Re: [PATCH,HURD][RFC] hurdselect: Step7x, almost complete rewrite finished

[Svante Signell]

On Tue, 2013-02-12 at 22:55 +0100, Samuel Thibault wrote:
> Svante Signell, le Tue 12 Feb 2013 09:09:25 +0100, a écrit :
> > Attached is a patch wrt the latest patch (step2) on January 24 2013. The
> > indentation is different, therefore the diff blocks are a little large
> > (but easier to read). Hopefully this is better. Including also the
> > resulting file hurdselect_step7x.c. Explanations later in a separate
> > mail.
> 
> Explanations don't need to be very long. All we need is the rationale
> and the way you handle it in the patch.
> 
> AIUI, there are three things:
> 
> - pass 1ms as timeout. This will be fixed by Richard's patch.
> - in the poll() case, do not fail completely if an FD is bogus. Instead,
>   poll on the remaining FDs, and later on set POLLNVAL. It seems your
>   patch does this by using the i_index array indirection.
> - in the poll() case, on error returned by io_select, instead of setting
>   readiness, set POLLHUP or POLLERR according to the error.
> 
> Is that right?

Yes, mainly.

Here it goes:
- introduce the dfd struct, to be instantiated later in _hurd_select()
- introduce two helper functions, _io_select_request() and _wait_for
replies()

- in _io_select_request():
  * this function calls __io_select()
  * store the errors EPIPE and EPOLL for poll in errvec[nfds] to fill in
the revents field of the struct pollfd later. 
 * return with value -1 for other errors.
 * add a delay of 1ms in the call to __io_select() for POLL to account
for the round-trip delay (will be fixed by the changes by Richard to
move time-outs to the server)

- in _wait_for_replies():
  * move all union and MDGID definitions here, since they are local to
this routine.
 * this function calls __mach_msg()

- in _hurd_select():
 * split the code into two cases: POLL and SELECT
 * change the FD_SETSIZE upper value check to larger than or equal from
larger than.
(from POSIX definition of select:
http://pubs.opengroup.org/onlinepubs/009604499/functions/select.html
)
 * call the helper functions for both cases.

- for the POLL case:
   * mark all FDs in i_index[nfds] with -1 to start.
  * fill in the corresponding revents according to if the FDs are: good,
broken (EPIPE or EIO) or bad i_index[] = -1.
 * fix a bug causing test_poll in python2.6 to fail: Clear out all
revents fields before fiilng in. The caller might have set the fd and
events correctly with crap in the revents field.
 * remove the i < nfds check, it is redundant since all nfds FDs are
walked through.

- for the SELECT case
 * exit with EBADF if nfds are larger than _hurd_dtablesize (fixes one
test case in test-select from gnulib.

- the POLL changes works with the Hurd built on January 28, see test
code to be sent in a forthcoming mail.
- some minor tweaks will still be made to be mor POSIX consistent.

Svante