lxc: add clone hook.

Add a clone hook called from api_clone.  Pass arguments to it from
lxc_clone.c.

The clone update hook is called while the container's bdev is mounted.
Information about the container is passed in through environment
variables LXC_ROOTFS_PATH, LXC_NAME, The LXC_ROOTFS_MOUNT, and
LXC_CONFIG_FILE.

LXC_ROOTFS_MOUNT=/usr/lib/x86_64-linux-gnu/lxc
LXC_CONFIG_FILE=/var/lib/lxc/demo3/config
LXC_ROOTFS_PATH=/var/lib/lxc/demo3/rootfs
LXC_NAME=demo3

So from the hook, updates to the container should be made under
$LXC_ROOTFS_MOUNT/ .

The hook also receives command line arguments as follows:
First argument is container name, second is always 'lxc', third
is the hook name (always clone), then come the arguments which
were passed to lxc-clone.  I.e. when I did:

sudo lxc-clone demo2 demo3 -- hey there dude

the arguments passed in were "demo3 lxc clone hey there dude"

I personally would like to drop the first two arguments.  The
name is available as $LXC_NAME, and the section argument ('lxc')
is meaningless.  However, doing so risks invalidating existing
hooks.

Soon analogous create and destroy hooks will be added as well.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>

src/lxc/conf.c

@@ -173,7 +173,7 @@ return -1;
 #endif
 
 char *lxchook_names[NUM_LXC_HOOKS] = {
-	"pre-start", "pre-mount", "mount", "autodev", "start", "post-stop" };
+	"pre-start", "pre-mount", "mount", "autodev", "start", "post-stop", "clone" };
 
 typedef int (*instanciate_cb)(struct lxc_handler *, struct lxc_netdev *);
 
@@ -336,6 +336,55 @@ static int run_buffer(char *buffer)
 	return 0;
 }
 
+static int run_script_argv(const char *name, const char *section,
+		      const char *script, const char *hook, char **argsin)
+{
+	int ret, i;
+	char *buffer;
+	size_t size = 0;
+
+	INFO("Executing script '%s' for container '%s', config section '%s'",
+	     script, name, section);
+
+	for (i=0; argsin && argsin[i]; i++)
+		size += strlen(argsin[i]) + 1;
+
+	size += strlen(hook) + 1;
+
+	size += strlen(script);
+	size += strlen(name);
+	size += strlen(section);
+	size += 3;
+
+	if (size > INT_MAX)
+		return -1;
+
+	buffer = alloca(size);
+	if (!buffer) {
+		ERROR("failed to allocate memory");
+		return -1;
+	}
+
+	ret = snprintf(buffer, size, "%s %s %s %s", script, name, section, hook);
+	if (ret < 0 || ret >= size) {
+		ERROR("Script name too long");
+		return -1;
+	}
+
+	for (i=0; argsin && argsin[i]; i++) {
+		int len = size-ret;
+		int rc;
+		rc = snprintf(buffer + ret, len, " %s", argsin[i]);
+		if (rc < 0 || rc >= len) {
+			ERROR("Script args too long");
+			return -1;
+		}
+		ret += rc;
+	}
+
+	return run_buffer(buffer);
+}
+
 static int run_script(const char *name, const char *section,
 		      const char *script, ...)
 {
@@ -2765,7 +2814,7 @@ int lxc_setup(const char *name, struct lxc_conf *lxc_conf)
 		return -1;
 	}
 
-	if (run_lxc_hooks(name, "pre-mount", lxc_conf)) {
+	if (run_lxc_hooks(name, "pre-mount", lxc_conf, NULL)) {
 		ERROR("failed to run pre-mount hooks for container '%s'.", name);
 		return -1;
 	}
@@ -2792,13 +2841,13 @@ int lxc_setup(const char *name, struct lxc_conf *lxc_conf)
 		return -1;
 	}
 
