[Qemu-devel] [PATCH] Preserve current monitor CPU when issuing HMP passthrough commands

["Daniel P. Berrange" <berrange@redhat.com>]

From: "Daniel P. Berrange" <berrange@redhat.com>

Several info commands rely on the 'mon_cpu' field in the Monitor
struct. This field can be updated using the 'cpu NN' command.

The processing for HMP passthrough commands, however, does not
use the global 'Monitor *' instance, instead creating a brand
new instance on the stack for HMP command executed. This breaks
anything setting/getting the current monitor CPU

 $ ./x86_64-softmmu/qemu-system-x86_64 -cdrom ~/boot.iso -qmp stdio -smp 4
 {"QMP": {"version": {"qemu": {"micro": 50, "minor": 15, "major": 0}, "package": ""}, "capabilities": []}}
 {"execute":"qmp_capabilities"}
 {"return": {}}
 {"execute":"human-monitor-command","arguments":{"command-line":"info cpus"}}
 {"return": "* CPU #0: pc=0x000000000010017c (halted) thread_id=2570 \r\n  CPU #1: pc=0x00000000000ff0a2 (halted) thread_id=2570 \r\n  CPU #2: pc=0x00000000000ff0a2 (halted) thread_id=2570 \r\n  CPU #3: pc=0x00000000000ff0a2 (halted) thread_id=2570 \r\n"}
 {"execute":"human-monitor-command","arguments":{"command-line":"cpu 2"}}
 {"return": {}}
 {"execute":"human-monitor-command","arguments":{"command-line":"info cpus"}}
 {"return": "* CPU #0: pc=0x000000000010017c (halted) thread_id=2570 \r\n  CPU #1: pc=0x00000000000ff0a2 (halted) thread_id=2570 \r\n  CPU #2: pc=0x00000000000ff0a2 (halted) thread_id=2570 \r\n  CPU #3: pc=0x00000000000ff0a2 (halted) thread_id=2570 \r\n"}

In that example, the '*' should have moved from CPU #0, to CPU #2
but it did not.

The simple fix is to just copy the existing 'mon_cpu' field into
the new temporary Monitor instance, before the HMP command is
run, and copy the updated value back to the global instance
afterwards.

* monitor.c: Track 'mon_cpu' when doing HMP passthrough

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 monitor.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/monitor.c b/monitor.c
index 421a65c..f99659d 100644
--- a/monitor.c
+++ b/monitor.c
@@ -513,6 +513,7 @@ static int do_hmp_passthrough(Monitor *mon, const QDict *params,
     memset(&hmp, 0, sizeof(hmp));
     qemu_chr_init_mem(&mchar);
     hmp.chr = &mchar;
+    hmp.mon_cpu = cur_mon->mon_cpu;
 
     old_mon = cur_mon;
     cur_mon = &hmp;
@@ -521,6 +522,7 @@ static int do_hmp_passthrough(Monitor *mon, const QDict *params,
         ret = mon_set_cpu(qdict_get_int(params, "cpu-index"));
         if (ret < 0) {
             cur_mon = old_mon;
+            cur_mon->mon_cpu = hmp.mon_cpu;
             qerror_report(QERR_INVALID_PARAMETER_VALUE, "cpu-index", "a CPU number");
             goto out;
         }
@@ -528,6 +530,7 @@ static int do_hmp_passthrough(Monitor *mon, const QDict *params,
 
     handle_user_command(&hmp, qdict_get_str(params, "command-line"));
     cur_mon = old_mon;
+    cur_mon->mon_cpu = hmp.mon_cpu;
 
     if (qemu_chr_mem_osize(hmp.chr) > 0) {
         *ret_data = QOBJECT(qemu_chr_mem_to_qs(hmp.chr));
-- 
1.7.6