Re: [PATCH V1 12/32] vl: pause option

[Steven Sistare <steven.sistare@oracle.com>]

On 7/30/2020 1:03 PM, Alex Bennée wrote:
> 
> Steve Sistare <steven.sistare@oracle.com> writes:
> 
>> Provide the -pause command-line parameter and the QEMU_PAUSE environment
>> variable to briefly pause QEMU in main and allow a developer to attach gdb.
>> Useful when the developer does not invoke QEMU directly, such as when using
>> libvirt.
> 
> How does this differ from -S?

The -S flag runs qemu to the main loop but does not start the guest.  Lots of code
that you may need to debug runs before you get there.

- Steve
>> Usage:
>>   qemu -pause <seconds>
>>   or
>>   export QEMU_PAUSE=<seconds>
>>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>  qemu-options.hx |  9 +++++++++
>>  softmmu/vl.c    | 15 ++++++++++++++-
>>  2 files changed, 23 insertions(+), 1 deletion(-)
>>
>> diff --git a/qemu-options.hx b/qemu-options.hx
>> index 708583b..8505cf2 100644
>> --- a/qemu-options.hx
>> +++ b/qemu-options.hx
>> @@ -3668,6 +3668,15 @@ SRST
>>      option is experimental.
>>  ERST
>>  
>> +DEF("pause", HAS_ARG, QEMU_OPTION_pause, \
>> +    "-pause secs    Pause for secs seconds on entry to main.\n", QEMU_ARCH_ALL)
>> +
>> +SRST
>> +``--pause secs``
>> +    Pause for a number of seconds on entry to main.  Useful for attaching
>> +    a debugger after QEMU has been launched by some other entity.
>> +ERST
>> +
> 
> It seems like having an option to race with the debugger is just asking
> for trouble.
> 
>>  DEF("S", 0, QEMU_OPTION_S, \
>>      "-S              freeze CPU at startup (use 'c' to start execution)\n",
>>      QEMU_ARCH_ALL)
>> diff --git a/softmmu/vl.c b/softmmu/vl.c
>> index 8478778..951994f 100644
>> --- a/softmmu/vl.c
>> +++ b/softmmu/vl.c
>> @@ -2844,7 +2844,7 @@ static void create_default_memdev(MachineState *ms, const char *path)
>>  
>>  void qemu_init(int argc, char **argv, char **envp)
>>  {
>> -    int i;
>> +    int i, seconds;
>>      int snapshot, linux_boot;
>>      const char *initrd_filename;
>>      const char *kernel_filename, *kernel_cmdline;
>> @@ -2882,6 +2882,13 @@ void qemu_init(int argc, char **argv, char **envp)
>>      QemuPluginList plugin_list = QTAILQ_HEAD_INITIALIZER(plugin_list);
>>      int mem_prealloc = 0; /* force preallocation of physical target memory */
>>  
>> +    if (getenv("QEMU_PAUSE")) {
>> +        seconds = atoi(getenv("QEMU_PAUSE"));
>> +        printf("Pausing %d seconds for debugger. QEMU PID is %d\n",
>> +               seconds, getpid());
>> +        sleep(seconds);
>> +    }
>> +
>>      os_set_line_buffering();
>>  
>>      error_init(argv[0]);
>> @@ -3204,6 +3211,12 @@ void qemu_init(int argc, char **argv, char **envp)
>>              case QEMU_OPTION_gdb:
>>                  add_device_config(DEV_GDB, optarg);
>>                  break;
>> +            case QEMU_OPTION_pause:
>> +                seconds = atoi(optarg);
>> +                printf("Pausing %d seconds for debugger. QEMU PID is %d\n",
>> +                            seconds, getpid());
>> +                sleep(seconds);
>> +                break;
>>              case QEMU_OPTION_L:
>>                  if (is_help_option(optarg)) {
>>                      list_data_dirs = true;
> 
>