-	if (run_lxc_hooks(name, "mount", lxc_conf)) {
+	if (run_lxc_hooks(name, "mount", lxc_conf, NULL)) {
 		ERROR("failed to run mount hooks for container '%s'.", name);
 		return -1;
 	}
 
 	if (lxc_conf->autodev) {
-		if (run_lxc_hooks(name, "autodev", lxc_conf)) {
+		if (run_lxc_hooks(name, "autodev", lxc_conf, NULL)) {
 			ERROR("failed to run autodev hooks for container '%s'.", name);
 			return -1;
 		}
@@ -2865,7 +2914,7 @@ int lxc_setup(const char *name, struct lxc_conf *lxc_conf)
 	return 0;
 }
 
-int run_lxc_hooks(const char *name, char *hook, struct lxc_conf *conf)
+int run_lxc_hooks(const char *name, char *hook, struct lxc_conf *conf, char *argv[])
 {
 	int which = -1;
 	struct lxc_list *it;
@@ -2882,12 +2931,14 @@ int run_lxc_hooks(const char *name, char *hook, struct lxc_conf *conf)
 		which = LXCHOOK_START;
 	else if (strcmp(hook, "post-stop") == 0)
 		which = LXCHOOK_POSTSTOP;
+	else if (strcmp(hook, "clone") == 0)
+		which = LXCHOOK_CLONE;
 	else
 		return -1;
 	lxc_list_for_each(it, &conf->hooks[which]) {
 		int ret;
 		char *hookname = it->elem;
-		ret = run_script(name, "lxc", hookname, hook, NULL);
+		ret = run_script_argv(name, "lxc", hookname, hook, argv);
 		if (ret)
 			return ret;
 	}

src/lxc/conf.h

@@ -237,7 +237,7 @@ struct lxc_rootfs {
  */
 enum lxchooks {
 	LXCHOOK_PRESTART, LXCHOOK_PREMOUNT, LXCHOOK_MOUNT, LXCHOOK_AUTODEV,
-	LXCHOOK_START, LXCHOOK_POSTSTOP, NUM_LXC_HOOKS};
+	LXCHOOK_START, LXCHOOK_POSTSTOP, LXCHOOK_CLONE, NUM_LXC_HOOKS};
 extern char *lxchook_names[NUM_LXC_HOOKS];
 
 struct saved_nic {
@@ -284,7 +284,7 @@ struct lxc_conf {
 	char *rcfile;	// Copy of the top level rcfile we read
 };
 
-int run_lxc_hooks(const char *name, char *hook, struct lxc_conf *conf);
+int run_lxc_hooks(const char *name, char *hook, struct lxc_conf *conf, char *argv[]);
 
 extern int setup_cgroup(const char *cgpath, struct lxc_list *cgroups);
 extern int setup_cgroup_devices(const char *cgpath, struct lxc_list *cgroups);

src/lxc/confile.c

@@ -117,6 +117,7 @@ static struct lxc_config_t config[] = {
 	{ "lxc.hook.autodev",         config_hook                 },
 	{ "lxc.hook.start",           config_hook                 },
 	{ "lxc.hook.post-stop",       config_hook                 },
+	{ "lxc.hook.clone",           config_hook                 },
 	{ "lxc.network.type",         config_network_type         },
 	{ "lxc.network.flags",        config_network_flags        },
 	{ "lxc.network.link",         config_network_link         },
@@ -894,6 +895,8 @@ static int config_hook(const char *key, const char *value,
 		return add_hook(lxc_conf, LXCHOOK_START, copy);
 	else if (strcmp(key, "lxc.hook.post-stop") == 0)
 		return add_hook(lxc_conf, LXCHOOK_POSTSTOP, copy);
+	else if (strcmp(key, "lxc.hook.clone") == 0)
+		return add_hook(lxc_conf, LXCHOOK_CLONE, copy);
 	SYSERROR("Unknown key: %s", key);
 	free(copy);
 	return -1;

src/lxc/lxc_clone.c

@@ -16,7 +16,7 @@
 
 lxc_log_define(lxc_clone, lxc);
 
