Hi On Fri, Apr 16, 2021 at 6:59 PM Marc-André Lureau < marcandre.lureau@gmail.com> wrote: > Hi > > On Fri, Apr 16, 2021 at 6:51 PM Markus Armbruster > wrote: > >> Marc-André, I'd like your opinion for this one, in particular the use of >> g_source_remove(). >> > > My opinion isn't really worth much, my review would have a bit more value. > > GSource has indeed some peculiar lifetime management, that I got wrong in > the past. So I would be extra careful. > > But before spending time on review, I would also clarify the motivation > and ask for testing. > > Markus, hot-adding/removing monitors isn't supported? > > I realize you answered my question below. That's surprising me. Wouldn't it make more sense to support it rather than having a pre-opened null-based monitor that can have its chardev swapped? > >> Li Zhang writes: >> >> > For some scenarios, it needs to hot-add a monitor device. >> > But QEMU doesn't support hotplug yet. It also works by adding >> > a monitor with null backend by default and then change its >> > backend to socket by QMP command "chardev-change". >> > >> > So this patch is to support monitor chardev hotswap with QMP. >> > >> > Signed-off-by: Li Zhang >> > Reviewed-by: Pankaj Gupta >> >> Your commit message starts with a brief description of the problem. >> Appreciated! But I think it could be a bit clearer. What about this: >> >> qmp: Support chardev-change >> >> For some scenarios, we'd like to hot-add a monitor device. But QEMU >> doesn't support that, yet. It does support hot-swapping character >> backends with QMP command chardev-change. This lets us pre-add a >> monitor with a null character backend, then chardev-change to a >> socket backend. Except the chardev-change fails with "Chardev user >> does not support chardev hotswap" because monitors don't provide the >> required callback. Implement it for QMP monitors. >> >> > --- >> > v1 -> v2: >> > - Change mutex lock mon_lock section >> > - Fix indentation problems >> > >> > monitor/monitor-internal.h | 3 +++ >> > monitor/monitor.c | 2 +- >> > monitor/qmp.c | 43 +++++++++++++++++++++++++++++++++++--- >> > 3 files changed, 44 insertions(+), 4 deletions(-) >> > >> > diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h >> > index 9c3a09cb01..1b80c74883 100644 >> > --- a/monitor/monitor-internal.h >> > +++ b/monitor/monitor-internal.h >> > @@ -183,4 +183,7 @@ void help_cmd(Monitor *mon, const char *name); >> > void handle_hmp_command(MonitorHMP *mon, const char *cmdline); >> > int hmp_compare_cmd(const char *name, const char *list); >> > >> > +gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond, >> > + void *opaque); >> > + >> > #endif >> > diff --git a/monitor/monitor.c b/monitor/monitor.c >> > index 636bcc81c5..16a3620d02 100644 >> > --- a/monitor/monitor.c >> > +++ b/monitor/monitor.c >> > @@ -157,7 +157,7 @@ static inline bool >> monitor_is_hmp_non_interactive(const Monitor *mon) >> > >> > static void monitor_flush_locked(Monitor *mon); >> > >> > -static gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond, >> > +gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond, >> > void *opaque) >> > { >> > Monitor *mon = opaque; >> > diff --git a/monitor/qmp.c b/monitor/qmp.c >> > index 2b0308f933..5fa65401ae 100644 >> > --- a/monitor/qmp.c >> > +++ b/monitor/qmp.c >> > @@ -44,6 +44,7 @@ struct QMPRequest { >> > Error *err; >> > }; >> > typedef struct QMPRequest QMPRequest; >> > +static void monitor_qmp_set_handlers_bh(void *opaque); >> > >> > QmpCommandList qmp_commands, qmp_cap_negotiation_commands; >> > >> > @@ -477,7 +478,36 @@ void monitor_data_destroy_qmp(MonitorQMP *mon) >> > g_queue_free(mon->qmp_requests); >> > } >> > >> > -static void monitor_qmp_setup_handlers_bh(void *opaque) >> > +static int monitor_qmp_change (void *opaque) >> > +{ >> > + MonitorQMP *mon = opaque; >> > + >> > + mon->common.use_io_thread = >> qemu_chr_has_feature(mon->common.chr.chr, >> > + QEMU_CHAR_FEATURE_GCONTEXT); >> > + >> > + if (mon->common.use_io_thread) { >> > + aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread), >> > + monitor_qmp_set_handlers_bh, mon); >> > + } else { >> > + qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read, >> > + monitor_qmp_read, monitor_qmp_event, >> > + monitor_qmp_change, &mon->common, >> NULL, true); >> > + } >> > + >> > + qemu_mutex_lock(&mon->common.mon_lock); >> > + if (mon->common.out_watch) { >> > + g_source_remove(mon->common.out_watch); >> > + mon->common.out_watch = qemu_chr_fe_add_watch(&mon->common.chr, >> > + G_IO_OUT | G_IO_HUP, >> > + monitor_unblocked, >> > + &mon->common); >> >> Visually align the arguments: >> >> mon->common.out_watch = qemu_chr_fe_add_watch(&mon->common.chr, >> G_IO_OUT | G_IO_HUP, >> monitor_unblocked, >> &mon->common); >> >> You may reduce argument indentation some to gain extra space, but keep >> the arguments more indented than the function: >> >> mon->common.out_watch = qemu_chr_fe_add_watch(&mon->common.chr, >> G_IO_OUT | G_IO_HUP, >> monitor_unblocked, &mon->common); >> >> Do this only when you actually use the extra space for readability. >> >> > + } >> > + qemu_mutex_unlock(&mon->common.mon_lock); >> > + >> > + return 0; >> > +} >> >> As I wrote in my review of v1, this function copies from >> monitor_data_init(), monitor_init_qmp(), and monitor_flush_locked(). >> Feels like a refactoring would be in order. Doing it on top might be >> easier. >> >> > + >> > +static void monitor_qmp_set_handlers_bh(void *opaque) >> > { >> > MonitorQMP *mon = opaque; >> > GMainContext *context; >> > @@ -487,7 +517,14 @@ static void monitor_qmp_setup_handlers_bh(void >> *opaque) >> > assert(context); >> > qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read, >> > monitor_qmp_read, monitor_qmp_event, >> > - NULL, &mon->common, context, true); >> > + monitor_qmp_change, &mon->common, >> context, true); >> > + >> > +} >> > + >> > +static void monitor_qmp_setup_handlers_bh(void *opaque) >> > +{ >> > + MonitorQMP *mon = opaque; >> > + monitor_qmp_set_handlers_bh(mon); >> > monitor_list_append(&mon->common); >> > } >> > >> > @@ -528,7 +565,7 @@ void monitor_init_qmp(Chardev *chr, bool pretty, >> Error **errp) >> > } else { >> > qemu_chr_fe_set_handlers(&mon->common.chr, monitor_can_read, >> > monitor_qmp_read, monitor_qmp_event, >> > - NULL, &mon->common, NULL, true); >> > + monitor_qmp_change, &mon->common, >> NULL, true); >> > monitor_list_append(&mon->common); >> > } >> > } >> >> >> > > -- > Marc-André Lureau > -- Marc-André Lureau