[iproute2-next,v2,1/3] ss: introduce cgroup2 cache and helper functions

diff --git a/include/cg_map.h b/include/cg_map.h
new file mode 100644
index 0000000..d30517f
--- /dev/null
+++ b/include/cg_map.h
@@ -0,0 +1,6 @@ 
+#ifndef __CG_MAP_H__
+#define __CG_MAP_H__
+
+const char *cg_id_to_path(__u64 id);
+
+#endif /* __CG_MAP_H__ */
diff --git a/include/utils.h b/include/utils.h
index 001491a..7041c46 100644
--- a/include/utils.h
+++ b/include/utils.h
@@ -302,7 +302,9 @@  int get_real_family(int rtm_type, int rtm_family);
 int cmd_exec(const char *cmd, char **argv, bool do_fork,
 	     int (*setup)(void *), void *arg);
 int make_path(const char *path, mode_t mode);
-char *find_cgroup2_mount(void);
+char *find_cgroup2_mount(bool do_mount);
+__u64 get_cgroup2_id(const char *path);
+char *get_cgroup2_path(__u64 id, bool full);
 int get_command_name(const char *pid, char *comm, size_t len);
 
 int get_rtnl_link_stats_rta(struct rtnl_link_stats64 *stats64,
diff --git a/ip/ipvrf.c b/ip/ipvrf.c
index b9a4367..28dd8e2 100644
--- a/ip/ipvrf.c
+++ b/ip/ipvrf.c
@@ -225,7 +225,7 @@  static int ipvrf_pids(int argc, char **argv)
 		return -1;
 	}
 
-	mnt = find_cgroup2_mount();
+	mnt = find_cgroup2_mount(true);
 	if (!mnt)
 		return -1;
 
@@ -366,7 +366,7 @@  static int vrf_switch(const char *name)
 		}
 	}
 
-	mnt = find_cgroup2_mount();
+	mnt = find_cgroup2_mount(true);
 	if (!mnt)
 		return -1;
 
diff --git a/lib/Makefile b/lib/Makefile
index bab8cbf..7cba185 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -5,7 +5,7 @@  CFLAGS += -fPIC
 
 UTILOBJ = utils.o rt_names.o ll_map.o ll_types.o ll_proto.o ll_addr.o \
 	inet_proto.o namespace.o json_writer.o json_print.o \
-	names.o color.o bpf.o exec.o fs.o
+	names.o color.o bpf.o exec.o fs.o cg_map.o
 
