library: rework namespace calls

Functions related to namespaces were half-in half-out of the
procps library and didn't fit the standard naming scheme.

While struct { long ns[x]} is a bit clunky, its the only way
to "lock in" x. The alternative is to use ns_* variables.

This work was needed before pgrep could be converted.

proc/namespace.h

@@ -0,0 +1,51 @@
+/*
+ * libprocps - Library to read proc filesystem
+ *
+ * Copyright (C) 1996 Charles Blake <cblake@bbn.com>
+ * Copyright (C) 1998 Michael K. Johnson
+ * Copyright (C) 1998-2003 Albert Cahalan
+ * Copyright (C) 2015 Craig Small <csmall@enc.com.au>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+#ifndef PROC_NAMESPACE_H
+#define PROC_NAMESPACE_H
+
+#include <proc/procps.h>
+
+__BEGIN_DECLS
+
+enum namespace_type {
+    PROCPS_NS_IPC,
+    PROCPS_NS_MNT,
+    PROCPS_NS_NET,
+    PROCPS_NS_PID,
+    PROCPS_NS_USER,
+    PROCPS_NS_UTS,
+    PROCPS_NS_COUNT  // total namespaces (fencepost)
+};
+
+struct procps_namespaces {
+    long ns[PROCPS_NS_COUNT];
+};
+
+const char *procps_ns_get_name(const int id);
+
+int procps_ns_get_id(const char *name);
+
+int procps_ns_read_pid(const int pid, struct procps_namespaces *nsp);
+__END_DECLS
+
+#endif