Re: [Qemu-devel] [PATCH v2 2/3] Add 'debug-threads' suboption to --name

[Laszlo Ersek]

On 02/10/14 11:16, Dr. David Alan Gilbert wrote:
> * Laszlo Ersek (address@hidden) wrote:
>> a few irrelevant comments below:
>>
>> On 01/30/14 11:20, Dr. David Alan Gilbert (git) wrote:
>>> From: "Dr. David Alan Gilbert" <address@hidden>
>>>
>>> Add flag storage to qemu-thread-* to store the namethreads flag
>>>
>>> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
>>> ---
>>>  include/qemu/thread.h    | 1 +
>>>  qemu-options.hx          | 7 +++++--
>>>  util/qemu-thread-posix.c | 7 +++++++
>>>  util/qemu-thread-win32.c | 8 ++++++++
>>>  vl.c                     | 9 +++++++++
>>>  5 files changed, 30 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/qemu/thread.h b/include/qemu/thread.h
>>> index 3e32c65..bf1e110 100644
>>> --- a/include/qemu/thread.h
>>> +++ b/include/qemu/thread.h
>>> @@ -59,5 +59,6 @@ void *qemu_thread_join(QemuThread *thread);
>>>  void qemu_thread_get_self(QemuThread *thread);
>>>  bool qemu_thread_is_self(QemuThread *thread);
>>>  void qemu_thread_exit(void *retval);
>>> +void qemu_thread_naming(bool enable);
>>>  
>>>  #endif
>>> diff --git a/qemu-options.hx b/qemu-options.hx
>>> index 56e5fdf..068da2d 100644
>>> --- a/qemu-options.hx
>>> +++ b/qemu-options.hx
>>> @@ -328,9 +328,11 @@ possible drivers and properties, use @code{-device 
>>> help} and
>>>  ETEXI
>>>  
>>>  DEF("name", HAS_ARG, QEMU_OPTION_name,
>>> -    "-name string1[,process=string2]\n"
>>> +    "-name string1[,process=string2][,debug-threads=on|off]\n"
>>>      "                set the name of the guest\n"
>>> -    "                string1 sets the window title and string2 the process 
>>> name (on Linux)\n",
>>> +    "                string1 sets the window title and string2 the process 
>>> name (on Linux)\n"
>>> +    "                When debug-threads is enabled, individual threads are 
>>> given a separate name (on Linux)\n"
>>> +    "                NOTE: The thread names are for debugging and not a 
>>> stable API.\n",
>>>      QEMU_ARCH_ALL)
>>>  STEXI
>>>  @item -name @var{name}
>>> @@ -339,6 +341,7 @@ Sets the @var{name} of the guest.
>>>  This name will be displayed in the SDL window caption.
>>>  The @var{name} will also be used for the VNC server.
>>>  Also optionally set the top visible process name in Linux.
>>> +Naming of individual threads can also be enabled on Linux to aid debugging.
>>>  ETEXI
>>>  
>>>  DEF("uuid", HAS_ARG, QEMU_OPTION_uuid,
>>> diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
>>> index 37dd298..0fa6c81 100644
>>> --- a/util/qemu-thread-posix.c
>>> +++ b/util/qemu-thread-posix.c
>>> @@ -27,6 +27,13 @@
>>>  #include "qemu/thread.h"
>>>  #include "qemu/atomic.h"
>>>  
>>> +static bool name_threads;
>>> +
>>> +void qemu_thread_naming(bool enable)
>>> +{
>>> +    name_threads = enable;
>>> +}
>>> +
>>>  static void error_exit(int err, const char *msg)
>>>  {
>>>      fprintf(stderr, "qemu: %s: %s\n", msg, strerror(err));
>>> diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
>>> index 27a5217..e42cb77 100644
>>> --- a/util/qemu-thread-win32.c
>>> +++ b/util/qemu-thread-win32.c
>>> @@ -16,6 +16,14 @@
>>>  #include <assert.h>
>>>  #include <limits.h>
>>>  
>>> +static bool name_threads;
>>> +
>>> +void qemu_thread_naming(bool enable)
>>> +{
>>> +    /* But note we don't actually name them on Windows yet */
>>> +    name_threads = enable;
>>> +}
>>> +
>>>  static void error_exit(int err, const char *msg)
>>>  {
>>>      char *pstr;
>>> diff --git a/vl.c b/vl.c
>>> index 5f993e4..77d6d9e 100644
>>> --- a/vl.c
>>> +++ b/vl.c
>>> @@ -547,6 +547,12 @@ static QemuOptsList qemu_name_opts = {
>>>              .name = "process",
>>>              .type = QEMU_OPT_STRING,
>>>              .help = "Sets the name of the QEMU process, as shown in top 
>>> etc",
>>> +        }, {
>>> +            .name = "debug-threads",
>>> +            .type = QEMU_OPT_BOOL,
>>> +            .help = "When enabled, name the individual threads; defaults 
>>> off.\n"
>>
>> (1) same question about newlines applies
> 
> I'd assumed this landed in -help output and that looked OK.
> 
>> (2) the default setting is usually advertised in qemu-options.hx, not here
> 
> OK
> 
>> (3) the meaning of "default" is relative to the case when the option is
>> specified and the option argument is not, *not* relative to when the
>> option is missing. Cf.
>>
>> (a)  -name debug-threads
>> (b)  -name debug-threads=on
>> (c)  [nothing]
>>
>> The default as explained by the help text (in qemu-options.hx),
>> independently of option argument type, is usually the difference between
>> (a) and (b), not (a) and (c), nor between (b) and (c).
>>
>> Here, due to the way boolean options are parsed in parse_option_bool(),
>> (a) is identical to (b), so the default is "on". (See -msg timestamp in
>> qemu-options.hx, it's similar.)
>>
>> I *think*. But I could never really form a decisive understanding of the
>> tradition here, so feel free to ignore it.
> 
> If 'default' is (a) then what is the word for (c) ? What I was really
> trying to express was that if you don't pass the option at all it's
> not going to name the threads.

I see. I couldn't name an example where (c) is explicitly referred to.

Thanks
Laszlo