flua: add freebsd.kenv, kenv(2) bindings

Add bindings for kenv(2) right now only get() has been created
it allows do dump into a key/value table the kernel environement if
no argument is passed, or it returns the value associated to the
provided key.

Reviewed by:	imp, kevans, markj
Accepted by:	imp, kevans
Differential Revision:	https://reviews.freebsd.org/D46654

libexec/flua/libfreebsd/Makefile

@@ -1,3 +1,4 @@
+SUBDIR+=	kenv
 SUBDIR+=	sys
 
 .include <bsd.subdir.mk>

libexec/flua/libfreebsd/Makefile.inc

@@ -1 +1,3 @@
+SHLIBDIR?=	${LIBDIR}/flua/freebsd
+
 .include "../Makefile.inc"

libexec/flua/libfreebsd/kenv/Makefile

@@ -0,0 +1,5 @@
+SHLIB_NAME=	kenv.so
+SRCS+=		kenv.c
+MAN=		freebsd.kenv.3lua
+
+.include <bsd.lib.mk>

libexec/flua/libfreebsd/kenv/freebsd.kenv.3lua

@@ -0,0 +1,44 @@
+.\"
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
+.\" Copyright (c) 2024, Baptiste Daroussin <bapt@FreeBSD.org>
+.\"
+.Dd September 6, 2024
+.Dt FREEBSD.KENV 3lua
+.Os
+.Sh NAME
+.Nm freebsd.kenv
+.Nd Lua binding to
+.Fx 's
+Linker functions
+.Sh SYNOPSIS
+.Bd -literal
+local kenv = require('freebsd.kenv')
+.Ed
+.Pp
+.Bl -tag -width XXXX -compact
+.It Dv table = kenv.get()
+.It Dv value = kenv.get(key)
+.El
+.Sh DESCRIPTION
+The
+.Nm
+module is a binding to the
+.Xr kenv 2
+function.
+.Pp
+List of functions:
+.Bl -tag -width XXXX
+.It Dv table = freebsd.kenv.get()
+Dump the kernel environnement into a key/value
+.Fa table .
+.It Dv value = freebsd.kenv.get(key)
+Return the
+.Fa value
+associated to the
+.Fa key ,
+if it exists, or
+.Va nil
+otherwise.
+.Sh SEE ALSO
+.Xr kenv 2

libexec/flua/libfreebsd/kenv/kenv.c

@@ -0,0 +1,96 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2024, Baptiste Daroussin <bapt@FreeBSD.org>
+ */
+
+#include <errno.h>
+#include <kenv.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <lua.h>
+#include <lualib.h>
+#include <lauxlib.h>
+
+int luaopen_freebsd_kenv(lua_State *L);
+
+static int
+lua_kenv_get(lua_State *L)
+{
+	const char *env;
+	int ret, n;
+	char value[1024];
+
+	n = lua_gettop(L);
+	if (n == 0) {
+		char *buf, *bp, *cp;
+		int size;
+
+		size = kenv(KENV_DUMP, NULL, NULL, 0);
+		if (size < 0) {
+			lua_pushnil(L);
+			lua_pushstring(L, strerror(errno));
+			lua_pushinteger(L, errno);
+			return (3);
+		}
+		size += 1;
+		buf = malloc(size);
+		if (buf == NULL) {
+			lua_pushnil(L);
+			lua_pushstring(L, strerror(errno));
+			lua_pushinteger(L, errno);
+			return (3);
+		}
+		if (kenv(KENV_DUMP, NULL, buf, size) < 0) {
+			free(buf);
+			lua_pushnil(L);
+			lua_pushstring(L, strerror(errno));
+			lua_pushinteger(L, errno);
+			return (3);
+		}
+
+		lua_newtable(L);
+		for (bp = buf; *bp != '\0'; bp += strlen(bp) + 1) {
+			cp = strchr(bp, '=');
+			if (cp == NULL)
+				continue;
+			*cp++ = '\0';
+			lua_pushstring(L, cp);
+			lua_setfield(L, -2, bp);
+			bp = cp;
+		}
+		free(buf);
+		return (1);
+	}
+	env = luaL_checkstring(L, 1);
+	ret = kenv(KENV_GET, env, value, sizeof(value));
+	if (ret == -1) {
+		if (errno == ENOENT) {
+			lua_pushnil(L);
+			return (1);
+		}
+		lua_pushnil(L);
+		lua_pushstring(L, strerror(errno));
+		lua_pushinteger(L, errno);
+		return (3);
+	}
+	lua_pushstring(L, value);
+	return (1);
+}
+
+#define REG_SIMPLE(n)	{ #n, lua_kenv_ ## n }
+static const struct luaL_Reg freebsd_kenv[] = {
+	REG_SIMPLE(get),
+	{ NULL, NULL },
+};
+#undef REG_SIMPLE
+
+int
+luaopen_freebsd_kenv(lua_State *L)
+{
+	luaL_newlib(L, freebsd_kenv);
+
+	return (1);
+}