select()

[Marcus Brinkmann]

Hi,

I tried to debug the apt-get/select() situation, but I have to admit
I am totally and completely confused.  What happens doesn't make any sense
to me.

I set a break point at hurdselect.c:320, where an EINTR response from pfinet
is handled.  At this point:

Breakpoint 1, _hurd_select (nfds=5, pollfds=0x0, readfds=0x1025a9c,
    writefds=0x1025a7c, exceptfds=0x0, timeout=0x1025a24, sigmask=0x0)
    at hurdselect.c:320
320                       err = EINTR;
(gdb) print msgerr
$5 = EINTR
(gdb) print msg
$6 = {head = {msgh_bits = 4352, msgh_size = 32, msgh_remote_port = 0,
    msgh_local_port = 51, msgh_seqno = 0, msgh_id = 21112}, error = {head = {
      msgh_bits = 4352, msgh_size = 32, msgh_remote_port = 0,
      msgh_local_port = 51, msgh_seqno = 0, msgh_id = 21112}, err_type = {
      msgt_name = 2, msgt_size = 32, msgt_number = 1, msgt_inline = 1,
      msgt_longform = 0, msgt_deallocate = 0, msgt_unused = 0}, err = EINTR},
  success = {head = {msgh_bits = 4352, msgh_size = 32, msgh_remote_port = 0,
      msgh_local_port = 51, msgh_seqno = 0, msgh_id = 21112}, err_type = {
      msgt_name = 2, msgt_size = 32, msgt_number = 1, msgt_inline = 1,
      msgt_longform = 0, msgt_deallocate = 0, msgt_unused = 0}, err = EINTR,
    result_type = {msgt_name = 197, msgt_size = 196, msgt_number = 2861,
      msgt_inline = 0,, msgt_longform = 0, msgt_deallocate = 0,
      msgt_unused = 1}, result = -983697778}}
(gdb)

This is not possible!!! msgerr can not be EINTR at this point, otherwise
the while() loop should have been terminated!

(gdb) print *timeout
$7 = {tv_sec = 120, tv_nsec = 0}
(gdb) print options
$8 = 256

The rest is only consequent breakage:
(gdb) n
321                       goto poll;
(gdb)
358                   to = 0;
(gdb)
359                   options |= MACH_RCV_TIMEOUT;
(gdb)
361             }
(gdb)
363           if (err == MACH_RCV_TIMED_OUT)
(gdb)

>From there, it returns EINTR to the caller.

Another question is why pfinet returns EINTR.  It seems to happen if I have two
connections, eg, I am downloading with apt-get, and then start lynx with a
page.  This quickly and reproducably leads to an EINTR from pfinet.  Is
this correct behaviour?  What does interrupting mean for pfinet?

Oh, and a timeout of 0 doesn't work anyway, as we found out earlier.  Should
this code be changed to use the minimal timeout?

Thanks,
Marcus