[lxc-devel] Patch: pivot_root, new version

Michael Holzt lxc at my.fqdn.org
Wed Jan 6 04:14:24 UTC 2010


> please find attached a rewritten and cleaned up version of my pivot_root
> patch.

Regretfully the patch contained two errors. Please see fixed version
attached.

Regards,
Michael

-- 
It's an insane world, but i'm proud to be a part of it. -- Bill Hicks
-------------- next part --------------
diff -Naur lxc-0.6.4/src/lxc/conf.c lxc-0.6.4-pivot/src/lxc/conf.c
--- lxc-0.6.4/src/lxc/conf.c	2009-11-24 09:47:26.000000000 +0100
+++ lxc-0.6.4-pivot/src/lxc/conf.c	2010-01-06 05:10:46.000000000 +0100
@@ -65,6 +65,8 @@
 #define MS_REC 16384
 #endif
 
+extern int pivot_root(const char * new_root, const char * put_old);
+
 typedef int (*instanciate_cb)(struct lxc_netdev *);
 
 struct mount_opt {
@@ -334,7 +336,145 @@
 	return 0;
 }
 
-static int setup_rootfs(const char *rootfs)
+static int setup_rootfs_pivot_root_cb(char *mountentry, void **data)
+{
+	struct lxc_list	*mountlist, *listentry, *iterator;
+	char *pivotdir, *mountpoint;
+	int found;
+	
+	mountlist = data[0];
+	pivotdir  = data[1];
+
+	/* parse entry, first field is mountname, ignore */	
+	mountpoint = strtok(mountentry, " ");
+	if (!mountpoint)
+		return -1;
+	
+	/* second field is mountpoint */
+	mountpoint = strtok(NULL, " ");
+	if (!mountpoint)
+		return -1;
+
+	/* only consider mountpoints below old root fs */
+	if (strncmp(mountpoint, pivotdir, strlen(pivotdir)))
+		return 0;
+		
+	/* filter duplicate mountpoints */
+	found = 0;
+	lxc_list_for_each(iterator, mountlist) {
+		if (!strcmp(iterator->elem, mountpoint))
+			found = 1;
+	}
+	if (found)
+		return 0;
+		
+	/* add entry to list */
+	listentry = malloc(sizeof(*listentry));
+	if (!listentry) {
+		SYSERROR("malloc for mountpoint listentry failed");
+		return -1;
+	}
+	
+	listentry->elem = strdup(mountpoint);
+	lxc_list_add_tail(mountlist, listentry);
+	
+	return 0;
+}
+
+
+static int setup_rootfs_pivot_root(const char *rootfs, const char *pivotdir)
+{
+	char path[MAXPATHLEN], buffer[MAXPATHLEN];
+	void *cbparm[2];
+	struct lxc_list mountlist, *iterator;
+	int ok, still_mounted, last_still_mounted;
+
+	/* pivot_root into our new root fs */
+	snprintf(path, sizeof(path), ".%s", pivotdir);
+
+	chdir(rootfs);
+	if (pivot_root(".", path)) {
+		SYSERROR("pivot_root syscall failed");
+		return -1;
+	}
+	chdir("/");
+	DEBUG("pivot_root syscall successful");
+	
+	/* read and parse /proc/mounts in old root fs */
+	lxc_list_init(&mountlist);
+
+	snprintf(path, sizeof(path), "%s/", pivotdir);
+	cbparm[0] = &mountlist;
+	cbparm[1] = strdup(path);
+
+	snprintf(path, sizeof(path), "/%s/proc/mounts", pivotdir);
+	ok = lxc_file_for_each_line(path,
+			       setup_rootfs_pivot_root_cb,
+			       buffer, sizeof(buffer), &cbparm);
+	if (ok < 0) {
+		SYSERROR("failed to read or parse mount list '%s'", path);
+		return -1;
+	}
+
+	/* umount filesystems until none left or list no longer shrinks */
+	still_mounted = 0;
+	do {
+		last_still_mounted = still_mounted;
+		still_mounted = 0;
+		
+		lxc_list_for_each(iterator, &mountlist) {
+			ok = umount(iterator->elem);
+			
+			if (!ok) {
+				DEBUG("umounted '%s'", iterator->elem);
+				lxc_list_del(iterator);
+			}
+			else {
+				if (errno != EBUSY) {
+					SYSERROR("failed to umount '%s'", iterator->elem);
+					return -1;
+				}
+
+				still_mounted++;
+			}
+		}
+	} while (still_mounted > 0 && still_mounted != last_still_mounted);
+	
+	if (still_mounted) {
+		ERROR("could not umount %d mounts", still_mounted);
+		return -1;
+	}
+
+	/* umount old root fs */
+	if (umount(pivotdir)) {
+		SYSERROR("could not unmount old rootfs");
+		return -1;
+	}
+	DEBUG("umounted '%s'", pivotdir);
+	
+
+	INFO("pivoted to '%s'", rootfs);
+	return 0;
+}	
+
+static int setup_rootfs_chroot(const char *rootfs)
+{
+	if (chroot(rootfs)) {
+		SYSERROR("failed to set chroot %s", rootfs);
+		return -1;
+	}
+
+	if (chdir(getenv("HOME")) && chdir("/")) {
+		SYSERROR("failed to change to home directory");
+		return -1;
+	}
+
+	INFO("chrooted to '%s'", rootfs);
+	return 0;
+}
+
+
+static int setup_rootfs(const char *rootfs, const char *pivotdir)
 {
 	char *tmpname;
 	int ret = -1;
@@ -358,18 +498,16 @@
 		goto out;
 	}
 
