Kevin Wolf <kw...@redhat.com> writes: > Am 14.09.2020 um 17:11 hat Markus Armbruster geschrieben: >> Kevin Wolf <kw...@redhat.com> writes: >> >> > This way, a monitor command handler will still be able to access the >> > current monitor, but when it yields, all other code code will correctly >> > get NULL from monitor_cur(). >> > >> > This uses a hash table to map the coroutine pointer to the current >> > monitor of that coroutine. Outside of coroutine context, we associate >> > the current monitor with the leader coroutine of the current thread. >> >> In qemu-system-FOO, the hash table can have only these entries: >> >> * (OOB) One mapping @mon_iothread's thread leader to a QMP monitor, while >> executing a QMP command out-of-band. >> >> * (QMP-CO) One mapping @qmp_dispatcher_co (a coroutine in the main >> thread) to a QMP monitor, while executing a QMP command in-band and in >> coroutine context. >> >> * (QMP) One mapping the main thread's leader to a QMP monitor, while >> executing a QMP command in-band and out of coroutine context, in a >> bottom half. >> >> * (HMP) One mapping the main thread's leader to an HMP monitor, while >> executing an HMP command out of coroutine context. >> >> * (HMP-CO) One mapping a transient coroutine in the main thread to an >> HMP monitor, while executing an HMP command in coroutine context. >> >> In-band execution is one command after the other. >> >> Therefore, at most one monitor command can be executing in-band at any >> time. >> >> Therefore, the hash table has at most *two* entries: one (OOB), and one >> of the other four. >> >> Can you shoot any holes into my argument? > > I think with human-monitor-command, you can have three mappings: > > 1. The main thread's leader (it is a non-coroutine QMP command) to the > QMP monitor
This is (QMP). > 2. With a coroutine HMP command, one mapping from the transient HMP > coroutine to the transient HMP monitor (with a non-coroutine HMP > command, we'd instead temporarily change the mapping from 1.) This is (HMP-CO). > 3. The OOB entry This is (OOB). To get 1. (QMP) and 2, (HMP-CO) at the same time, the in-band, non-coroutine QMP command needs to execute interleaved with the in-band, coroutine HMP command. Such an interleaving contradicts "In-band execution is one command after the other", which is a fundamental assumption in-band commands may make. If the assumption is invalid, we got a problem. Is it? >> I suspect there's a simpler solution struggling to get out. But this >> solution works, so in it goes. Should the simpler one succeed at >> getting out, it can go in on top. If not, I'll probably add even more >> comments to remind myself of these facts. > > I think the simple approach you had posted could work if you can fill in > the HMP part, but I think it wasn't completely trivial and you told me > not to bother for now, Correct. I decided to go with the code you already tested. > so I didn't. It may still be a viable path > forward if you like it better.
