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

[Harald Hoyer <harald-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

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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