-void usage(char *me)
+void usage(const char *me)
 {
 	printf("Usage: %s [-s] [-B backingstore] [-L size] [-K] [-M] [-H]\n", me);
 	printf("          [-p lxcpath] [-P newlxcpath] orig new\n");
@@ -60,6 +60,7 @@ int main(int argc, char *argv[])
 	long newsize = 0;
 	char *bdevtype = NULL, *lxcpath = NULL, *newpath = NULL, *fstype = NULL;
 	char *orig = NULL, *new = NULL, *vgname = NULL;
+	char **args = NULL;
 	char c;
 
 	if (argc < 3)
@@ -86,14 +87,13 @@ int main(int argc, char *argv[])
 		default: break;
 		}
 	}
-	if (optind == argc-2 && !orig)
+    if (optind < argc && !orig)
 		orig = argv[optind++];
-	if (optind == argc-1 && !new)
+    if (optind < argc && !new)
 		new = argv[optind++];
-	if (optind < argc) {
+	if (optind < argc)
-		printf("%d extraneous arguments\n", argc-optind);
+		/* arguments for the clone hook */
-		usage(argv[0]);
+		args = &argv[optind];
-	}
 	if (!new || !orig) {
 		printf("Error: you must provide orig and new names\n");
 		usage(argv[0]);
@@ -124,7 +124,7 @@ int main(int argc, char *argv[])
 		lxc_container_put(c1);
 		exit(1);
 	}
-	c2 = c1->clone(c1, new, newpath, flags, bdevtype, NULL, newsize);
+	c2 = c1->clone(c1, new, newpath, flags, bdevtype, NULL, newsize, args);
 	if (c2 == NULL) {
 		lxc_container_put(c1);
 		fprintf(stderr, "clone failed\n");

src/lxc/lxccontainer.c

@@ -1364,16 +1364,14 @@ static int copy_storage(struct lxc_container *c0, struct lxc_container *c,
 	return 0;
 }
 
-static int clone_update_rootfs(struct lxc_container *c, int flags)
+static int clone_update_rootfs(struct lxc_container *c, int flags, char **hookargs)
 {
 	int ret = -1;
 	char path[MAXPATHLEN];
 	struct bdev *bdev;
 	FILE *fout;
 	pid_t pid;
-
+	struct lxc_conf *conf = c->lxc_conf;
-	if (flags & LXC_CLONE_KEEPNAME)
-		return 0;
 
 	/* update hostname in rootfs */
 	/* we're going to mount, so run in a clean namespace to simplify cleanup */
@@ -1393,17 +1391,41 @@ static int clone_update_rootfs(struct lxc_container *c, int flags)
 		exit(1);
 	if (bdev->ops->mount(bdev) < 0)
 		exit(1);
-	ret = snprintf(path, MAXPATHLEN, "%s/etc/hostname", bdev->dest);
+
-	if (ret < 0 || ret >= MAXPATHLEN)
+	if (!lxc_list_empty(&conf->hooks[LXCHOOK_CLONE])) {
-		exit(1);
+		/* Start of environment variable setup for hooks */
-	if (!(fout = fopen(path, "w"))) {
+		if (setenv("LXC_NAME", c->name, 1)) {
-		SYSERROR("unable to open %s: ignoring\n", path);
+			SYSERROR("failed to set environment variable for container name");
-		exit(0);
+		}
+		if (setenv("LXC_CONFIG_FILE", conf->rcfile, 1)) {
+			SYSERROR("failed to set environment variable for config path");
+		}
+		if (setenv("LXC_ROOTFS_MOUNT", conf->rootfs.mount, 1)) {
+			SYSERROR("failed to set environment variable for rootfs mount");
+		}
+		if (setenv("LXC_ROOTFS_PATH", conf->rootfs.path, 1)) {
+			SYSERROR("failed to set environment variable for rootfs mount");
+		}
+
+		if (run_lxc_hooks(c->name, "clone", conf, hookargs)) {
+			ERROR("Error executing clone hook for %s", c->name);
+			exit(1);
+		}
+	}
+
+	if (!(flags & LXC_CLONE_KEEPNAME)) {
+		ret = snprintf(path, MAXPATHLEN, "%s/etc/hostname", bdev->dest);
+		if (ret < 0 || ret >= MAXPATHLEN)
+			exit(1);
+		if (!(fout = fopen(path, "w"))) {
+			SYSERROR("unable to open %s: ignoring\n", path);
+			exit(0);
+		}
+		if (fprintf(fout, "%s", c->name) < 0)
+			exit(1);
+		if (fclose(fout) < 0)
+			exit(1);
 	}
-	if (fprintf(fout, "%s", c->name) < 0)
-		exit(1);
-	if (fclose(fout) < 0)
-		exit(1);
 	exit(0);
 }
 
