On Sat, Jan 19, 2013 at 1:36 AM, horseriver <horserivers@xxxxxxxxx> wrote:
On Fri, Jan 18, 2013 at 10:18:19AM +0800, Peter Teoh wrote:Thanks!
> 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.
>
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:
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>
>
>
> --
> Regards,
> Peter Teoh
Regards,
Peter Teoh
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