Preserve current monitor CPU when issuing HMP passthrough commands

From: "Daniel P. Berrange"<[email protected]>

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<[email protected]>

---
  monitor.c |    3 +++
  1 files changed, 3 insertions(+), 0 deletions(-)

monitor.c +3 -0

index 421a65c..f99659d 100644
@@ -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));