Re: F_SETOWN_TID: F_SETOWN was thread-specific for a while

[stephane eranian]

On Mon, Aug 10, 2009 at 7:03 PM, Oleg Nesterov<oleg@xxxxxxxxxx> wrote:
> On 08/10, stephane eranian wrote:
>>
>> You must use F_SETSIG on SIGIO if you want your signal handler to
>> receive the file descriptor in siginfo. This is useful if you want to perform
>> some actions on the descriptor. That is the case in perfmon and this is
>> the case in certain situations with perfcounters as well.
>>
>> Setting SA_SIGINFO provides siginfo, but the si_fd field is NOT set
>> correctly without F_SETSIG. I have verified this with perfcounters, and
>> this is indeed the case.
>>
>> This behavior seems kind of odd to me.
>
> Agreed, this looks a bit odd. But at least this is documented. From
> man 2 fcntl:
>
> Â Â Â ÂBy using F_SETSIG with a nonzero value, and setting SA_SIGINFO for the
> Â Â Â Âsignal handler (see sigac- tion(2)), extra information about I/O events
> Â Â Â Âis passed to the handler in a Âsiginfo_t Âstructure. ÂIf Âthe si_code
> Â Â Â Âfield indicates the source is SI_SIGIO, the si_fd field gives the file
> Â Â Â Âdescriptor associated with the event. ÂOtherwise, there is no indication
> Â Â Â Âwhich file descriptors are pending,
>
> Not sure if it is safe to change the historical behaviour.
>
Don't need to change it.
But for SIGIO, if you see SA_SIGINFO, then pass the si_fd.
>From Jamie, it seems F_SETSIG was not added just for this file descriptor trick.
The initial goal seems orthogonal to the file descriptor passing in si_fd.

> (the manpage is not exactly right though, and the comment in send_sigio_to_task()
> Âis not right too: SI_SIGIO (and, btw, SI_QUEUE/SI_DETHREAD) is never used).
>
> Oleg.
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/