file watching + event ports = disaster

watch.c

/*
 * Copyright (c) 2011, Ben Noordhuis <info@bnoordhuis.nl>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <unistd.h>
#include <port.h>
#include <poll.h>

#define streq(a, b) (strcmp((a), (b)) == 0)

#define E(expr)             \
  do {                      \
    errno = 0;              \
    (expr);                 \
    if (errno) die(#expr);  \
  }                         \
  while (0)

static char *path = ".";
static int portfd = -1;
static port_event_t pe;
static struct file_obj fo;

static void die(const char *prefix)
{
  perror(prefix);
  exit(42);
}

static void rearm(void)
{
  if (portfd == -1) {
    fo.fo_name = path;
    E(portfd = port_create());
  }

  E(port_associate(portfd,
                   PORT_SOURCE_FILE,
                   (uintptr_t) &fo,
                   FILE_ACCESS|FILE_MODIFIED|FILE_ATTRIB,
                   fo.fo_name));
}

static void report(void)
{
  printf("events for '%s' -> %08x\n",
         (const char *) pe.portev_user,
         pe.portev_events);
}

static void receive_direct(void)
{
  E(port_get(portfd, &pe, NULL));
}

static void receive_port(void)
{
  int pfd;
  E(pfd = port_create());
  E(port_associate(pfd, PORT_SOURCE_FD, portfd, POLLIN, "outer poll"));
  E(port_get(pfd, &pe, NULL));
  report();
  receive_direct();
}

static void receive_poll(void)
{
  struct pollfd pfd;
  pfd.fd = portfd;
  pfd.events = POLLIN;
  pfd.revents = 0;
  E(poll(&pfd, 1, -1));
  printf("portfd events: %08x\n", pfd.revents);
  receive_direct();
}

int main(int argc, char **argv)
{
  void (*receive)(void) = receive_direct;

  if (argc > 1) {
    if (streq(argv[1], "--poll"))
      receive = receive_poll;
    else if (streq(argv[1], "--port"))
      receive = receive_port;
    else
      goto skip;
    argv++, argc--;
    skip: (void) 0;
  }

  if (argc > 1)
    path = argv[1];

  while (1) {
    rearm();
    receive();
    report();
  }

  return 0;
}