[PATCH v8 1/2] procfs: show hierarchy of pid namespace

[Chen Hanxiao]

We lack of pid hierarchy information, and this will lead to:
a) we don't know pids' relationship, who is whose child:
   /proc/PID/ns/pid only tell us whether two pids live in different ns
b) bring trouble to nested lxc container check/restore/migration
c) bring trouble to pid translation between containers;

This patch will show the hierarchy of pid namespace
by pidns_hierarchy like:

<init_PID> <parent_of_init_PID> <relative PID level>

Ex:
[root@localhost ~]#cat /proc/pidns_hierarchy
18060 1 1
18102 18060 2
1534  18102 3
1600  18102 3
1550  1 1
*Note: numbers represent the pid 1 in different ns

It shows the pid hierarchy below:

      init_pid_ns 1
              â
ââââââââââââââ
ns1                      ns2
â                        â
1550                    18060
                          â
                          â
                         ns3
                          â
                        18102
                          â
                 ââââââââââââ
                 ns4                   ns5
                 â                    â
                1534                  1600

Every pid printed in pidns_hierarchy
is the init pid of that pid ns level.

Signed-off-by: Chen Hanxiao <chenhanxiao@xxxxxxxxxxxxxx>
---
v8: fix some improper comments
    use max() from kernel.h
v7: change stype to be consistent with current interface like
    <init_PID> <parent_of_init_PID> <relative PID level>
    remove EXPERT dependent in Kconfig
v6: fix a get_pid leak and do some cleanups;
v5: collect pid by find_ge_pid;
    use local list inside nslist_proc_show;
    use get_pid, remove mutex lock.
v4: simplify pid collection and some performance optimizamtion
    fix another race issue.
v3: fix a race issue and memory leak issue
v2: use a procfs text file instead of dirs under /proc

 fs/proc/Kconfig           |   6 +
 fs/proc/Makefile          |   1 +
 fs/proc/pidns_hierarchy.c | 280 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 287 insertions(+)
 create mode 100644 fs/proc/pidns_hierarchy.c

diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
index 2183fcf..82dda55 100644
--- a/fs/proc/Kconfig
+++ b/fs/proc/Kconfig
@@ -71,3 +71,9 @@ config PROC_PAGE_MONITOR
 	  /proc/pid/smaps, /proc/pid/clear_refs, /proc/pid/pagemap,
 	  /proc/kpagecount, and /proc/kpageflags. Disabling these
           interfaces will reduce the size of the kernel by approximately 4kb.
+
+config PROC_PID_HIERARCHY
+	bool "Enable /proc/pidns_hierarchy support"
+	depends on PROC_FS
+	help
+	  Show pid namespace hierarchy information
diff --git a/fs/proc/Makefile b/fs/proc/Makefile
index 7151ea4..33e384b 100644
--- a/fs/proc/Makefile
+++ b/fs/proc/Makefile
@@ -30,3 +30,4 @@ proc-$(CONFIG_PROC_KCORE)	+= kcore.o
 proc-$(CONFIG_PROC_VMCORE)	+= vmcore.o
 proc-$(CONFIG_PRINTK)	+= kmsg.o
 proc-$(CONFIG_PROC_PAGE_MONITOR)	+= page.o
+proc-$(CONFIG_PROC_PID_HIERARCHY)	+= pidns_hierarchy.o
diff --git a/fs/proc/pidns_hierarchy.c b/fs/proc/pidns_hierarchy.c
new file mode 100644
index 0000000..057d748
--- /dev/null
+++ b/fs/proc/pidns_hierarchy.c
@@ -0,0 +1,280 @@
+#include <linux/init.h>
+#include <linux/errno.h>
+#include <linux/proc_fs.h>
+#include <linux/module.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+#include <linux/pid_namespace.h>
+#include <linux/seq_file.h>
+#include <linux/kernel.h>
+
+/*
+ *  /proc/pidns_hierarchy
+ *
+ *  show the hierarchy of pid namespace as:
+ *  <init_PID> <parent_of_init_PID> <relative PID level>
+ *
+ *  init_PID: child reaper in ns
+ *  parent_of_init_PID: init_PID's parent, child reaper too
+ *  relative PID level: pid level relative to caller's ns
+ */
+
+#define NS_HIERARCHY	"pidns_hierarchy"
+
+/* list for host pid collection */
+struct pidns_list {
+	struct list_head list;
+	struct pid *pid;
+	unsigned int level;
+};
+
+static void free_pidns_list(struct list_head *head)
+{
+	struct pidns_list *tmp, *pos;
+
+	list_for_each_entry_safe(pos, tmp, head, list) {
+		list_del(&pos->list);
+		put_pid(pos->pid);
+		kfree(pos);
+	}
+}
+
+static int
+pidns_list_add(struct pid *pid, struct list_head *list_head,
+		int level)
+{
+	struct pidns_list *ent;
+
+	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
+	if (!ent)
+		return -ENOMEM;
+
+	ent->pid = pid;
+	ent->level = level;
+	list_add_tail(&ent->list, list_head);
+
+	return 0;
+}
+
+static int
+pidns_list_filter(struct list_head *pidns_pid_list,
+		struct list_head *pidns_pid_tree)
+{
+	struct pidns_list *pos, *pos_t;
+	struct pid_namespace *ns0, *ns1;
+	struct pid *pid0, *pid1;
+	int rc, flag = 0;
+
+	/*
+	 * screen pids with relationship
+	 * in pidns_pid_list, we may add pids like:
+	 * ns0   ns1   ns2
+	 * pid1->pid2->pid3
+	 * we should screen pid1, pid2 and keep pid3
+	 */
+	list_for_each_entry(pos, pidns_pid_list, list) {
+		list_for_each_entry(pos_t, pidns_pid_list, list) {
+			flag = 0;
+			pid0 = pos->pid;
+			pid1 = pos_t->pid;
+			ns0 = pid0->numbers[pid0->level].ns;
+			ns1 = pid1->numbers[pid1->level].ns;
+			if (pos->pid->level < pos_t->pid->level)
+				for (; ns1 != NULL; ns1 = ns1->parent)
+					if (ns0 == ns1) {
+						flag = 1;
+						break;
+					}
+			/* a redundant pid found */
+			if (flag == 1)
+				break;
+		}
+
+		if (flag == 0) {
+			get_pid(pos->pid);
+			rc = pidns_list_add(pos->pid, pidns_pid_tree, 0);
+			if (rc) {
+				put_pid(pos->pid);
+				goto cleanup;
+			}
+		}
+	}
+
+	/*
+	 *  Now all useful stuffs are in pidns_pid_tree,
+	 *  free pidns_pid_list
+	 */
+	free_pidns_list(pidns_pid_list);
+
+	return 0;
+
+cleanup:
+	free_pidns_list(pidns_pid_tree);
+	return rc;
+}
+
+static void
+pidns_list_set_level(struct list_head *pidns_list_in,
+		struct pid_namespace *curr_ns)
+{
+	struct pidns_list *pos, *pos_t;
