Kevin Wolf <kw...@redhat.com> writes: > Am 28.09.2020 um 09:47 hat Markus Armbruster geschrieben: >> 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? > > Interleaving, or rather executing another command in the middle of its > implementation is the very purpose of human-monitor-command (which is > what I was talking about, so "the in-band non-coroutine QMP command" is > a very specific one).
Got it now, thanks. > It's the only command I can think of that is exceptional in this way > and would lead to three mappings. > > Kevin
