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

[Peter Jones <pjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

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.

-- 
        Peter

Any connection between your reality and mine is purely coincidental.