configure: add checks for user namespace capabilities

Add tests for:
  * ns_capable
  * user_ns in cred_t
  * kuid/kgid_has_mapping()

Signed-off-by: Wolfgang Bumiller <[email protected]>

config/kernel-userns-capabilities.m4

@@ -0,0 +1,67 @@
+dnl #
+dnl # 2.6.38 API change
+dnl # ns_capable() was introduced
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_NS_CAPABLE], [
+	AC_MSG_CHECKING([whether ns_capable exists])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/capability.h>
+	],[
+		ns_capable((struct user_namespace *)NULL, CAP_SYS_ADMIN);
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_NS_CAPABLE, 1,
+		    [ns_capable exists])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+dnl #
+dnl # 2.6.39 API change
+dnl # struct user_namespace was added to struct cred_t as
+dnl # cred->user_ns member
+dnl # Note that current_user_ns() was added in 2.6.28.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_CRED_USER_NS], [
+	AC_MSG_CHECKING([whether cred_t->user_ns exists])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/cred.h>
+	],[
+		struct cred cr;
+		cr.user_ns = (struct user_namespace *)NULL;
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_CRED_USER_NS, 1,
+		    [cred_t->user_ns exists])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+dnl #
+dnl # 3.4 API change
+dnl # kuid_has_mapping() and kgid_has_mapping() were added to distinguish
+dnl # between internal kernel uids/gids and user namespace uids/gids.
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_KUID_HAS_MAPPING], [
+	AC_MSG_CHECKING([whether kuid_has_mapping/kgid_has_mapping exist])
+	ZFS_LINUX_TRY_COMPILE([
+		#include <linux/uidgid.h>
+	],[
+		kuid_has_mapping((struct user_namespace *)NULL, KUIDT_INIT(0));
+		kgid_has_mapping((struct user_namespace *)NULL, KGIDT_INIT(0));
+	],[
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_KUID_HAS_MAPPING, 1,
+		    [kuid_has_mapping/kgid_has_mapping exist])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_USERNS_CAPABILITIES], [
+	ZFS_AC_KERNEL_NS_CAPABLE
+	ZFS_AC_KERNEL_CRED_USER_NS
+	ZFS_AC_KERNEL_KUID_HAS_MAPPING
+])

config/kernel.m4

@@ -125,6 +125,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
 	ZFS_AC_KERNEL_CURRENT_TIME
 	ZFS_AC_KERNEL_GLOBAL_PAGE_STATE
 	ZFS_AC_KERNEL_ACL_HAS_REFCOUNT
+	ZFS_AC_KERNEL_USERNS_CAPABILITIES
 
 	AS_IF([test "$LINUX_OBJ" != "$LINUX"], [
 		KERNEL_MAKE="$KERNEL_MAKE O=$LINUX_OBJ"