[PATCHv5] 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 same 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:

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

It shows the pid hierarchy below:

      init_pid_ns (not showed in /proc/pidns_hierarchy)
              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>
---
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 | 226 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 233 insertions(+)
 create mode 100644 fs/proc/pidns_hierarchy.c

diff --git a/fs/proc/Kconfig b/fs/proc/Kconfig
index 2183fcf..4bb111c 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" if EXPERT
+	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..2f5148c
--- /dev/null
+++ b/fs/proc/pidns_hierarchy.c
@@ -0,0 +1,226 @@
+#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>
+
+/*
+ *  /proc/pidns_hierarchy
+ *
+ *  show the hierarchy of pid namespace
+ */
+
+#define NS_HIERARCHY	"pidns_hierarchy"
+
+/* list for host pid collection */
+struct pidns_list {
+	struct list_head list;
+	struct pid *pid;
+};
+
+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,
+		struct pid_namespace *curr_ns)
+{
+	struct pidns_list *ent;
+	struct pid_namespace *ns;
+
+	ent = kmalloc(sizeof(*ent), GFP_KERNEL);
+	if (!ent)
+		return -ENOMEM;
+
+	ent->pid = pid;
+	ns = pid->numbers[pid->level].ns;
+	if (curr_ns) {
+		/* add pids who is the child of curr_ns */
+		for (; ns != NULL; ns = ns->parent)
+			if (ns == curr_ns) {
+				list_add_tail(&ent->list, list_head);
+				break;
+			}
+	} else
+		list_add_tail(&ent->list, list_head);
+
+	return 0;
+}
+
+static int
+pidns_list_filter(struct list_head *pidns_list,
+		struct list_head *pidns_tree)
+{
+	struct pidns_list *pos, *pos_t;
+	struct pid_namespace *ns0, *ns1;
+	struct pid *pid0, *pid1;
+	int rc, flag = 0;
+
+	/* screen pid with relationship
+	 * in pidns_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_list, list) {
+		list_for_each_entry(pos_t, pidns_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;
+					}
+			if (flag == 1)
+				break;
+		}
+
+		if (flag == 0) {
+			rcu_read_lock();
+			get_pid(pos->pid);
+			rcu_read_unlock();
+			rc = pidns_list_add(pos->pid, pidns_tree, NULL);
+			if (rc)
+				goto out;
+		}
+	}
+
+	/* Now all usefull stuffs are in pidns_tree, free pidns_list*/
+	free_pidns_list(pidns_list);
+
+	return 0;
+
+out:
+	free_pidns_list(pidns_tree);
+	return rc;
+}
+
+/* collect pids in pidns_list,
+ * then remove duplicated ones,
+ * add the rest to pidns_tree
+ */
+static int proc_pidns_list_refresh(struct pid_namespace *curr_ns,
+		struct list_head *pidns_list,
+		struct list_head *pidns_tree)
+{
+	struct pid *pid;
+	int new_nr, nr = 0;
+	int rc;
+
+	/* collect pid in differet ns */
+	while (nr < PID_MAX_LIMIT) {
+		rcu_read_lock();
+		pid = find_ge_pid(nr, curr_ns);
+		if (pid) {
+			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_list, curr_ns);
+			if (rc)
+				goto out;
+		} else {
+			rcu_read_unlock();
+			break;
+		}
+		nr = new_nr + 1;
+	}
+
+	/* Only one pid found as child reaper,
+	 * no sub-namespace of current pid namespace,
+	 * return 0 directly.
+	 */
+	if (list_is_singular(pidns_list)) {
+		rc = 0;
+		goto out;
+	}
+
+	/* screen duplicate pids from list pidns_list
+	* and form a new list pidns_tree
+	*/
+	rc = pidns_list_filter(pidns_list, pidns_tree);
+	if (rc)
+		goto out;
+
+	return 0;
+
+out:
+	free_pidns_list(pidns_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];
+	int i, rc;
+
+	LIST_HEAD(pidns_list);
+	LIST_HEAD(pidns_tree);
+
+	curr_ns = task_active_pid_ns(current);
+
+	rc = proc_pidns_list_refresh(curr_ns, &pidns_list, &pidns_tree);
+	if (rc)
+		return rc;
+
+	/* print pid namespace hierarchy */
+	list_for_each_entry(pos, &pidns_tree, list) {
+		pid = pos->pid;
+		for (i = curr_ns->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)));
+			seq_printf(m, "%s ", pid_buf);
+		}
+
+		seq_putc(m, '\n');
+	}
+
+	free_pidns_list(&pidns_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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