 NLOBJ=libgenl.o libnetlink.o
 
diff --git a/lib/cg_map.c b/lib/cg_map.c
new file mode 100644
index 0000000..77f030e
--- /dev/null
+++ b/lib/cg_map.c
@@ -0,0 +1,135 @@ 
+/*
+ * cg_map.c	cgroup v2 cache
+ *
+ *		This program is free software; you can redistribute it and/or
+ *		modify it under the terms of the GNU General Public License
+ *		as published by the Free Software Foundation; either version
+ *		2 of the License, or (at your option) any later version.
+ *
+ * Authors:	Dmitry Yakunin <zeil@yandex-team.ru>
+ */
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <linux/types.h>
+#include <linux/limits.h>
+#include <ftw.h>
+
+#include "cg_map.h"
+#include "list.h"
+#include "utils.h"
+
+struct cg_cache {
+	struct hlist_node id_hash;
+	__u64	id;
+	char	path[];
+};
+
+#define IDMAP_SIZE	1024
+static struct hlist_head id_head[IDMAP_SIZE];
+
+static struct cg_cache *cg_get_by_id(__u64 id)
+{
+	unsigned int h = id & (IDMAP_SIZE - 1);
+	struct hlist_node *n;
+
+	hlist_for_each(n, &id_head[h]) {
+		struct cg_cache *cg;
+
+		cg = container_of(n, struct cg_cache, id_hash);
+		if (cg->id == id)
+			return cg;
+	}
+
+	return NULL;
+}
+
+static struct cg_cache *cg_entry_create(__u64 id, const char *path)
+{
+	unsigned int h = id & (IDMAP_SIZE - 1);
+	struct cg_cache *cg;
+
+	cg = malloc(sizeof(*cg) + strlen(path) + 1);
+	if (!cg) {
+		fprintf(stderr,
+			"Failed to allocate memory for cgroup2 cache entry");
+		return NULL;
+	}
+	cg->id = id;
+	strcpy(cg->path, path);
+
+	hlist_add_head(&cg->id_hash, &id_head[h]);
+
+	return cg;
+}
+
+static int mntlen;
+
+static int nftw_fn(const char *fpath, const struct stat *sb,
+		   int typeflag, struct FTW *ftw)
+{
+	const char *path;
+	__u64 id;
+
+	if (typeflag != FTW_D)
+		return 0;
+
+	id = get_cgroup2_id(fpath);
+	if (!id)
+		return -1;
+
+	path = fpath + mntlen;
+	if (*path == '\0')
+		/* root cgroup */
+		path = "/";
+	if (!cg_entry_create(id, path))
+		return -1;
+
+	return 0;
+}
+
+static void cg_init_map(void)
+{
+	char *mnt;
+
+	mnt = find_cgroup2_mount(false);
+	if (!mnt)
+		exit(1);
+
+	mntlen = strlen(mnt);
+	if (nftw(mnt, nftw_fn, 1024, FTW_MOUNT) < 0)
+		exit(1);
+
+	free(mnt);
+}
+
+const char *cg_id_to_path(__u64 id)
+{
+	static int initialized;
+	static char buf[64];
+
+	const struct cg_cache *cg;
+	char *path;
+
+	if (!initialized) {
+		cg_init_map();
+		initialized = 1;
+	}
+
+	cg = cg_get_by_id(id);
+	if (cg)
+		return cg->path;
+
+	path = get_cgroup2_path(id, false);
+	if (path) {
+		cg = cg_entry_create(id, path);
+		free(path);
+		if (cg)
+			return cg->path;
+	}
+
+	snprintf(buf, sizeof(buf), "unreachable:%llx", id);
+	return buf;
+}
diff --git a/lib/fs.c b/lib/fs.c
index 86efd4e..e265fc0 100644
--- a/lib/fs.c
+++ b/lib/fs.c
@@ -59,13 +59,18 @@  static char *find_fs_mount(const char *fs_to_find)
 }
 
 /* caller needs to free string returned */
-char *find_cgroup2_mount(void)
+char *find_cgroup2_mount(bool do_mount)
 {
 	char *mnt = find_fs_mount(CGROUP2_FS_NAME);
 
 	if (mnt)
 		return mnt;
 
+	if (!do_mount) {
+		fprintf(stderr, "Failed to find cgroup2 mount\n");
+		return NULL;
+	}
+
 	mnt = strdup(MNT_CGRP2_PATH);
 	if (!mnt) {
 		fprintf(stderr, "Failed to allocate memory for cgroup2 path\n");
@@ -74,7 +79,7 @@  char *find_cgroup2_mount(void)
 	}
 
 	if (make_path(mnt, 0755)) {
-		fprintf(stderr, "Failed to setup vrf cgroup2 directory\n");
+		fprintf(stderr, "Failed to setup cgroup2 directory\n");
 		free(mnt);
 		return NULL;
 	}
@@ -99,6 +104,134 @@  out:
 	return mnt;
 }
 
