Re: [PATCH RFC 0/6] epoll: Introduce new syscall "epoll_mod_wait"

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 01/20/2015 11:40 PM, Andy Lutomirski wrote:
> On Tue, Jan 20, 2015 at 1:57 AM, Fam Zheng <famz-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>> This adds a new system call, epoll_mod_wait. It's described as below:

[...]

>>        There is no guartantee that all the commands are executed in order. Only
>>        if all the commands are successfully executed (all the error fields are
>>        set to 0), events are polled.
> 
> If this doesn't happen, what error is returned?

If I read the code correctly: the error of the first epoll_ctl op that fails.

[...]

>> RETURN VALUE
>>
>>        When any error occurs, epoll_mod_wait() returns -1 and errno is set
>>        appropriately. All the "error" fields in cmds are unchanged before they
>>        are executed, and if any cmds are executed, the "error" fields are set
>>        to a return code accordingly. See also epoll_ctl for more details of the
>>        return code.
> 
> Does this mean that callers should initialize the error fields to an
> impossible value first so they can tell which commands were executed?

Yes. (Ugly!)

[...]

>> ERRORS
>>
>>        These errors apply on either the return value of epoll_mod_wait or error
>>        status for each command, respectively.
> 
> Please clarify which errors are returned overall and which are per-command.

Yes, I think this would be valuable as well.

Thanks,

Michael

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/