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

[Kirill Tkhai]

On 02.08.2016 23:06, 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.
> 
> 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.

It's probably, but not 100%. Implementations may be different. It may be,
someone will implement something like ct_ns.

>>
>>  
>>>>>
>>>>>> +		if (strncmp(de->d_name, "binfmt-misc-", 12) == 0) {
>>>>>> +			*s_dev = (unsigned int)strtoul(de->d_name + 12, NULL, 10);
>>>>>> +			break;
>>>>>> +		}
>>>>>> +	}
>>>>>> +	ret = errno;
>>>>>> +	if (ret)
>>>>>> +		pr_perror("Can't read dir\n");
>>>>>> +	else if (*s_dev)
>>>>>> +		pr_info("Found binfmt_misc img for dev=%u\n", *s_dev);
>>>>>> +	closedir(dir);
>>>>>> +
>>>>>> +	return ret ? -1 : (*s_dev != 0);
>>>>>> +}
>>>>>> +
>>>>>>  static int binfmt_misc_virtual(struct mount_info *pm)
>>>>>>  {
>>>>>>  	return kerndat_fs_virtualized(KERNDAT_FS_STAT_BINFMT_MISC, pm->s_dev);
>>>>>> @@ -2442,6 +2475,15 @@ static int do_new_mount(struct mount_info *mi)
>>>>>>  	if (tp->restore && tp->restore(mi))
>>>>>>  		return -1;
>>>>>>  
>>>>>> +	if (!mi->mnt_id) {
>>>>>> +		/* C-r time mountpoint, umount it */
>>>>>> +		if (umount(mi->mountpoint) < 0) {
>>>>>
>>>>> I don't see the corresponding mount() callback. Where is it?
>>>>
>>>> Generic code does this after mount_info is created in add_cr_time_mount().
>>>
>>> Ah! OK, we need a code comment saying this explicitly.
>>>
>>>>>> +			pr_perror("Can't umount %s\n", mi->mountpoint);
>>>>>> +			return -1;
>>>>>> +		}
>>>>>> +		goto out;
>>>>>> +	}
>>>>>> +
>>>>>>  	if (remount_ro && mount(NULL, mi->mountpoint, tp->name,
>>>>>>  				     MS_REMOUNT | MS_RDONLY, NULL)) {
>>>>>>  		pr_perror("Unable to apply mount options");
>>>>>> @@ -2461,7 +2503,7 @@ static int do_new_mount(struct mount_info *mi)
>>>>>>  	BUG_ON(mi->master_id);
>>>>>>  	if (restore_shared_options(mi, !mi->shared_id, mi->shared_id, 0))
>>>>>>  		return -1;
>>>>>> -
>>>>>> +out:
>>>>>>  	mi->mounted = true;
>>>>>>  
>>>>>>  	return 0;
>>>>>> @@ -3324,7 +3366,7 @@ static int populate_roots_yard(void)
>>>>>>  
>>>>>>  static int populate_mnt_ns(void)
>>>>>>  {
>>>>>> -	struct mount_info *pms;
>>>>>> +	struct mount_info *pms, *mi;
>>>>>>  	struct ns_id *nsid;
>>>>>>  	struct mount_info *roots_mp = NULL;
>>>>>>  	int ret;
>>>>>> @@ -3343,6 +3385,21 @@ static int populate_mnt_ns(void)
>>>>>>  	if (!pms)
>>>>>>  		return -1;
>>>>>>  
>>>>>> +	for (mi = mntinfo; mi != NULL; mi = mi->next) {
>>>>>> +		if (strcmp(mi->fstype->name, "binfmt_misc") == 0)
>>>>>> +			break;
>>>>>> +	}
>>>>>> +
>>>>>> +	if (!mi) {
>>>>>> +		unsigned int s_dev;
>>>>>> +
>>>>>> +		ret = find_binfmt_misc_img(&s_dev);
>>>>>> +		if (ret > 0)
>>>>>> +			ret = add_cr_time_mount(pms, "binfmt_misc", BINFMT_MISC_HOME, s_dev);
>>>>>> +		if (ret < 0)
>>>>>> +			return -1;
>>>>>> +	}
>>>>>> +
>>>>>>  	if (resolve_shared_mounts(mntinfo, pms->master_id))
>>>>>>  		return -1;
>>>>>>  
>>>>>>
>>>>>> _______________________________________________
>>>>>> CRIU mailing list
>>>>>> CRIU at openvz.org
>>>>>> https://lists.openvz.org/mailman/listinfo/criu
>>>>>> .
>>>>>>
>>>>>
>>>> .
>>>>
>>>
>> _______________________________________________
>> CRIU mailing list
>> CRIU at openvz.org
>> https://lists.openvz.org/mailman/listinfo/criu