flag parameters: NONBLOCK in signalfd

This patch adds support for the SFD_NONBLOCK flag to signalfd4. The
additional changes needed are minimal.

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 <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>

#ifndef __NR_signalfd4
# ifdef __x86_64__
# define __NR_signalfd4 289
# elif defined __i386__
# define __NR_signalfd4 327
# else
# error "need __NR_signalfd4"
# endif
#endif

#define SFD_NONBLOCK O_NONBLOCK

int
main (void)
{
sigset_t ss;
sigemptyset (&ss);
sigaddset (&ss, SIGUSR1);
int fd = syscall (__NR_signalfd4, -1, &ss, 8, 0);
if (fd == -1)
{
puts ("signalfd4(0) failed");
return 1;
}
int fl = fcntl (fd, F_GETFL);
if (fl == -1)
{
puts ("fcntl failed");
return 1;
}
if (fl & O_NONBLOCK)
{
puts ("signalfd4(0) set non-blocking mode");
return 1;
}
close (fd);

fd = syscall (__NR_signalfd4, -1, &ss, 8, SFD_NONBLOCK);
if (fd == -1)
{
puts ("signalfd4(SFD_NONBLOCK) failed");
return 1;
}
fl = fcntl (fd, F_GETFL);
if (fl == -1)
{
puts ("fcntl failed");
return 1;
}
if ((fl & O_NONBLOCK) == 0)
{
puts ("signalfd4(SFD_NONBLOCK) does not set non-blocking mode");
return 1;
}
close (fd);

puts ("OK");

return 0;
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Ulrich Drepper <[e-mail]>
Acked-by: Davide Libenzi <[e-mail]>
Cc: Michael Kerrisk <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/signalfd.c

···
 	sigset_t sigmask;
 	struct signalfd_ctx *ctx;
 
-	if (flags & ~SFD_CLOEXEC)
+	if (flags & ~(SFD_CLOEXEC | SFD_NONBLOCK))
 		return -EINVAL;
 
 	if (sizemask != sizeof(sigset_t) ||
···
 		 * anon_inode_getfd() will install the fd.
 		 */
 		ufd = anon_inode_getfd("[signalfd]", &signalfd_fops, ctx,
-				       flags & O_CLOEXEC);
+				       flags & (O_CLOEXEC | O_NONBLOCK));
 		if (ufd < 0)
 			kfree(ctx);
 	} else {

include/linux/signalfd.h

···
 #ifndef _LINUX_SIGNALFD_H
 #define _LINUX_SIGNALFD_H
 
-/* For O_CLOEXEC */
+/* For O_CLOEXEC and O_NONBLOCK */
 #include <linux/fcntl.h>
 
 /* Flags for signalfd4.  */
 #define SFD_CLOEXEC O_CLOEXEC
+#define SFD_NONBLOCK O_NONBLOCK
 
 struct signalfd_siginfo {
 	__u32 ssi_signo;