@@ -1436,7 +1458,8 @@ static int create_file_dirname(char *path)
 
 struct lxc_container *lxcapi_clone(struct lxc_container *c, const char *newname,
 		const char *lxcpath, int flags,
-		const char *bdevtype, const char *bdevdata, unsigned long newsize)
+		const char *bdevtype, const char *bdevdata, unsigned long newsize,
+		char **hookargs)
 {
 	struct lxc_container *c2 = NULL;
 	char newpath[MAXPATHLEN];
@@ -1525,7 +1548,7 @@ struct lxc_container *lxcapi_clone(struct lxc_container *c, const char *newname,
 	if (!c2->save_config(c2, NULL))
 		goto out;
 
-	if (clone_update_rootfs(c2, flags) < 0)
+	if (clone_update_rootfs(c2, flags, hookargs) < 0)
 		goto out;
 
 	// TODO: update c's lxc.snapshot = count

src/lxc/lxccontainer.h

@@ -105,7 +105,7 @@ struct lxc_container {
 	 */
 	struct lxc_container *(*clone)(struct lxc_container *c, const char *newname,
 		const char *lxcpath, int flags, const char *bdevtype,
-		const char *bdevdata, unsigned long newsize);
+		const char *bdevdata, unsigned long newsize, char **hookargs);
 
 #if 0
 	bool (*commit_cgroups)(struct lxc_container *c);

src/lxc/start.c

@@ -461,7 +461,7 @@ struct lxc_handler *lxc_init(const char *name, struct lxc_conf *conf, const char
 	}
 	/* End of environment variable setup for hooks */
 
-	if (run_lxc_hooks(name, "pre-start", conf)) {
+	if (run_lxc_hooks(name, "pre-start", conf, NULL)) {
 		ERROR("failed to run pre-start hooks for container '%s'.", name);
 		goto out_aborting;
 	}
@@ -513,7 +513,7 @@ static void lxc_fini(const char *name, struct lxc_handler *handler)
 	lxc_set_state(name, handler, STOPPING);
 	lxc_set_state(name, handler, STOPPED);
 
-	if (run_lxc_hooks(name, "post-stop", handler->conf))
+	if (run_lxc_hooks(name, "post-stop", handler->conf, NULL))
 		ERROR("failed to run post-stop hooks for container '%s'.", name);
 
 	/* reset mask set by setup_signal_fd */
@@ -676,7 +676,7 @@ static int do_start(void *data)
 	if (lxc_seccomp_load(handler->conf) != 0)
 		goto out_warn_father;
 
-	if (run_lxc_hooks(handler->name, "start", handler->conf)) {
+	if (run_lxc_hooks(handler->name, "start", handler->conf, NULL)) {
 		ERROR("failed to run start hooks for container '%s'.", handler->name);
 		goto out_warn_father;
 	}