How to wake_up the wait_queue of a socket?

[Peter Teoh]

On Sat, Jan 19, 2013 at 1:36 AM, horseriver <horserivers at gmail.com> wrote:

> On Fri, Jan 18, 2013 at 10:18:19AM +0800, Peter Teoh wrote:
> > essentially, when the packet arrive, it will be assigned to the correct
> > process based on IP address + port matching, and then the corresponding
> > process's blocked scheduling status will be changed to continue
> execution,
> > so that when the scheduler next selection of runnable process will pick
> him
> > out for continue execution.   The process will then pick his data up from
> > the network queue.
> >
>
>   Thanks!
>
>   If there is no event occured on one socket descriptor  ,
>   will the poll operation on this socket descriptor be blocked ?
>

I/O mechanism have two types:  blocking and non-blocking.   by definition:
poll is non-blocking, and select() is blocking.  In general that is true
for kernel source as well.

For details and implementations there may be ambiguity.

For eg, manpage say poll may has a timeout for blocking, and inside the
kernel source:

in fs/select.c's definition for select() syscall:

SYSCALL_DEFINE5(select, int, n, fd_set __user *, inp, fd_set __user *, outp,
                fd_set __user *, exp, struct timeval __user *, tvp)
{
        struct timespec end_time, *to = NULL;
        struct timeval tv;
        int ret;

        if (tvp) {
                if (copy_from_user(&tv, tvp, sizeof(tv)))
                        return -EFAULT;

                to = &end_time;
                if (poll_select_set_timeout(to,
                                tv.tv_sec + (tv.tv_usec / USEC_PER_SEC),
                                (tv.tv_usec % USEC_PER_SEC) *
NSEC_PER_USEC))
                        return -EINVAL;
        }

        ret = core_sys_select(n, inp, outp, exp, to);
        ret = poll_select_copy_remaining(&end_time, tvp, 1, ret);


And for syscall of poll() (same file):

SYSCALL_DEFINE3(poll, struct pollfd __user *, ufds, unsigned int, nfds,
                long, timeout_msecs)
{
        struct timespec end_time, *to = NULL;
        int ret;

        if (timeout_msecs >= 0) {
                to = &end_time;
                poll_select_set_timeout(to, timeout_msecs / MSEC_PER_SEC,
                        NSEC_PER_MSEC * (timeout_msecs % MSEC_PER_SEC));
        }

So there is this common file poll_select_set_timeout() called by
both....the details is even more confusing - shall stop here.

A good article on epoll etc:

http://www.eecs.berkeley.edu/~sangjin/2012/12/21/epoll-vs-kqueue.html



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> >
> >
> >
> > --
> > Regards,
> > Peter Teoh
>



-- 
Regards,
Peter Teoh
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