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-rw-r--r--src/core/switch-root.c27
1 files changed, 26 insertions, 1 deletions
diff --git a/src/core/switch-root.c b/src/core/switch-root.c
index 150332a858..ce0e41d510 100644
--- a/src/core/switch-root.c
+++ b/src/core/switch-root.c
@@ -30,6 +30,7 @@
#include "util.h"
#include "path-util.h"
#include "switch-root.h"
+#include "missing.h"
int switch_root(const char *new_root) {
@@ -44,10 +45,21 @@ int switch_root(const char *new_root) {
struct stat new_root_stat;
bool old_root_remove;
const char *i;
+ _cleanup_free_ char *temporary_old_root = NULL;
if (path_equal(new_root, "/"))
return 0;
+ /* When using pivot_root() we assume that /mnt exists as place
+ * we can temporarily move the old root to. As we immediately
+ * unmount it from there it doesn't matter much which
+ * directory we choose for this, but it should be more likely
+ * than not that /mnt exists and is suitable as mount point
+ * and is on the same fs as the old root dir */
+ temporary_old_root = strappend(new_root, "/mnt");
+ if (!temporary_old_root)
+ return -ENOMEM;
+
old_root_remove = in_initrd();
if (stat(new_root, &new_root_stat) < 0) {
@@ -103,7 +115,20 @@ int switch_root(const char *new_root) {
log_warning("Failed to open root directory: %m");
}
- if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
+ /* We first try a pivot_root() so that we can umount the old
+ * root dir. In many cases (i.e. where rootfs is /), that's
+ * not possible however, and hence we simply overmount root */
+ if (pivot_root(new_root, temporary_old_root) >= 0) {
+
+ /* Immediately get rid of the old root. Since we are
+ * running off it we need to do this lazily. */
+ if (umount2(temporary_old_root, MNT_DETACH) < 0) {
+ r = -errno;
+ log_error("Failed to umount old root dir %s: %m", temporary_old_root);
+ goto fail;
+ }
+
+ } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
r = -errno;
log_error("Failed to mount moving %s to /: %m", new_root);
goto fail;