[CRIU] [PATCH v4 3/3] mount: Restore binfmt_misc content in case of missing mount

[Pavel Emelyanov]

On 08/02/2016 11:06 PM, Andrew Vagin wrote:
> On Tue, Aug 02, 2016 at 04:41:54PM +0300, Kirill Tkhai wrote:
>>
>>
>> On 02.08.2016 16:39, Pavel Emelyanov wrote:
>>> On 08/02/2016 04:29 PM, Kirill Tkhai wrote:
>>>>
>>>>
>>>> On 02.08.2016 16:03, Pavel Emelyanov wrote:
>>>>> On 07/20/2016 01:13 PM, Kirill Tkhai wrote:
>>>>>> In case of mount image is not containing binfmt_misc mountpoint,
>>>>>> scan image directory for binfmt_misc content file (binfmt-misc-xxx).
>>>>>> If a file is found, add temporary mountpoint to mount tree and
>>>>>> restore the content in ordinary way. Then, umount temporary mountpoint.
>>>>>>
>>>>>> v4: New
>>>>>>
>>>>>> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
>>>>>> ---
>>>>>>  criu/mount.c |   61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>>>>>>  1 file changed, 59 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/criu/mount.c b/criu/mount.c
>>>>>> index d583429..8657c36 100644
>>>>>> --- a/criu/mount.c
>>>>>> +++ b/criu/mount.c
>>>>>> @@ -1379,6 +1379,39 @@ static int try_mount_binfmt_misc(struct ns_id *ns, unsigned int *s_dev)
>>>>>>  	return ret ? -1 : exit_code;
>>>>>>  }
>>>>>>  
>>>>>> +static int find_binfmt_misc_img(unsigned int *s_dev)
>>>>>> +{
>>>>>> +	struct dirent *de;
>>>>>> +	int dfd, ret;
>>>>>> +	DIR *dir;
>>>>>> +
>>>>>> +	*s_dev = 0;
>>>>>> +	dfd = dup(get_service_fd(IMG_FD_OFF));
>>>>>> +	dir = fdopendir(dfd);
>>>>>> +	if (!dir) {
>>>>>> +		close(dfd);
>>>>>> +		pr_perror("Can't open img dir\n");
>>>>>> +		return -1;
>>>>>> +	}
>>>>>> +	rewinddir(dir);
>>>>>> +
>>>>>> +	errno = 0;
>>>>>> +	while ((de = readdir(dir)) != NULL) {
>>>>>
>>>>> Scanning the images dir doesn't look valid. Instead, there should be a proper
>>>>> collection of this image (like we do with fdinfo-s, sockets and others). Then,
>>>>> when reading the mountpoint images, the binfmt_misc collected data should be
>>>>> looked up and orphan data should add the cr-time mountpoints.
>>>>
>>>> So, for every type you want to make array of images, don't you?
>>>
>>> What do you mean?
>>
>> Introduce a new type of objects, "dump images". And collect names of images,
>> like we do for other object types.
>>
>> As I understand right, you want so.
> 
>         img = open_image(CR_FD_BINFMT_MISC, O_DUMP, pm->s_dev);
> 
> I think we choose a wrong format for an image name here.

Agree. Since binfmt entries exist w/o any mountpoints, then ID of the
image with entries should be some other, not the device.

Another option would be to put __all__ binfmt-s into single file w/o any
IDs in name. Like binfmts.img. And on restore collect one and cache.

> binfmt_misc is a property of a container (the ve structure). If someone
> will containerize it in the upstream kernel, it probably will be a
> property of a mount namespace. I suggest to use mntns->id instead of
> pm->s_dev for binfmt images.