Re: [Qemu-devel] [PATCH v2 1/3] qemu-io: Add sigraise command

[Markus Armbruster]

Max Reitz <address@hidden> writes:

> On 2014-12-05 at 10:52, Markus Armbruster wrote:
>> Max Reitz <address@hidden> writes:
>>
>>> abort() has the sometimes undesirable side-effect of generating a core
>>> dump. If that is not needed, SIGKILL has the same effect of abruptly
>>> crash qemu; without a core dump.
>>>
>>> Thus, -c abort is not always useful to simulate a qemu-io crash;
>>> therefore, this patch adds a new sigraise command which allows to raise
>>> any Unix signal.
>> Nitpick: signals are ISO C, not just UNIX.
>
> Yes, but "Unix signal" is what the Wikipedia article is named, so... ;-)

If it's in Wikipedia, it must be right!  Quick, file a bug against the C
standard!

>>> Signed-off-by: Max Reitz <address@hidden>
>>> ---
>>>   qemu-io-cmds.c | 46 ++++++++++++++++++++++++++++++++++++++++++++++
>>>   1 file changed, 46 insertions(+)
>>>
>>> diff --git a/qemu-io-cmds.c b/qemu-io-cmds.c
>>> index d94fb1e..942b694 100644
>>> --- a/qemu-io-cmds.c
>>> +++ b/qemu-io-cmds.c
>>> @@ -2048,6 +2048,51 @@ static const cmdinfo_t abort_cmd = {
>>>          .oneline        = "simulate a program crash using abort(3)",
>>>   };
>>>   +static void sigraise_help(void)
>>> +{
>>> +    printf(
>>> +"\n"
>>> +" raises the given Unix signal\n"
>>> +"\n"
>>> +" Example:\n"
>>> +" 'sigraise 9' - raises SIGKILL\n"
>> Assumes SIGKILL is encoded as 9, which is traditionally the case, but
>> not actually mandated by POSIX.
>
> Yes, I know. The best would be to parse the signal like kill(1) does,
> but that would have been extra difficult and probably not worth the
> effort.

Agree.

> Furthermore, I know there is a song called "kill dash nine", so I
> guessed it would be enough (at least it'll have to be enough for test
> 039, thanks to "_supported_os Linux").

Bash can map signal names to numbers and back:

    $ kill -l 9
    KILL
    $ kill -l KILL
    9

Perhaps you can use that to avoid hardcoding.

>> You could avoid hardcoding 9 with
>>
>>      " 'sigraise %d' - raises SIGKILL\n"
>>
>> with a SIGKILL as argument for %d.
>
> Clever. Will do.
>
>> But then you'd have to face the fact that SIGKILL is POSIX, not ISO C.
>> The ISO C signals are SIGABRT, SIGFPE, SIGILL, SIGINT, SIGSEGV, SIGTERM.
>> Of these, SIGINT and SIGTERM don't dump core, in case you care.
>
> Good to know. I guess I'll just go with SIGKILL anyway, it's
> ubiquitous enough.

Might break the Windows compile.

>>> +"\n"
>>> +" Invokes raise(signal), where \"signal\" is the mandatory integer 
>>> argument\n"
>>> +" given to sigraise.\n"
>>> +"\n");
>>> +}
>>> +
>>> +static int sigraise_f(BlockDriverState *bs, int argc, char **argv);
>>> +
>>> +static const cmdinfo_t sigraise_cmd = {
>>> +    .name       = "sigraise",
>>> +    .cfunc      = sigraise_f,
>>> +    .argmin     = 1,
>>> +    .argmax     = 1,
>>> +    .flags      = CMD_NOFILE_OK,
>>> +    .args       = "signal",
>>> +    .oneline    = "raises a Unix signal",
>>> +    .help       = sigraise_help,
>>> +};
>>> +
>>> +static int sigraise_f(BlockDriverState *bs, int argc, char **argv)
>>> +{
>>> +    int sig = cvtnum(argv[1]);
>>> +    if (sig < 0) {
>>> +        printf("non-numeric signal number argument -- %s\n", argv[1]);
>>> +        return 0;
>>> +    }
>>> +
>>> +    /* Using raise() to kill this process does not necessarily flush all 
>>> open
>>> +     * streams. At least stdout and stderr (although the latter should be
>>> +     * non-buffered anyway) should be flushed, though. */
>>> +    fflush(stdout);
>>> +    fflush(stderr);
>>> +
>>> +    raise(sig);
>>> +    return 0;
>>> +}
>>> +
>>>   static void sleep_cb(void *opaque)
>>>   {
>>>       bool *expired = opaque;
>>> @@ -2202,4 +2247,5 @@ static void __attribute((constructor)) 
>>> init_qemuio_commands(void)
>>>       qemuio_add_command(&wait_break_cmd);
>>>       qemuio_add_command(&abort_cmd);
>>>       qemuio_add_command(&sleep_cmd);
>>> +    qemuio_add_command(&sigraise_cmd);
>>>   }
>> Looks good otherwise.
>
> Thanks :-)

Looking forward to v3 :)