fix pivot_root temporary directory

First of all, when trying to start a container in a read-only root lxc-start complains: lxc-start: Read-only file system - can't make temporary mountpoint This is in conf.c:setup_rootfs_pivot_root() function. That function uses optional parameter "lxc.pivotdir", or creates (and later removes) a temporary directory for pivot_root. Obviously there's no way to create a directory in a read-only filesystem. But lxc.pivotdir does not work either. In the function mentioned above it is used with leading dot (eg. if I specify "lxc.pivotdir=pivot" in the config file the pivot_root() syscall will be made to ".pivot" with leading dot, not to "pivot"), but later on it is used without that dot, and fails: lxc-start: No such file or directory - failed to open /pivot/proc/mounts lxc-start: No such file or directory - failed to read or parse mount list '/pivot/proc/mounts' lxc-start: failed to pivot_root to '/stage/t' (that's with "lxc.pivotdir = pivot" in the config file). After symlinking pivot to .pivot it still fails: lxc-start: Device or resource busy - could not unmount old rootfs lxc-start: failed to pivot_root to '/stage/t' Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com> Reported-by: Michael Tokarev <mjt@tls.msk.ru>

fix pivot_root temporary directory
1b09f2c0 · Daniel Lezcano · Daniel Lezcano · 5c294060 · 1b09f2c0 · 1b09f2c0
Commit 1b09f2c0 authored May 10, 2010 by Daniel Lezcano Committed by Daniel Lezcano May 10, 2010
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Showing with 46 additions and 8 deletions

conf.c src/lxc/conf.c +17 -8

utils.c src/lxc/utils.c +28 -0

utils.h src/lxc/utils.h +1 -0

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--- a/src/lxc/conf.c
+++ b/src/lxc/conf.c
@@ -51,10 +51,10 @@
 #include "error.h"
 #include "parse.h"
 #include "config.h"
+#include "utils.h"
-#include <lxc/conf.h>
+#include "conf.h"
-#include <lxc/log.h>
+#include "log.h"
-#include <lxc/lxc.h>	/* for lxc_cgroup_set() */
+#include "lxc.h"	/* for lxc_cgroup_set() */
 lxc_log_define(lxc_conf, lxc);
@@ -488,12 +488,21 @@ static int setup_rootfs_pivot_root(const char *rootfs, const char *pivotdir)
 		}
 		pivotdir_is_temp = 1;
-	}
+	} else {
-	else {
-		snprintf(path, sizeof(path), ".%s", pivotdir);
+		snprintf(path, sizeof(path), "%s/%s", rootfs, pivotdir);
+		if (access(path, F_OK)) {
+			if (mkdir_p(path, 0755)) {
+				SYSERROR("failed to create pivotdir '%s'", path);
+				return -1;
+			}
+			DEBUG("created '%s' directory", path);
+		}
 	}
-	DEBUG("temporary mountpoint for old rootfs is '%s'", path);
+	DEBUG("mountpoint for old rootfs is '%s'", path);
 	/* pivot_root into our new root fs */

--- a/src/lxc/utils.c
+++ b/src/lxc/utils.c
@@ -33,6 +33,7 @@
 #include <sys/mount.h>
 #include <dirent.h>
 #include <fcntl.h>
+#include <libgen.h>
 #include "log.h"
@@ -163,3 +164,30 @@ extern int get_u16(ushort *val, const char *arg, int base)
 	return 0;
 }
+extern int mkdir_p(char *dir, mode_t mode)
+{
+        int ret;
+        char *d;
+        if (!strcmp(dir, "/"))
+                return 0;
+        d = strdup(dir);
+        if (!d)
+                return -1;
+        ret = mkdir_p(dirname(d), mode);
+        free(d);
+        if (ret)
+                return -1;
+        if (!access(dir, F_OK))
+                return 0;
+        if (mkdir(dir, mode)) {
+                SYSERROR("failed to create directory '%s'\n", dir);
+                return -1;
+        }
+        return 0;
+}
--- a/src/lxc/utils.h
+++ b/src/lxc/utils.h
@@ -53,3 +53,4 @@
 extern int lxc_copy_file(const char *src, const char *dst);
 extern int lxc_setup_fs(void);
 extern int get_u16(ushort *val, const char *arg, int base);
+extern int mkdir_p(const char *dir, mode_t mode);