+__u64 get_cgroup2_id(const char *path)
+{
+	char fh_buf[sizeof(struct file_handle) + sizeof(__u64)] = { 0 };
+	struct file_handle *fhp = (struct file_handle *)fh_buf;
+	union {
+		__u64 id;
+		unsigned char bytes[sizeof(__u64)];
+	} cg_id = { .id = 0 };
+	char *mnt = NULL;
+	int mnt_fd = -1;
+	int mnt_id;
+
+	if (!path) {
+		fprintf(stderr, "Invalid cgroup2 path\n");
+		return 0;
+	}
+
+	fhp->handle_bytes = sizeof(__u64);
+	if (name_to_handle_at(AT_FDCWD, path, fhp, &mnt_id, 0) < 0) {
+		/* try at cgroup2 mount */
+
+		while (*path == '/')
+			path++;
+		if (*path == '\0') {
+			fprintf(stderr, "Invalid cgroup2 path\n");
+			goto out;
+		}
+
+		mnt = find_cgroup2_mount(false);
+		if (!mnt)
+			goto out;
+
+		mnt_fd = open(mnt, O_RDONLY);
+		if (mnt_fd < 0) {
+			fprintf(stderr, "Failed to open cgroup2 mount\n");
+			goto out;
+		}
+
+		fhp->handle_bytes = sizeof(__u64);
+		if (name_to_handle_at(mnt_fd, path, fhp, &mnt_id, 0) < 0) {
+			fprintf(stderr, "Failed to get cgroup2 ID: %s\n",
+					strerror(errno));
+			goto out;
+		}
+		if (fhp->handle_bytes != sizeof(__u64)) {
+			fprintf(stderr, "Invalid size of cgroup2 ID\n");
+			goto out;
+		}
+	}
+
+	memcpy(cg_id.bytes, fhp->f_handle, sizeof(__u64));
+
+out:
+	close(mnt_fd);
+	free(mnt);
+
+	return cg_id.id;
+}
+
+#define FILEID_INO32_GEN 1
+
+/* caller needs to free string returned */
+char *get_cgroup2_path(__u64 id, bool full)
+{
+	char fh_buf[sizeof(struct file_handle) + sizeof(__u64)] = { 0 };
+	struct file_handle *fhp = (struct file_handle *)fh_buf;
+	union {
+		__u64 id;
+		unsigned char bytes[sizeof(__u64)];
+	} cg_id = { .id = id };
+	int mnt_fd = -1, fd = -1;
+	char link_buf[PATH_MAX];
+	char *path = NULL;
+	char fd_path[64];
+	int link_len;
+	char *mnt;
+
+	if (!id) {
+		fprintf(stderr, "Invalid cgroup2 ID\n");
+		return NULL;
+	}
+
+	mnt = find_cgroup2_mount(false);
+	if (!mnt)
+		return NULL;
+
+	mnt_fd = open(mnt, O_RDONLY);
+	if (mnt_fd < 0) {
+		fprintf(stderr, "Failed to open cgroup2 mount\n");
+		goto out;
+	}
+
+	fhp->handle_bytes = sizeof(__u64);
+	fhp->handle_type = FILEID_INO32_GEN;
+	memcpy(fhp->f_handle, cg_id.bytes, sizeof(__u64));
+
+	fd = open_by_handle_at(mnt_fd, fhp, 0);
+	if (fd < 0) {
+		fprintf(stderr, "Failed to open cgroup2 by ID\n");
+		goto out;
+	}
+
+	snprintf(fd_path, sizeof(fd_path), "/proc/self/fd/%d", fd);
+	link_len = readlink(fd_path, link_buf, sizeof(link_buf) - 1);
+	if (link_len < 0) {
+		fprintf(stderr,
+			"Failed to read value of symbolic link %s\n",
+			fd_path);
+		goto out;
+	}
+	link_buf[link_len] = '\0';
+
+	if (full)
+		path = strdup(link_buf);
+	else
+		path = strdup(link_buf + strlen(mnt));
+	if (!path)
+		fprintf(stderr,
+			"Failed to allocate memory for cgroup2 path\n");
+
+out:
+	close(fd);
+	close(mnt_fd);
+	free(mnt);
+
+	return path;
+}
+
 int make_path(const char *path, mode_t mode)
 {
 	char *dir, *delim;