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Date: Tue, 25 Jun 2002 11:30:52 -0500
From: Amos Waterland <apw@us.ibm.com>
To: linux-kernel@vger.kernel.org
Subject: O_ASYNC question
Message-ID: <20020625113052.A7510@kvasir.austin.ibm.com>
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The man page for fcntl() says:

    If you set the O_ASYNC status flag on a file descriptor (either by
    providing this flag with the open(2) call, or by using the F_SETFL
    command of fcntl), a SIGIO signal is sent whenever input or output
    becomes possible on that file descriptor.

On a 2.4.18 kernel, this test program waits forever in sigwaitinfo():

    #include <fcntl.h>
    #include <signal.h>
    #include <stdio.h>
    #include <stdlib.h>
    #include <unistd.h>

    int main(int argc, char *argv[])
    {
      const int BYTES = 5000000;
      int i, fd;
      char buff[BYTES];
      char name[] = "/tmp/aio8.XXXXXX";
      sigset_t sigset;
      siginfo_t siginfo;

      if ((fd = open(name, O_CREAT|O_WRONLY|O_NONBLOCK|O_ASYNC, 0600)) < 0 ||
          unlink(name)) {
        perror("creating temp file"); exit(1);
      }

      for (i = 0; i < BYTES; i++) buff[i] = 'Z';

      if (sigemptyset(&sigset) || sigaddset(&sigset, SIGIO) ||
          sigprocmask(SIG_BLOCK, &sigset, NULL)) {
        perror("setting up signal mask"); exit(2);
      }

      if (write(fd, buff, BYTES) < 0) {
        perror("writing to temp file"); exit(3);
      }

      printf("recv sig: %i\n", sigwaitinfo(&sigset, &siginfo));

      return 0;
    }

Shouldn't SIGIO be raised when the write() completes?  (Is O_ASYNC only
valid for sockets, maybe?)  Thanks in advance.

Amos Waterland