switch-root: not only mkdir the parents but the target dir

[elogind.git] / src / core / switch-root.c

diff --git a/src/core/switch-root.c b/src/core/switch-root.c
index 150332a8587b841e8bd6a767fe6c8ce50393dbd3..0ea61dbb290f8413fba8cc0f28990bde4ca76966 100644 (file)
--- a/src/core/switch-root.c
+++ b/src/core/switch-root.c
@@ -30,6 +30,9 @@
 #include "util.h"
 #include "path-util.h"
 #include "switch-root.h"
+#include "mkdir.h"
+#include "base-filesystem.h"
+#include "missing.h"
 
 int switch_root(const char *new_root) {
 
@@ -40,20 +43,29 @@ int switch_root(const char *new_root) {
                 "/sys\0"
                 "/run\0";
 
-        int r, old_root_fd = -1;
+        _cleanup_close_ int old_root_fd = -1;
         struct stat new_root_stat;
         bool old_root_remove;
-        const char *i;
+        const char *i, *temporary_old_root;
+        int r;
 
         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 = strappenda(new_root, "/mnt");
+        mkdir_p(temporary_old_root, 0755);
+
         old_root_remove = in_initrd();
 
         if (stat(new_root, &new_root_stat) < 0) {
-                r = -errno;
                 log_error("Failed to stat directory %s: %m", new_root);
-                goto fail;
+                return -errno;
         }
 
         /* Work-around for a kernel bug: for some reason the kernel
@@ -72,6 +84,8 @@ int switch_root(const char *new_root) {
                 snprintf(new_mount, sizeof(new_mount), "%s%s", new_root, i);
                 char_array_0(new_mount);
 
+                mkdir_p(new_mount, 0755);
+
                 if ((stat(new_mount, &sb) < 0) ||
                     sb.st_dev != new_root_stat.st_dev) {
 
@@ -91,10 +105,15 @@ int switch_root(const char *new_root) {
                 }
         }
 
+        r = base_filesystem_create(new_root);
+        if (r < 0) {
+                log_error("Failed to create the base filesystem: %s", strerror(-r));
+                return r;
+        }
+
         if (chdir(new_root) < 0) {
-                r = -errno;
                 log_error("Failed to change directory to %s: %m", new_root);
-                goto fail;
+                return -errno;
         }
 
         if (old_root_remove) {
@@ -103,22 +122,31 @@ int switch_root(const char *new_root) {
                         log_warning("Failed to open root directory: %m");
         }
 
-        if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
-                r = -errno;
+        /* 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("/mnt", MNT_DETACH) < 0) {
+                        log_error("Failed to umount old root dir /mnt: %m");
+                        return -errno;
+                }
+
+        } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
                 log_error("Failed to mount moving %s to /: %m", new_root);
-                goto fail;
+                return -errno;
         }
 
         if (chroot(".") < 0) {
-                r = -errno;
                 log_error("Failed to change root: %m");
-                goto fail;
+                return -errno;
         }
 
         if (chdir("/") < 0) {
-                r = -errno;
                 log_error("Failed to change directory: %m");
-                goto fail;
+                return -errno;
         }
 
         if (old_root_fd >= 0) {
@@ -132,11 +160,5 @@ int switch_root(const char *new_root) {
                 }
         }
 
-        r = 0;
-
-fail:
-        if (old_root_fd >= 0)
-                close_nointr_nofail(old_root_fd);
-
-        return r;
+        return 0;
 }