[RFC,iproute,v1,3/4] afnetns: introduce lib/afnetns.c and a name cache

diff --git a/include/afnetns.h b/include/afnetns.h
new file mode 100644
index 00000000000000..287bcb6153611b
--- /dev/null
+++ b/include/afnetns.h
@@ -0,0 +1,6 @@ 
+#pragma once
+
+#define AFNETNS_RUN_DIR "/var/run/afnetns"
+
+int afnetns_open(const char *name);
+char *afnetns_lookup_name(ino_t inode);
diff --git a/include/namespace.h b/include/namespace.h
index e0745ab0b50972..8193e474a75f98 100644
--- a/include/namespace.h
+++ b/include/namespace.h
@@ -7,7 +7,6 @@ 
 #include <sys/syscall.h>
 #include <errno.h>
 
-#define AFNETNS_RUN_DIR "/var/run/afnetns"
 #define NETNS_RUN_DIR "/var/run/netns"
 #define NETNS_ETC_DIR "/etc/netns"
 
@@ -52,8 +51,6 @@  int netns_switch(char *netns);
 int netns_get_fd(const char *netns);
 int netns_foreach(int (*func)(char *nsname, void *arg), void *arg);
 
-int afnetns_open(const char *name);
-
 struct netns_func {
 	int (*func)(char *nsname, void *arg);
 	void *arg;
diff --git a/ip/ipaddress.c b/ip/ipaddress.c
index 2994b6a3e0a154..d954f3ea5bff40 100644
--- a/ip/ipaddress.c
+++ b/ip/ipaddress.c
@@ -38,6 +38,7 @@ 
 #include "xdp.h"
 #include "color.h"
 #include "namespace.h"
+#include "afnetns.h"
 
 enum {
 	IPADD_LIST,
@@ -1004,7 +1005,7 @@  static int afnetns_get_fd(const char *name)
 {
 	int ns = -1;
 
-	if (name[0] == '/')
+	if (strnlen(name, 1) && name[0] == '/')
 		ns = open(name, O_RDONLY | O_CLOEXEC);
 	else
 		ns = afnetns_open(name);
@@ -1219,8 +1220,13 @@  int print_addrinfo(const struct sockaddr_nl *who, struct nlmsghdr *n,
 		}
 	}
 	if (rta_tb[IFA_AFNETNS_INODE]) {
-		fprintf(fp, " afnet:[%u]",
-			rta_getattr_u32(rta_tb[IFA_AFNETNS_INODE]));
+		ino_t inode;
+		char *name;
+
+		inode = rta_getattr_u32(rta_tb[IFA_AFNETNS_INODE]);
+		name = afnetns_lookup_name(inode);
+		if (name)
+			fprintf(fp, " afnet %s", name);
 	}
 	fprintf(fp, "\n");
 brief_exit:
diff --git a/ip/ipafnetns.c b/ip/ipafnetns.c
index 5a197ad3866d18..2fd749a3f20628 100644
--- a/ip/ipafnetns.c
+++ b/ip/ipafnetns.c
@@ -7,6 +7,7 @@ 
 #include "utils.h"
 #include "ip_common.h"
 #include "namespace.h"
+#include "afnetns.h"
 
 static void usage(void)
 {
diff --git a/lib/Makefile b/lib/Makefile
index 1d24ca24b9a39f..7825021ea3cfa8 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -8,7 +8,7 @@  CFLAGS += -fPIC
 
 UTILOBJ = utils.o rt_names.o ll_types.o ll_proto.o ll_addr.o \
 	inet_proto.o namespace.o json_writer.o \
-	names.o color.o bpf.o exec.o fs.o
+	names.o color.o bpf.o exec.o fs.o afnetns.o
 
