Attachment 216970 Details for Bug 248440 – test program to reproduce bug via filling/monitoring stdout

test program to reproduce bug via filling/monitoring stdout

kqwrite.c (text/plain), 1.71 KB, created by larkinconr on 2020-08-02 23:20:02 UTC

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Creator: larkinconr

Created: 2020-08-02 23:20:02 UTC

Size: 1.71 KB

patch

obsolete

>#include <sys/event.h>
>#include <sys/stat.h>
>#include <string.h>
>#include <unistd.h>
>#include <fcntl.h>
>#include <errno.h>
>#include <stdio.h>
>#include <err.h>
>#include <sysexits.h>
>#include <signal.h>
>
>int main(void)
>{
>  // Check up front that stdout is a pipe. Otherwise we're going to
>  // spew to the terminal or use up someone's disk.
>  struct stat stat_buf;
>  if ( fstat(1, &stat_buf) ) {
>    err(EX_OSERR, "fstat");
>  }
>  if ( (stat_buf.st_mode & S_IFMT) != S_IFIFO ) {
>    errx(EX_USAGE, "stdout is not a pipe");
>  }
>
>  // ignore SIGPIPE; set stdout nonblocking
>  signal(SIGPIPE, SIG_IGN);
>  int flags = fcntl(1, F_GETFL);
>  if ( flags < 0 ) {
>    err(EX_OSERR, "fcntl(F_GETFL)");
>  }
>  if ( fcntl(1, F_SETFL, flags | O_NONBLOCK) ) {
>    err(EX_OSERR, "fcntl(F_SETFL)");
>  }
>
>  // Attempt to fill up the pipe that is stdout.
>  char buf[4096];
>  memset(buf, 'a', sizeof(buf));
>  int got_eagain = 0;
>  do {
>    ssize_t nwritten = write(1, buf, sizeof(buf));
>    if ( nwritten < 0 ) {
>      if ( errno == EAGAIN ) {
>        got_eagain = 1;
>      } else {
>        err(EX_OSERR, "write");
>      }
>    }
>  } while ( !got_eagain );
>
>  // wait for something interesting to happen on stdout.
>  int kq = kqueue();
>  if ( kq < 0 ) {
>    errx(EX_OSERR, "kevent");
>  }
>  struct kevent kev;
>  EV_SET(&kev, 1, EVFILT_WRITE, EV_ADD | EV_ENABLE, 0, 0, NULL);
>  struct kevent result = { 0 };
>  int wait_result = kevent(kq, &kev, 1, &result, 1, NULL);
>  fprintf(stderr, "kevent returned %d\n", wait_result);
>  if ( wait_result > 0 ) {
>    fprintf(stderr, "\t%llu %d %d %d %lld %p\n", (unsigned long long)result.ident,
>            (int)result.filter, (int)result.flags, (int)result.fflags,
>            (long long)result.data, result.udata);
>  }
>  return 0;
>}

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Attachments on bug 248440: 216970