util-linux: Add an option to compile 'nsenter' binary.

nsenter is a tool to enter the namespace of another process.

[Thomas: add dependency to 3.0 kernel headers, since the setns()
system call was added in Linux 3.0.]

Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/util-linux/Config.in

@@ -118,6 +118,15 @@ config BR2_PACKAGE_UTIL_LINUX_MESG
 	help
 	  Control write access to your terminal
 
+config BR2_PACKAGE_UTIL_LINUX_NSENTER
+	bool "nsenter"
+	depends on BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_0
+	help
+	  Enter the namespaces of another process.
+
+comment "nsenter needs a toolchain w/ headers >= 3.0"
+	depends on !BR2_TOOLCHAIN_HEADERS_AT_LEAST_3_0
+
 config BR2_PACKAGE_UTIL_LINUX_MOUNT
 	bool "mount/umount"
 	help

package/util-linux/util-linux.mk

@@ -74,6 +74,7 @@ UTIL_LINUX_CONF_OPTS += \
 	$(if $(BR2_PACKAGE_UTIL_LINUX_LOGIN_UTILS),--enable-last --enable-login --enable-su --enable-sulogin,--disable-last --disable-login --disable-su --disable-sulogin) \
 	$(if $(BR2_PACKAGE_UTIL_LINUX_LOSETUP),--enable-losetup,--disable-losetup) \
 	$(if $(BR2_PACKAGE_UTIL_LINUX_MESG),--enable-mesg,--disable-mesg) \
+	$(if $(BR2_PACKAGE_UTIL_LINUX_NSENTER),--enable-nsenter,--disable-nsenter) \
 	$(if $(BR2_PACKAGE_UTIL_LINUX_MOUNT),--enable-mount,--disable-mount) \
 	$(if $(BR2_PACKAGE_UTIL_LINUX_NEWGRP),--enable-newgrp,--disable-newgrp) \
 	$(if $(BR2_PACKAGE_UTIL_LINUX_PARTX),--enable-partx,--disable-partx) \