Daniel Lezcano <daniel.lezc...@free.fr> writes:
> Ferenc Wagner wrote:
>
>> Ferenc Wagner <wf...@niif.hu> writes:
>>
>>> Daniel Lezcano <dlezc...@fr.ibm.com> writes:
>>>
>>>> Ferenc Wagner wrote:
>>>>
>>>>> Daniel Lezcano <daniel.lezc...@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.
>>
>> From 98b24c13f809f18ab8969fb4d84defe6f812b25c Mon Sep 17 00:00:00 2001
>> From: Ferenc Wagner <wf...@niif.hu>
>> Date: Thu, 6 May 2010 14:47:39 +0200
>> Subject: [PATCH] no need to use a temporary directory for pivoting
>> [...]
>
> 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."
Hmm, this could indeed be a problem if lxc.rootfs is on the current root
file system. I didn't consider pivoting to the same FS, but looks like
this is the very reason for the current complexity in the architecture.
Btw. is this really a safe thing to do, to pivot into a subdirectory of
a file system? Is there really no way out of that?
> But as we will pivot_root right after, we won't reuse the real rootfs,
> so we can safely use the host /tmp.
That will cause problems if rootfs is under /tmp, don't you think?
Actually, I'm not sure you can fully solve this. If rootfs is a
separate file system, this is only much ado about nothing. If rootfs
isn't a separate filesystem, you can't automatically find a good place
and also clean it up. So why not require that rootfs is a separate
filesystem, and let the user deal with it by doing the necessary bind
mount in the lxc config?
> --- lxc.orig/src/lxc/conf.c
> +++ lxc/src/lxc/conf.c
> @@ -581,37 +581,24 @@ static int setup_rootfs_pivot_root(const
>
> static int setup_rootfs(const char *rootfs, const char *pivotdir)
> {
> - char *tmpname;
> - int ret = -1;
> + const char *tmpfs = "/tmp";
>
> if (!rootfs)
> return 0;
>
> - tmpname = tempnam("/tmp", "lxc-rootfs");
> - if (!tmpname) {
> - SYSERROR("failed to generate temporary name");
> + if (mount(rootfs, tmpfs, "none", MS_BIND|MS_REC, NULL)) {
> + SYSERROR("failed to mount '%s'->'%s'", rootfs, "/tmp");
You probably meant tmpfs instead of "/tmp" in SYSERROR() above.
--
Thanks,
Feri.
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