[CRIU] [PATCH v2 3/5] mount: save ext_real_root for external mounts

[Pavel Tikhomirov]

On 03/23/2017 11:36 AM, Pavel Emelyanov wrote:
> On 03/21/2017 10:53 AM, Pavel Tikhomirov wrote:
>>
>>
>> On 03/20/2017 10:03 PM, Andrew Vagin wrote:
>>> On Mon, Mar 20, 2017 at 12:45:42PM +0300, Pavel Tikhomirov wrote:
>>>> need it to check if we can bindmount from external mount
>>>>
>>>> https://jira.sw.ru/browse/PSBM-46753
>>>>
>>>> v2: s/real_root/ext_real_root/
>>>> Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
>>>> ---
>>>>  criu/mount.c     | 3 ++-
>>>>  images/mnt.proto | 1 +
>>>>  2 files changed, 3 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/criu/mount.c b/criu/mount.c
>>>> index 6e5a4c6..ef5c1ec 100644
>>>> --- a/criu/mount.c
>>>> +++ b/criu/mount.c
>>>> @@ -1335,6 +1335,7 @@ static int dump_one_mountpoint(struct mount_info *pm, struct cr_img *img)
>>>>  		 * for reverse mapping details.
>>>>  		 */
>>>>  		me.root	= pm->external;
>>>> +		me.ext_real_root = pm->root;
>>>>  		me.has_ext_mount = true;
>>>>  		me.ext_mount = true;
>>>>  	} else
>>>> @@ -2445,7 +2446,7 @@ static int get_mp_root(MntEntry *me, struct mount_info *mi)
>>>>  {
>>>>  	char *ext = NULL;
>>>>
>>>> -	mi->root = xstrdup(me->root);
>>>> +	mi->root = xstrdup(me->ext_real_root ? : me->root);
>>>>  	if (!mi->root)
>>>>  		return -1;
>>>>
>>>> diff --git a/images/mnt.proto b/images/mnt.proto
>>>> index 50cd8af..3294319 100644
>>>> --- a/images/mnt.proto
>>>> +++ b/images/mnt.proto
>>>> @@ -53,4 +53,5 @@ message mnt_entry {
>>>>
>>>>  	optional bool		deleted			= 16;
>>>>  	optional uint32		sb_flags		= 17 [(criu).hex = true];
>>>> +	optional string		ext_real_root		= 18;
>>>
>>> We need a comment here what this means. What do you think if we add
>>> ext_key instead of ext_real_root, for me it looks more understandable.
>>
>> If we use me->root for real root, and me->ext_key for the key of the
>> mount, that would surely break backward compatibility, as old criu will
>> still want the key in me->root.
>
> There's no need in letting older criu restore stuff from newer images.
> If we think that the existing field should be used the other way, then
> rename it to ${old_name}_deprecated in the image, introduce the new one
> and always use it.

Please, see "[PATCH v5 1/3] mount: save ext_real_root for external mounts"

I've resent the patchset, and in v5 I made mnt_entry->root always show 
root - no more mapping in it. And at the same time mnt_entry->ext_mount 
will always be false, so that old criu will just see no external mounts 
provided in new image. So no need to deprecate mnt_entry->root, we can 
reuse it.

Now external mount mapping is determined on me->ext_key field check, so 
I need ext_mount only for forward compatibility, we can deprecate it 
later if needed.

>
>> Thus we should leave the key of the mount in me->root. And naming the
>> field in which I want to save the real root(path in the file system to
>> the root of these mount) as me->ext_key is counterintuitive to me.
>>
>>>>  }
>>>> --
>>>> 2.9.3
>>>>
>>
>

-- 
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.