-	if (chroot(tmpname)) {
-		SYSERROR("failed to set chroot %s", tmpname);
-		goto out;
+        if (pivotdir && setup_rootfs_pivot_root(tmpname, pivotdir)) {
+       		ERROR("failed to pivot_root to '%s' (put_old: '%s')", rootfs, pivotdir);
+       		goto out;
 	}
 
-	if (chdir(getenv("HOME")) && chdir("/")) {
-		SYSERROR("failed to change to home directory");
+	if (!pivotdir && setup_rootfs_chroot(tmpname)) {
+		ERROR("failed to chroot to '%s'", rootfs);
 		goto out;
 	}
-
-	INFO("chrooted to '%s'", rootfs);
-
+	
 	ret = 0;
 out:
 	rmdir(tmpname);
@@ -816,6 +954,7 @@
 int lxc_conf_init(struct lxc_conf *conf)
 {
 	conf->rootfs = NULL;
+	conf->pivotdir = NULL;
 	conf->fstab = NULL;
 	conf->utsname = NULL;
 	conf->tty = 0;
@@ -1086,7 +1225,7 @@
 		return -1;
 	}
 
-	if (setup_rootfs(lxc_conf->rootfs)) {
+	if (setup_rootfs(lxc_conf->rootfs, lxc_conf->pivotdir)) {
 		ERROR("failed to set rootfs for '%s'", name);
 		return -1;
 	}
diff -Naur lxc-0.6.4/src/lxc/conf.h lxc-0.6.4-pivot/src/lxc/conf.h
--- lxc-0.6.4/src/lxc/conf.h	2009-11-19 15:06:02.000000000 +0100
+++ lxc-0.6.4-pivot/src/lxc/conf.h	2010-01-06 05:10:18.000000000 +0100
@@ -133,6 +133,7 @@
  */
 struct lxc_conf {
 	char *rootfs;
+	char *pivotdir;
 	char *fstab;
 	int tty;
 	int pts;
@@ -167,6 +168,7 @@
 
 #define conf_has_fstab(__name)   conf_has(__name, "fstab")
 #define conf_has_rootfs(__name)  conf_has(__name, "rootfs")
+#define conf_has_pivotdir(__name) conf_has(__name, "pivotdir")
 #define conf_has_utsname(__name) conf_has(__name, "utsname")
 #define conf_has_network(__name) conf_has(__name, "network")
 #define conf_has_console(__name) conf_has(__name, "console")
diff -Naur lxc-0.6.4/src/lxc/confile.c lxc-0.6.4-pivot/src/lxc/confile.c
--- lxc-0.6.4/src/lxc/confile.c	2009-11-19 15:06:02.000000000 +0100
+++ lxc-0.6.4-pivot/src/lxc/confile.c	2010-01-06 03:16:45.000000000 +0100
@@ -44,6 +44,7 @@
 static int config_cgroup(const char *, char *, struct lxc_conf *);
 static int config_mount(const char *, char *, struct lxc_conf *);
 static int config_rootfs(const char *, char *, struct lxc_conf *);
+static int config_pivotdir(const char *, char *, struct lxc_conf *);
 static int config_utsname(const char *, char *, struct lxc_conf *);
 static int config_network_type(const char *, char *, struct lxc_conf *);
 static int config_network_flags(const char *, char *, struct lxc_conf *);
@@ -68,6 +69,7 @@
 	{ "lxc.cgroup",         config_cgroup         },
 	{ "lxc.mount",          config_mount          },
 	{ "lxc.rootfs",         config_rootfs         },
+	{ "lxc.pivotdir",	config_pivotdir       },
 	{ "lxc.utsname",        config_utsname        },
 	{ "lxc.network.type",   config_network_type   },
 	{ "lxc.network.flags",  config_network_flags  },
@@ -494,6 +496,22 @@
 	return 0;
 }
 
+static int config_pivotdir(const char *key, char *value, struct lxc_conf *lxc_conf)
+{
+	if (strlen(value) >= MAXPATHLEN) {
+		ERROR("%s path is too long", value);
+		return -1;
+	}
+
+	lxc_conf->pivotdir = strdup(value);
+	if (!lxc_conf->rootfs) {
+		SYSERROR("failed to duplicate string %s", value);
+		return -1;
+	}
+
+	return 0;
+}
+
 static int config_utsname(const char *key, char *value, struct lxc_conf *lxc_conf)
 {
 	struct utsname *utsname;


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