flag parameters: timerfd_create

The timerfd_create syscall already has a flags parameter.  It just is
unused so far.  This patch changes this by introducing the TFD_CLOEXEC
flag to set the close-on-exec flag for the returned file descriptor.

A new name TFD_CLOEXEC is introduced which in this implementation must
have the same value as O_CLOEXEC.

The following test must be adjusted for architectures other than x86 and
x86-64 and in case the syscall numbers changed.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
#include <fcntl.h>
#include <stdio.h>
#include <time.h>
#include <unistd.h>
#include <sys/syscall.h>

#ifndef __NR_timerfd_create
# ifdef __x86_64__
#  define __NR_timerfd_create 283
# elif defined __i386__
#  define __NR_timerfd_create 322
# else
#  error "need __NR_timerfd_create"
# endif
#endif

#define TFD_CLOEXEC O_CLOEXEC

int
main (void)
{
  int fd = syscall (__NR_timerfd_create, CLOCK_REALTIME, 0);
  if (fd == -1)
    {
      puts ("timerfd_create(0) failed");
      return 1;
    }
  int coe = fcntl (fd, F_GETFD);
  if (coe == -1)
    {
      puts ("fcntl failed");
      return 1;
    }
  if (coe & FD_CLOEXEC)
    {
      puts ("timerfd_create(0) set close-on-exec flag");
      return 1;
    }
  close (fd);

  fd = syscall (__NR_timerfd_create, CLOCK_REALTIME, TFD_CLOEXEC);
  if (fd == -1)
    {
      puts ("timerfd_create(TFD_CLOEXEC) failed");
      return 1;
    }
  coe = fcntl (fd, F_GETFD);
  if (coe == -1)
    {
      puts ("fcntl failed");
      return 1;
    }
  if ((coe & FD_CLOEXEC) == 0)
    {
      puts ("timerfd_create(TFD_CLOEXEC) set close-on-exec flag");
      return 1;
    }
  close (fd);

  puts ("OK");

  return 0;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/timerfd.c

@@ -184,7 +184,7 @@ asmlinkage long sys_timerfd_create(int clockid, int flags)
 	int ufd;
 	struct timerfd_ctx *ctx;
 
-	if (flags)
+	if (flags & ~TFD_CLOEXEC)
 		return -EINVAL;
 	if (clockid != CLOCK_MONOTONIC &&
 	    clockid != CLOCK_REALTIME)
@@ -198,7 +198,8 @@ asmlinkage long sys_timerfd_create(int clockid, int flags)
 	ctx->clockid = clockid;
 	hrtimer_init(&ctx->tmr, clockid, HRTIMER_MODE_ABS);
 
-	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx, 0);
+	ufd = anon_inode_getfd("[timerfd]", &timerfd_fops, ctx,
+			       flags & O_CLOEXEC);
 	if (ufd < 0)
 		kfree(ctx);
 

include/linux/timerfd.h

@@ -8,9 +8,14 @@
 #ifndef _LINUX_TIMERFD_H
 #define _LINUX_TIMERFD_H
 
+/* For O_CLOEXEC */
+#include <linux/fcntl.h>
 
+/* Flags for timerfd_settime.  */
 #define TFD_TIMER_ABSTIME (1 << 0)
 
+/* Flags for timerfd_create.  */
+#define TFD_CLOEXEC O_CLOEXEC
 
 
 #endif /* _LINUX_TIMERFD_H */