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

[Kirill Tkhai]

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?

> 
>> +		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().
 
>> +			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;
>>  
>>
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>> .
>>
>