+	struct pid *pid0, *pid1;
+	int i;
+
+	/*
+	 * From the pid hierarchy point of view,
+	 * we already had a list of pids who are not
+	 * the subsets of each other.
+	 * But part of them may be same.
+	 * We need to set the level of each pids:
+	 * pid0:         A->B->C   pid1:       A->B->D
+	 * level:           2                  0
+	 * We use level to identify
+	 * the public part of each pids.
+	 */
+	list_for_each_entry(pos, pidns_list_in, list) {
+		list_for_each_entry(pos_t, pidns_list_in, list) {
+			pid0 = pos->pid;
+			pid1 = pos_t->pid;
+			if (pid0 == pid1)
+				continue;
+			if (pos_t->level > 0)
+				continue;
+			for (i = curr_ns->level + 1; i <= pid0->level; i++) {
+				/* skip the public parts */
+				if (pid0->numbers[i].ns ==
+						pid1->numbers[i].ns)
+					continue;
+				else
+					break;
+			}
+			pos->level = i - 1;
+		}
+	}
+}
+
+/*
+ * Finds all init pids, places them into
+ * pidns_pid_list and then stores the hierarchy
+ * into pidns_pid_tree.
+ */
+static int proc_pidns_list_refresh(struct pid_namespace *curr_ns,
+		struct list_head *pidns_pid_list,
+		struct list_head *pidns_pid_tree)
+{
+	struct pid *pid;
+	int new_nr, nr = 0;
+	int rc;
+
+	/* collect pids in current namespace */
+	while (nr < PID_MAX_LIMIT) {
+		rcu_read_lock();
+		pid = find_ge_pid(nr, curr_ns);
+		if (!pid) {
+			rcu_read_unlock();
+			break;
+		}
+
+		new_nr = pid_vnr(pid);
+		if (!is_child_reaper(pid)) {
+			nr = new_nr + 1;
+			rcu_read_unlock();
+			continue;
+		}
+		get_pid(pid);
+		rcu_read_unlock();
+		rc = pidns_list_add(pid, pidns_pid_list, 0);
+		if (rc) {
+			put_pid(pid);
+			goto cleanup;
+		}
+		nr = new_nr + 1;
+	}
+
+	/*
+	 * Only one pid found as the child reaper,
+	 * so current pid namespace do not have sub-namespace,
+	 * return 0 directly.
+	 */
+	if (list_is_singular(pidns_pid_list)) {
+		rc = 0;
+		goto cleanup;
+	}
+
+	/*
+	 * screen duplicate pids from pidns_pid_list
+	 * and form a new list pidns_pid_tree.
+	 */
+	rc = pidns_list_filter(pidns_pid_list, pidns_pid_tree);
+	if (rc)
+		goto cleanup;
+
+	return 0;
+
+cleanup:
+	free_pidns_list(pidns_pid_list);
+	return rc;
+}
+
+static int nslist_proc_show(struct seq_file *m, void *v)
+{
+	struct pidns_list *pos;
+	struct pid_namespace *ns, *curr_ns;
+	struct pid *pid;
+	char pid_buf[16], ppid_buf[16];
+	int i, rc;
+
+	LIST_HEAD(pidns_pid_list);
+	LIST_HEAD(pidns_pid_tree);
+
+	curr_ns = task_active_pid_ns(current);
+
+	rc = proc_pidns_list_refresh(curr_ns,
+			&pidns_pid_list, &pidns_pid_tree);
+	if (rc)
+		return rc;
+
+	pidns_list_set_level(&pidns_pid_tree, curr_ns);
+
+	/* print pid namespace's hierarchy */
+	list_for_each_entry(pos, &pidns_pid_tree, list) {
+		pid = pos->pid;
+		for (i = max(curr_ns->level, pos->level) + 1;
+				i <= pid->level; i++) {
+			ns = pid->numbers[i].ns;
+			/* show PID '1' in specific pid ns */
+			snprintf(pid_buf, 16, "%u",
+				pid_vnr(find_pid_ns(1, ns)));
+			ns = pid->numbers[i - 1].ns;
+			snprintf(ppid_buf, 16, "%u",
+					pid_vnr(find_pid_ns(1, ns)));
+			seq_printf(m, "%s\t%s\t%d\n", pid_buf, ppid_buf,
+					i - curr_ns->level);
+		}
+	}
+
+	free_pidns_list(&pidns_pid_tree);
+
+	return 0;
+}
+
+static int nslist_proc_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, nslist_proc_show, NULL);
+}
+
+static const struct file_operations proc_nspid_nslist_fops = {
+	.open		= nslist_proc_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+};
+
+static int __init pidns_hierarchy_init(void)
+{
+	proc_create(NS_HIERARCHY, S_IWUGO,
+		NULL, &proc_nspid_nslist_fops);
+
+	return 0;
+}
+fs_initcall(pidns_hierarchy_init);
-- 
1.9.3

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