[Lxc-users] lxc-start leaves temporary pivot dir behind

[Daniel Lezcano]

Ferenc Wagner wrote:
> Ferenc Wagner <wferi at niif.hu> writes:
>
>   
>> Daniel Lezcano <dlezcano at fr.ibm.com> writes:
>>
>>     
>>> Ferenc Wagner wrote:
>>>
>>>       
>>>> Daniel Lezcano <daniel.lezcano at free.fr> writes:
>>>>
>>>>         
>>>>> Ferenc Wagner wrote:
>>>>>
>>>>>           
>>>>>> While playing with lxc-start, I noticed that /tmp is infested by
>>>>>> empty lxc-r* directories: [...] Ok, this name comes from lxc-rootfs
>>>>>> in conf.c:setup_rootfs.  After setup_rootfs_pivot_root returns, the
>>>>>> original /tmp is not available anymore, so rmdir(tmpname) at the
>>>>>> bottom of setup_rootfs can't achieve much.  Why is this temporary
>>>>>> name needed anyway?  Is pivoting impossible without it?
>>>>>>             
>>>>> That was put in place with chroot, before pivot_root, so the distro's
>>>>> scripts can remount their '/' without failing.
>>>>>
>>>>> Now we have pivot_root, I suppose we can change that to something cleaner...
>>>>>           
>>>> Like simply nuking it?  Shall I send a patch?
>>>>         
>>> Sure, if we can kill it, I will be glad to take your patch :)
>>>       
>> I can't see any reason why lxc-start couldn't do without that temporary
>> recursive bind mount of the original root.  If neither do you, I'll
>> patch it out and see if it still flies.
>>     
>
> For my purposes the patch below works fine.  I only run applications,
> though, not full systems, so wider testing is definitely needed.
>
> Thanks,
> Feri.
>
> >From 98b24c13f809f18ab8969fb4d84defe6f812b25c Mon Sep 17 00:00:00 2001
> From: Ferenc Wagner <wferi at niif.hu>
> Date: Thu, 6 May 2010 14:47:39 +0200
> Subject: [PATCH] no need to use a temporary directory for pivoting
>
> That was put in place before lxc-start started using pivot_root, so
> the distro scripts can remount / without problems.
>
> Signed-off-by: Ferenc Wagner <wferi at niif.hu>
> ---
>  src/lxc/conf.c |   28 +++-------------------------
>  1 files changed, 3 insertions(+), 25 deletions(-)
>
> diff --git a/src/lxc/conf.c b/src/lxc/conf.c
> index b27a11d..4379a32 100644
> --- a/src/lxc/conf.c
> +++ b/src/lxc/conf.c
> @@ -588,37 +588,15 @@ static int setup_rootfs_pivot_root(const char *rootfs, const char *pivotdir)
>  
>  static int setup_rootfs(const char *rootfs, const char *pivotdir)
>  {
> -	char *tmpname;
> -	int ret = -1;
> -
>  	if (!rootfs)
>  		return 0;
>  
> -	tmpname = tempnam("/tmp", "lxc-rootfs");
> -	if (!tmpname) {
> -		SYSERROR("failed to generate temporary name");
> -		return -1;
> -	}
> -
> -	if (mkdir(tmpname, 0700)) {
> -		SYSERROR("failed to create temporary directory '%s'", tmpname);
> -		return -1;
> -	}
> -
> -	if (mount(rootfs, tmpname, "none", MS_BIND|MS_REC, NULL)) {
> -		SYSERROR("failed to mount '%s'->'%s'", rootfs, tmpname);
> -		goto out;
> -	}
> -
> -	if (setup_rootfs_pivot_root(tmpname, pivotdir)) {
> +	if (setup_rootfs_pivot_root(rootfs, pivotdir)) {
>  		ERROR("failed to pivot_root to '%s'", rootfs);
> -		goto out;
> +		return -1;
>  	}
>  
> -	ret = 0;
> -out:
> -	rmdir(tmpname);
> -	return ret;
> +	return 0;
>  }
>  
>  static int setup_pts(int pts)
>   

We can't simply remove it because of the pivot_root which returns EBUSY.

I suppose it's coming from:
"new_root and put_old must not be on the same file system as the current 
root."

But as we will pivot_root right after, we won't reuse the real rootfs, 
so we can safely use the host /tmp.

I tried the following patch and it worked.

Comments ?



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