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, 4 insertions, 0 deletions

diff --git a/sys/kern/syscalls.master b/sys/kern/syscalls.master
index 4b3348f83e31..922db305f049 100644
--- a/sys/kern/syscalls.master
+++ b/sys/kern/syscalls.master
@@ -972,5 +972,9 @@
 				    int namelen); }
 540	AUE_CHFLAGSAT	STD	{ int chflagsat(int fd, const char *path, \
 				    u_long flags, int atflag); }
+541	AUE_ACCEPT	STD	{ int accept4(int s, \
+				    struct sockaddr * __restrict name, \
+				    __socklen_t * __restrict anamelen, \
+				    int flags); }
 ; Please copy any additions and changes to the following compatability tables:
 ; sys/compat/freebsd32/syscalls.master