[CRIU] Sync TODO-s for mount.c work

[Pavel Emelyanov]

On 04/23/2015 07:05 PM, Tycho Andersen wrote:
> On Thu, Apr 23, 2015 at 06:51:26PM +0300, Pavel Emelyanov wrote:
>> On 04/23/2015 06:09 PM, Tycho Andersen wrote:
>>> On Thu, Apr 23, 2015 at 06:04:35PM +0300, Pavel Emelyanov wrote:
>>>> On 04/23/2015 05:31 PM, Tycho Andersen wrote:
>>>>> On Thu, Apr 23, 2015 at 02:52:35PM +0300, Pavel Emelyanov wrote:
>>>>>> On 04/23/2015 02:17 PM, Oleg Nesterov wrote:
>>>>>>
>>>>>>> Now what? Obviously we can't just add
>>>>>>>
>>>>>>> 	if (is_not_external_mount(m))
>>>>>>> 		continue;
>>>>>>
>>>>>> Why not? The is_not_external_mount() is
>>>>>>
>>>>>> fsroot_mounted(m) || /* mount's root is visible from chroot */
>>>>>
>>>>> But what if the mount's root is /? e.g with pstore in lxc, the
>>>>> mountinfo from inside looks like:
>>>>>
>>>>> 110 104 0:23 / /sys/fs/pstore rw,nosuid,nodev,noexec,relatime master:11 - pstore pstore rw
>>>>>
>>>>> which is a bind mount from the host's:
>>>>>
>>>>> 29 17 0:23 / /sys/fs/pstore rw,nosuid,nodev,noexec,relatime shared:11 - pstore pstore rw
>>>>
>>>> Ah, so sharing takes place. OK, then (sorry, maybe I'm replaying your
>>>> conversation again, but I'm still blind about it) the check should be
>>>>
>>>>    (fsroot_mounted(m) || root_is_visible(m)) && master_is_external(m)
>>>
>>> I think not, because if we didn't have this as a shared mount it would
>>> still be an external bind mount, just without sharing. An external
>>> master peer is an indication that it's a bind mount, but if we don't
>>> have one of those, it could still be a bind mount.
>>
>> Ah, sure. It should be NOT before master_is_external, like this
>>
>>    (fsroot_mounted(m) || root_is_visible(m)) && !master_is_external()
>>
>> Provided master_is_external() is false for private mounts, this should
>> handle Oleg's case with mount --make-rprivate, but in suboptimal way --
>> all mountpoints will be bind-mounted from host with MS_SLAVE flag.
> 
> But this only works for mounts that have external masters. Doesn't it
> fail to exclude mounts which aren't in a peer group at all (since
> !master_is_external() will always be true for them)?

Yes, !master_is_external() will be true and then the 2nd part of the
check will take place -- fsroot || root_is_visible. If _this_ will be
false then mountpoint will be still considered to be external.

-- Pavel