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

[Steven Sistare]

On 9/11/2020 1:59 PM, Dr. David Alan Gilbert wrote:
> * Steven Sistare (steven.sistare@oracle.com) wrote:
>> 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.
> 
> You might try the '--preconfig' option - that's pretty early on.
> The other one is adding a chardev and telling it to wait for a server;
> that'll wait until you telnet to the port.
> 
> (Either way, this patch shouldn't really be part of this series, it's a
> separate discussion)

Sure, I will pull it from the series.

- Steve

>> - 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;
>>>
>>>
>>