Re: [PATCH] switch_root: a better approach to subroots

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On 11/18/2009 09:13 PM, Peter Jones wrote:
On 11/18/2009 01:47 PM, Karel Zak wrote:

  I think dracut guys should be in CC. Any objection against this change?

On Wed, Nov 18, 2009 at 03:33:12PM +0000, Daniel Drake wrote:
This reverts commit a692a8745941a192528c5e2a05de97155ba586f9.
Booting into a system this way just leads to problems because
you cannot remount the root read-only at shutdown (leading to unclean
shutdowns).

Miklos Szeredi pointed out a trick to turn any directory into a
mount point which avoids this problem. Therefore we can simplify
switch_root again and simply document that its users should set
up the root as a mount point beforehand.
---
  sys-utils/switch_root.8 |   13 +++++++
  sys-utils/switch_root.c |   81 +++--------------------------------------------
  2 files changed, 18 insertions(+), 76 deletions(-)

diff --git a/sys-utils/switch_root.8 b/sys-utils/switch_root.8
index 4fdc8e9..b6712ec 100644
--- a/sys-utils/switch_root.8
+++ b/sys-utils/switch_root.8
@@ -32,6 +32,19 @@ show version number and exit
  .B switch_root
  returns 0 on success and 1 on failure.

+.SH NOTES
+switch_root will fail to function if
+.B newroot
+is not the root of a mount. If you want to switch root into a directory that
+does not meet this requirement then you can first use a bind-mounting trick to
+turn any directory into a mount point:
+.sp
+.nf
+.RS
+mount --bind $DIR $DIR

  Cannot we add this functionality directly to the switch_root command?
  I mean call:

     mount --bind /newroot/subroot /newroot/subroot
     mount --move /newroot/subroot /

  Now we have:

     mount --move newroot /
     chroot /newroot/subroot

That certainly seems preferable to reverting the patch, especially if, as
the original commit log says, some distro (OLPC in this case) is actually
using this functionality.


no objections
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