82 lines
3.3 KiB
Diff
82 lines
3.3 KiB
Diff
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From 891a4918ef75fa81e22691156c050d061bd53dd3 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Fri, 16 Nov 2012 18:15:30 +0100
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Subject: [PATCH] switch-root: try pivot_root() before overmounting /
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We should always try to umount the old root dir if possible, instead of
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overmounting it -- if that's possible.
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The initial ("first") kernel rootfs can never be umounted, hence
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for the usual nitrd case we never bothered using pivot_root() and
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hence with fully unmounting it. However, fedup now tranisitions twice
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during boot, and in that case it is highly desirable that the "second"
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root dir is entirely unmounted when we switch to the "third". This patch
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makes that possible.
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The pivot_root() needs a directory in the "third" root dir, to move the
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"second" root dir to. We use /mnt for that, under the assumption that
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this directory is likely to exist, and is not itself a mount point.
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---
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src/core/switch-root.c | 27 ++++++++++++++++++++++++++-
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1 file changed, 26 insertions(+), 1 deletion(-)
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diff --git a/src/core/switch-root.c b/src/core/switch-root.c
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index 150332a..ce0e41d 100644
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--- a/src/core/switch-root.c
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+++ b/src/core/switch-root.c
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@@ -30,6 +30,7 @@
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#include "util.h"
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#include "path-util.h"
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#include "switch-root.h"
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+#include "missing.h"
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int switch_root(const char *new_root) {
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@@ -44,10 +45,21 @@ int switch_root(const char *new_root) {
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struct stat new_root_stat;
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bool old_root_remove;
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const char *i;
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+ _cleanup_free_ char *temporary_old_root = NULL;
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if (path_equal(new_root, "/"))
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return 0;
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+ /* When using pivot_root() we assume that /mnt exists as place
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+ * we can temporarily move the old root to. As we immediately
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+ * unmount it from there it doesn't matter much which
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+ * directory we choose for this, but it should be more likely
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+ * than not that /mnt exists and is suitable as mount point
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+ * and is on the same fs as the old root dir */
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+ temporary_old_root = strappend(new_root, "/mnt");
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+ if (!temporary_old_root)
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+ return -ENOMEM;
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+
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old_root_remove = in_initrd();
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if (stat(new_root, &new_root_stat) < 0) {
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@@ -103,7 +115,20 @@ int switch_root(const char *new_root) {
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log_warning("Failed to open root directory: %m");
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}
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- if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
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+ /* We first try a pivot_root() so that we can umount the old
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+ * root dir. In many cases (i.e. where rootfs is /), that's
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+ * not possible however, and hence we simply overmount root */
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+ if (pivot_root(new_root, temporary_old_root) >= 0) {
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+
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+ /* Immediately get rid of the old root. Since we are
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+ * running off it we need to do this lazily. */
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+ if (umount2(temporary_old_root, MNT_DETACH) < 0) {
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+ r = -errno;
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+ log_error("Failed to umount old root dir %s: %m", temporary_old_root);
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+ goto fail;
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+ }
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+
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+ } else if (mount(new_root, "/", NULL, MS_MOVE, NULL) < 0) {
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r = -errno;
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log_error("Failed to mount moving %s to /: %m", new_root);
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goto fail;
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--
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1.7.10.4
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