Add option parsing to nsenter and enable specifying commands with arg…

…uments.

Docker-DCO-1.1-Signed-off-by: Mrunal Patel <mrunalp@gmail.com> (github: mrunalp)

namespaces/execin.go

@@ -21,14 +21,8 @@ func ExecIn(container *libcontainer.Container, nspid int, args []string) error {
 		return err
 	}
 
-	// TODO(vmarmol): Move this to the container JSON.
-	processLabel, err := label.GetPidCon(nspid)
-	if err != nil {
-		return err
-	}
-
 	// Enter the namespace and then finish setup
-	finalArgs := []string{os.Args[0], "nsenter", strconv.Itoa(nspid), processLabel, string(containerJson)}
+	finalArgs := []string{os.Args[0], "nsenter", "--nspid", strconv.Itoa(nspid), "--containerjson", string(containerJson), "--"}
 	finalArgs = append(finalArgs, args...)
 	if err := system.Execv(finalArgs[0], finalArgs[0:], os.Environ()); err != nil {
 		return err
@@ -37,7 +31,7 @@ func ExecIn(container *libcontainer.Container, nspid int, args []string) error {
 }
 
 // NsEnter is run after entering the namespace.
-func NsEnter(container *libcontainer.Container, processLabel string, nspid int, args []string) error {
+func NsEnter(container *libcontainer.Container, nspid int, args []string) error {
 	// clear the current processes env and replace it with the environment
 	// defined on the container
 	if err := LoadContainerEnvironment(container); err != nil {
@@ -46,9 +40,13 @@ func NsEnter(container *libcontainer.Container, processLabel string, nspid int,
 	if err := FinalizeNamespace(container); err != nil {
 		return err
 	}
-	if err := label.SetProcessLabel(processLabel); err != nil {
-		return err
+
+	if process_label, ok := container.Context["process_label"]; ok {
+		if err := label.SetProcessLabel(process_label); err != nil {
+			return err
+		}
 	}
+
 	if err := system.Execv(args[0], args[0:], container.Env); err != nil {
 		return err
 	}

namespaces/nsenter.go

@@ -15,6 +15,7 @@ package namespaces
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
+#include <getopt.h>
 
 static const kBufSize = 256;
 
@@ -64,6 +65,10 @@ int setns(int fd, int nstype) {
 #endif
 #endif
 
+void print_usage() {
+	fprintf(stderr, "<binary> nsenter --nspid <pid> --containerjson <container_json> -- cmd1 arg1 arg2...\n");
+}
+
 void nsenter() {
 	int argc;
 	char **argv;
@@ -79,11 +84,40 @@ void nsenter() {
 		fprintf(stderr, "nsenter: Incorrect usage, not enough arguments\n");
 		exit(1);
 	}
-	pid_t init_pid = strtol(argv[2], NULL, 10);
+
+	static const struct option longopts[] = {
+		{ "nspid",         required_argument, NULL, 'n' },
+		{ "containerjson", required_argument, NULL, 'c' },
+		{ NULL,            0,                 NULL,  0  }
+	};
+
+	int c;
+	pid_t init_pid = -1;
+	char *init_pid_str = NULL;
+	char *container_json = NULL;
+	while ((c = getopt_long_only(argc, argv, "n:s:c:", longopts, NULL)) != -1) {
+		switch (c) {
+		case 'n':
+			init_pid_str = optarg;
+			break;
+		case 'c':
+			container_json = optarg;
+			break;
+		}
+	}
+
+	if (container_json == NULL || init_pid_str == NULL) {
+		print_usage();
+		exit(1);
+	}
+
+	init_pid = strtol(init_pid_str, NULL, 10);
 	if (errno != 0 || init_pid <= 0) {
-		fprintf(stderr, "nsenter: Failed to parse PID from \"%s\" with error: \"%s\"\n", argv[2], strerror(errno));
+		fprintf(stderr, "nsenter: Failed to parse PID from \"%s\" with error: \"%s\"\n", init_pid_str, strerror(errno));
+		print_usage();
 		exit(1);
 	}
+
 	argc -= 3;
 	argv += 3;
 

nsinit/nsenter.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"log"
-	"strconv"
 
 	"github.com/codegangsta/cli"
 	"github.com/docker/libcontainer/namespaces"
@@ -12,29 +11,30 @@ var nsenterCommand = cli.Command{
 	Name:   "nsenter",
 	Usage:  "init process for entering an existing namespace",
 	Action: nsenterAction,
+	Flags: []cli.Flag{
+		cli.IntFlag{Name: "nspid"},
+		cli.StringFlag{Name: "containerjson"},
+	},
 }
 
 func nsenterAction(context *cli.Context) {
 	args := context.Args()
-	if len(args) < 4 {
-		log.Fatalf("incorrect usage: <pid> <process label> <container JSON> <cmd>...")
-	}
 
-	container, err := loadContainerFromJson(args.Get(2))
-	if err != nil {
-		log.Fatalf("unable to load container: %s", err)
+	if len(args) == 0 {
+		args = []string{"/bin/bash"}
 	}
 
-	nspid, err := strconv.Atoi(args.Get(0))
+	container, err := loadContainerFromJson(context.String("containerjson"))
 	if err != nil {
-		log.Fatalf("unable to read pid: %s from %q", err, args.Get(0))
+		log.Fatalf("unable to load container: %s", err)
 	}
 
+	nspid := context.Int("nspid")
 	if nspid <= 0 {
 		log.Fatalf("cannot enter into namespaces without valid pid: %q", nspid)
 	}
 
-	if err := namespaces.NsEnter(container, args.Get(1), nspid, args[3:]); err != nil {
+	if err := namespaces.NsEnter(container, nspid, args); err != nil {
 		log.Fatalf("failed to nsenter: %s", err)
 	}
 }