procps: add support for linux namespaces

Each process in Linux has a /proc/<pid>/ns directory which contains
symbolic links to pipes that identify which namespaces that process
belongs to. This patch adds support for ps to display that information
optionally.

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>

proc/readproc.h

@@ -31,6 +31,18 @@ EXTERN_C_BEGIN
 // neither tgid nor tid seemed correct. (in other words, FIXME)
 #define XXXID tid
 
+#define NUM_NS 6
+enum ns_type {
+    IPCNS = 0,
+    MNTNS,
+    NETNS,
+    PIDNS,
+    USERNS,
+    UTSNS
+};
+extern const char *get_ns_name(int id);
+extern int get_ns_id(const char *name);
+
 // Basic data structure which holds all information we can get about a process.
 // (unless otherwise specified, fields are read from /proc/#/stat)
 //
@@ -157,6 +169,8 @@ typedef struct proc_t {
         oom_score,      // oom_score       (badness for OOM killer)
         oom_adj;        // oom_adj         (adjustment to OOM score)
 #endif
+    ino_t
+        ns[NUM_NS];     // ns/*            inode number of /proc/<pid>/ns/*
 } proc_t;
 
 // PROCTAB: data structure holding the persistent information readproc needs
@@ -266,6 +280,7 @@ extern proc_t * get_proc_stats(pid_t pid, proc_t *p);
 #define PROC_FILLCGROUP      0x0200 // alloc and fill in `cgroup`
 #define PROC_FILLSUPGRP      0x0400 // resolve supplementary group id -> group name
 #define PROC_FILLOOM         0x0800 // fill in proc_t oom_score and oom_adj
+#define PROC_FILLNS          0x8000 // fill in proc_t namespace information
 
 #define PROC_LOOSE_TASKS     0x2000 // treat threads as if they were processes