From 19fe0d9ae12644b8af9513aa2a8cf7d16f7caa61 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Fri, 4 Mar 2016 16:40:30 -0500
Subject: [PATCH] Add posix.redirect2null

This is useful to silence output in forked programs:
https://bugzilla.redhat.com/show_bug.cgi?id=1287918

Tested with the following scriptlet:
%post -p <lua>
pid = posix.fork()
if pid == 0 then
    assert(posix.exec("/bin/sed"))
elseif pid > 0 then
    posix.wait(pid)
end
pid = posix.fork()
if pid == 0 then
    posix.redirect2null(2)
    assert(posix.exec("/bin/awk"))
elseif pid > 0 then
    posix.wait(pid)
end

As expected, the error message from sed is printed, the error message
from awk is not.
---
 luaext/lposix.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/luaext/lposix.c b/luaext/lposix.c
index 51ea2b3..c578c5a 100644
--- a/luaext/lposix.c
+++ b/luaext/lposix.c
@@ -819,6 +819,25 @@ static int Pmkstemp(lua_State *L)
 	return 2;
 }
 
+static int Predirect2null(lua_State *L)
+{
+    int target_fd, fd, r, e;
+
+    if (!have_forked)
+	return luaL_error(L, "silence_file_descriptor not permitted in this context");
+
+    target_fd = luaL_checkinteger(L, 1);
+
+    r = fd = open("/dev/null", O_WRONLY);
+    if (fd >= 0 && fd != target_fd) {
+	r = dup2(fd, target_fd);
+	e = errno;
+	(void) close(fd);
+	errno = e;
+    }
+    return pushresult(L, r, NULL);
+}
+
 static const luaL_Reg R[] =
 {
 	{"access",		Paccess},
@@ -861,6 +880,7 @@ static const luaL_Reg R[] =
 	{"wait",		Pwait},
 	{"setenv",		Psetenv},
 	{"unsetenv",		Punsetenv},
+	{"redirect2null",       Predirect2null},
 	{NULL,			NULL}
 };
 
-- 
1.9.3