Add accept4() system call.

The accept4() function, compared to accept(), allows setting the new file
descriptor atomically close-on-exec and explicitly controlling the
non-blocking status on the new socket. (Note that the latter point means
that accept() is not equivalent to any form of accept4().)

The linuxulator's accept4 implementation leaves a race window where the new
file descriptor is not close-on-exec because it calls sys_accept(). This
implementation leaves no such race window (by using falloc() flags). The
linuxulator could be fixed and simplified by using the new code.

Like accept(), accept4() is async-signal-safe, a cancellation point and
permitted in capability mode.

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/sys/syscallsubr.h b/sys/sys/syscallsubr.h
index fa0d351..49e8be1 100644
--- a/sys/sys/syscallsubr.h
+++ b/sys/sys/syscallsubr.h
@@ -60,6 +60,8 @@ int	kern___getcwd(struct thread *td, u_char *buf, enum uio_seg bufseg,
 	    u_int buflen);
 int	kern_accept(struct thread *td, int s, struct sockaddr **name,
 	    socklen_t *namelen, struct file **fp);
+int	kern_accept4(struct thread *td, int s, struct sockaddr **name,
+	    socklen_t *namelen, int flags, struct file **fp);
 int	kern_access(struct thread *td, char *path, enum uio_seg pathseg,
 	    int flags);
 int	kern_accessat(struct thread *td, int fd, char *path,