 NLOBJ=libgenl.o ll_map.o libnetlink.o
 
diff --git a/lib/afnetns.c b/lib/afnetns.c
new file mode 100644
index 00000000000000..d58a55df46daa7
--- /dev/null
+++ b/lib/afnetns.c
@@ -0,0 +1,226 @@ 
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdbool.h>
+#include <string.h>
+#include <errno.h>
+#include <limits.h>
+
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include <dirent.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+#include <math.h>
+
+#include "list.h"
+#include "afnetns.h"
+
+#define ULONG_CHARS ((int)ceill(log10l(ULONG_MAX)))
+
+static struct inode_cache {
+	struct inode_cache *next;
+	ino_t inode;
+	char name[];
+} *cache[64];
+
+static int self_inode(ino_t *me)
+{
+	static bool initialized;
+	static ino_t inode;
+	long path_size;
+	char *path;
+	int err;
+
+	if (initialized) {
+		*me = inode;
+		return 0;
+	}
+
+	errno = 0;
+	path_size = pathconf("/proc/self/ns/afnet", _PC_PATH_MAX);
+	if (path_size < 0) {
+		if (errno)
+			perror("pathconf");
+		else
+			fprintf(stderr,
+				"couldn't determine _PC_PATH_MAX for procfs: %zd\n",
+				path_size);
+		return -1;
+	}
+
+	path = malloc(path_size);
+	if (!path) {
+		perror("malloc");
+		return -1;
+	}
+
+	err = readlink("/proc/self/ns/afnet", path, path_size);
+	if (err < 0) {
+		perror("readlink");
+		goto out;
+	} else if (err >= path_size) {
+		fprintf(stderr, "readlink(\"/proc/self/ns/afnet\") exceeded maximum path length: %d >= %ld",
+			err, path_size);
+		err = -1;
+		goto out;
+	}
+	path[err] = '\0';
+
+	if (sscanf(path, "afnet:[%lu]", &inode) != 1) {
+		perror("sscanf");
+		err = -1;
+		goto out;
+	}
+
+	initialized = true;
+	*me = inode;
+	err = 0;
+out:
+	free(path);
+	return err;
+}
+
+static struct inode_cache **lookup_node(ino_t inode)
+{
+	struct inode_cache **node;
+
+	node = cache + (inode & 63);
+	while (*node && node[0]->inode != inode)
+		node = &node[0]->next;
+
+	return node;
+}
+
+static void fill_cache(void)
+{
+	struct dirent *ent;
+	ino_t me;
+	DIR *dir;
+
+	if (self_inode(&me))
+		return;
+
+	dir = opendir(AFNETNS_RUN_DIR);
+	if (!dir)
+		return;
+
+	errno = 0;
+	while ((ent = readdir(dir))) {
+		struct inode_cache **node;
+		struct stat buf;
+		ino_t inode;
+		bool self;
+		char *end;
+		int fd;
+
+		if (!strcmp(ent->d_name, ".") ||
+		    !strcmp(ent->d_name, ".."))
+			continue;
+
+		fd = dirfd(dir);
+		if (fd < 0) {
+			perror("dirfd");
+			continue;
+		}
+
+		if (fstatat(fd, ent->d_name, &buf, 0)) {
+			perror("fstatat");
+			continue;
+		}
+
+		inode = buf.st_ino;
+		self = me == inode;
+
+		node = lookup_node(inode);
+		if (*node)
+			continue;
+
+		*node = malloc(sizeof(**node)
+			       + strlen(ent->d_name)
+			       + (self ? strlen(",self") : 0)
+			       + 1);
+		if (!*node)
+			continue;
+
+		node[0]->next = NULL;
+		node[0]->inode = inode;
+		end  = stpcpy(node[0]->name, ent->d_name);
+		if (self)
+			strcpy(end, ",self");
+
+		errno = 0;
+	}
+
+	if (errno)
+		perror("readdir");
+
+	if (closedir(dir))
+		perror("closedir");
+}
+
+static char *lookup_cache(ino_t inode)
+{
+	struct inode_cache **node;
+	bool self;
+	ino_t me;
+
+	node = lookup_node(inode);
+	if (*node)
+		return node[0]->name;
+
+	if (self_inode(&me))
+		return NULL;
+
+	self = me == inode;
+
+	*node = malloc(sizeof(**node) + ULONG_CHARS + strlen("afnet:[]") + 1 +
+		       (self ? strlen(",self") : 0));
+	if (!*node)
+		return NULL;
+
+	if (sprintf(node[0]->name, "afnet:[%lu]%s", inode, self ? ",self" : "") < 0) {
+		free(*node);
+		*node = NULL;
+		return NULL;
+	}
+
+	node[0]->next = NULL;
+	node[0]->inode = inode;
+	return node[0]->name;
+}
+
+char *afnetns_lookup_name(ino_t inode)
+{
+	static bool initialized = false;
+
+	if (!initialized) {
+		fill_cache();
+		initialized = true;
+	}
+
+	return lookup_cache(inode);
+}
+
+int afnetns_open(const char *name)
+{
+	int ns;
+	char *path;
+
+	ns = asprintf(&path, "%s/%s", AFNETNS_RUN_DIR, name);
+	if (ns < 0) {
+		perror("asprintf");
+		return ns;
+	};
+
+	ns = open(path, O_RDONLY | O_CLOEXEC);
+	if (ns < 0) {
+		fprintf(stderr, "Cannot open afnet namespace \"%s\": %s\n",
+			name, strerror(errno));
+	}
+
+	free(path);
+	return ns;
+}
+
diff --git a/lib/namespace.c b/lib/namespace.c
index f20e5b6ef5a3ef..30b513889e6e24 100644
--- a/lib/namespace.c
+++ b/lib/namespace.c
@@ -124,24 +124,3 @@  int netns_foreach(int (*func)(char *nsname, void *arg), void *arg)
 	closedir(dir);
 	return 0;
 }
-
-int afnetns_open(const char *name)
-{
-	int ns;
-	char *path;
-
-	ns = asprintf(&path, "%s/%s", AFNETNS_RUN_DIR, name);
-	if (ns < 0) {
-		perror("asprintf");
-		return ns;
-	};
-
-	ns = open(path, O_RDONLY | O_CLOEXEC);
-	if (ns < 0) {
-		fprintf(stderr, "Cannot open afnet namespace \"%s\": %s\n",
-			name, strerror(errno));
-	}
-
-	free(path);
-	return ns;
-}