problem we have and we're trying to solve is that we have chardev-add (which has a QAPI schema) and -chardev (which doesn't). We want to get an option that is described by the schema, doesn't duplicate things and is still convenient to use. Whether this option starts with -chardev or with -object doesn't really make much of a difference. The QAPI schema you need behind it will be almost or even exactly the same. > Replacing -chardev with -object without regressing features would be > lovely. One feature in particular: introspection. > > If we manage to fully QAPIfy -object, we should be good. I understand > Eduardo is cutting a path through the jungle. I don't expect many difficulties with the existing -object (famous last words). But if you make chardevs user creatable objects first, it becomes much harder because you just combined two problems (one of which is already known to be hard) into one large problem. > I can offer assistance with bridging QAPI schema to QOM. So, the steps that I would suggest are: 1a. Finish the QAPI schema for object-add 1b. Find some way to unify chardev-add's ChardevBackend and a CLI-friendly version of it in the schema 2. Generate QOM boilerplate code from ObjectOptions instead of duplicating it in the implementation 3. Convert chardevs to using QOM properites only now If we do 3. earlier, we'll write code that we want to replace later anyway. If we even do it in parallel with 1b. we'll additionally get merge conflicts. And if we do it before 1b. we'll do it without considering QAPI in detail and will lose any flexibility to change things in the new interface, which will make 1b. much harder. Kevin
On 28/10/20 12:46, Kevin Wolf wrote: > I don't think this is the right thing to do at this point. Making more > use of QOM is an orthogonal problem and would only make solving this one > harder. Making more use of QOM will make this a non-problem. You'll just use object-add and -object and, when you figure out the QOM schema, it will just work. Paolo > The problem we have and we're trying to solve is that we have > chardev-add (which has a QAPI schema) and -chardev (which doesn't). We > want to get an option that is described by the schema, doesn't duplicate > things and is still convenient to use. > > Whether this option starts with -chardev or with -object doesn't really > make much of a difference. The QAPI schema you need behind it will be > almost or even exactly the same.
Am 28.10.2020 um 15:39 hat Paolo Bonzini geschrieben: > On 28/10/20 12:46, Kevin Wolf wrote: > > I don't think this is the right thing to do at this point. Making more > > use of QOM is an orthogonal problem and would only make solving this one > > harder. > > Making more use of QOM will make this a non-problem. You'll just use > object-add and -object and, when you figure out the QOM schema, it will > just work. Yes, but figuring out the QOM schema (or rather, what the interface represented by the schema should look like) is the hard part. It is exactly the same hard part that we're currently trying to figure out without also worrying about QOM at the same time. -object and object-add instead of -chardev and chardev-add change the spelling, but solve none of these problems. Kevin
On 28/10/20 15:59, Kevin Wolf wrote: >> Making more use of QOM will make this a non-problem. You'll just use >> object-add and -object and, when you figure out the QOM schema, it will >> just work. > > Yes, but figuring out the QOM schema (or rather, what the interface > represented by the schema should look like) is the hard part. I don't disagree with that, but it's a problem you have to solve anyway, isn't it? Once you figure out how to introspect QOM classes, that would apply just as well to character devices. On the other hand, creating character devices with -object does solve another problem, namely the distinction between "early" and "late" objects in vl.c, in a way that QAPIfied -chardev doesn't solve. Paolo
Am 28.10.2020 um 16:09 hat Paolo Bonzini geschrieben: > On 28/10/20 15:59, Kevin Wolf wrote: > >> Making more use of QOM will make this a non-problem. You'll just use > >> object-add and -object and, when you figure out the QOM schema, it will > >> just work. > > > > Yes, but figuring out the QOM schema (or rather, what the interface > > represented by the schema should look like) is the hard part. > > I don't disagree with that, but it's a problem you have to solve anyway, > isn't it? Once you figure out how to introspect QOM classes, that would > apply just as well to character devices. Yes, it's the problem I tried to address with my series, and Markus with this alternative series. We need to do this either way. > On the other hand, creating character devices with -object does solve > another problem, namely the distinction between "early" and "late" > objects in vl.c, in a way that QAPIfied -chardev doesn't solve. Right. Both are solving different problems, and solving one won't automatically make the other a non-problem as you suggested above. I just suggested leaving QOM for later because two people making big changes on the same subsystem is going to be painful for at least one of them, and because for adding QOM properties, you need to know what these properties should look like (unless you want to change them again later). If you don't wait for the QAPI work, you'll have solved the problem of having two separate ways to describe chardev options by making it three separate ways. Technically this might fulfill the condition of not having two separate ways, but it's not really what we had in mind. :-) Kevin
On 28/10/20 16:39, Kevin Wolf wrote: >> I don't disagree with that, but it's a problem you have to solve anyway, >> isn't it? Once you figure out how to introspect QOM classes, that would >> apply just as well to character devices. > Yes, it's the problem I tried to address with my series, and Markus with > this alternative series. We need to do this either way. Right, I appreciate that QOMifying chardev would only be a solution if QOM introspection gets into 6.0. This is why I only brought it up because neither of these series will be ready in time for 5.2. So maybe QOMifying chardev wouldn't make it a non-problem; it would make it someone else's (Eduardo's) problem. > you need to know what these properties should look like True that. But I think the existing QAPI structures do help for that. > If you don't wait for the QAPI work, you'll have solved the problem of > having two separate ways to describe chardev options by making it three > separate ways. Technically this might fulfill the condition of not > having two separate ways, but it's not really what we had in mind. :-) Actually four ways (-chardev, chardev-add, -object, object-add) but two of them would be implemented by the same code and qsd would be able to standardize on them. Paolo