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?
Li Zhang <zhlcindy@gmail.com> 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 <li.zhang@cloud.ionos.com>
> Reviewed-by: Pankaj Gupta <pankaj.gupta@ionos.com>
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);
> }
> }