[CRIU] [PATCH 3/4] mount: add support for external block devices (v3)

[Pavel Emelyanov]

On 04/22/2016 08:23 PM, Andrew Vagin wrote:
> On Fri, Apr 22, 2016 at 07:01:22PM +0300, Pavel Emelyanov wrote:
>> On 04/22/2016 06:48 PM, Andrew Vagin wrote:
>>> On Fri, Apr 22, 2016 at 04:49:48PM +0300, Pavel Emelyanov wrote:
>>>> On 04/22/2016 09:12 AM, Andrey Vagin wrote:
>>>>> From: Andrew Vagin <avagin at virtuozzo.com>
>>>>>
>>>>> The idea is to allow to dump and restore mounts of
>>>>> a specified block device.
>>>>>
>>>>> Options:
>>>>> dump:		--ext-mount-map dev[MAJOR:MINOR]:VAL
>>>>
>>>> Why dev[MAJOR:MINOR]? Isn't just path (which is a mountpoint) enough?
>>>
>>> We don't know where this device is mounted, we know that this device
>>> may be mounted somewhere in a container.
>>
>> OK, then this is not the case for --ext-mount-map option :(
>> Let's step back a little. Which error do we hit when dumping this mount option?
> 
> [root at fc22-vm ~]# cat /proc/25743/mountinfo 
> 152 117 252:2 /root/git/criu/test / rw,relatime - ext4 /dev/vda2 rw,data=ordered
> 153 152 0:46 / /proc rw,nosuid,nodev,noexec,relatime - proc proc rw
> 118 152 0:47 / /dev/pts rw,relatime - devpts pts rw,mode=666,ptmxmode=666
> 119 152 7:1 / /zdtm/static/mnt_ext_dev.test rw,relatime - ext4 /dev/loop1 rw,data=ordered
> 120 119 7:1 /test_dir /zdtm/static/mnt_ext_dev.test/test_dir2 rw,relatime - ext4 /dev/loop1 rw,data=ordered
> 
> 
> (00.004858) Error (mount.c:731): mnt: FS mnt ./zdtm/static/mnt_ext_dev.test dev 0x700001 root / unsupported id 119

OK. Since v1.8 we can make --ext-mount-map work on fsroot mounts. If without applying your patch you
say --ext-mount-map /zdtm/static/mnt_ext_dev.test:ABC, will this unblock the dump?

>>
>>> In OpenVZ we can grant permissions to mount a block device in a
>>> container. And a user of CT decides where to mount this device.
>>>
>>>>
>>>>> restore:	--ext-mount-map VAL:DEVPATH
>>>>>
>>>>> If we find a mount with a specified block device, we
>>>>> set its type into FSTYPE__AUTO and write VAL into
>>>>> the "source" field.
>>>>>
>>>>> VAL is replaced on DEVPATH on restore.
>>>>>
>>>>> https://jira.sw.ru/browse/PSBM-39381
>>>>>
>>>>> v2: use --ext-mount-map instead of --external on dump
>>>>> v3: clean up
>>>>>
>>>>> Signed-off-by: Andrew Vagin <avagin at virtuozzo.com>
>>>>> ---
>>>>>  Documentation/criu.txt |  6 +++---
>>>>>  criu/mount.c           | 35 +++++++++++++++++++++++++++++------
>>>>>  2 files changed, 32 insertions(+), 9 deletions(-)
>>>>>
>>>>> diff --git a/Documentation/criu.txt b/Documentation/criu.txt
>>>>> index 1982f5d..07da757 100644
>>>>> --- a/Documentation/criu.txt
>>>>> +++ b/Documentation/criu.txt
>>>>> @@ -176,9 +176,9 @@ In other words, do not use it until really needed.
>>>>>      where locks are not holed by someone outside of it.
>>>>>  
>>>>>  *-M*, *--ext-mount-map* '<KEY>'*:*'<VAL>'::
>>>>> -    Setup mapping for external mounts. '<KEY>' is a mountpoint inside container
>>>>> -    and corresponding '<VAL>' is a string that will be written into the image
>>>>> -    as mountpoint\'s root value.
>>>>> +    Setup mapping for external mounts. '<KEY>' is a mountpoint or a device
>>>>> +    (dev[maj:min]]) inside container and corresponding '<VAL>' is a string
>>>>> +    that will be written into the image as mountpoint\'s root or source value.
>>>>>  
>>>>>  *--link-remap*::
>>>>>      Allow one to link unlinked files back when possible (modifies FS till *restore*).
>>>>> diff --git a/criu/mount.c b/criu/mount.c
>>>>> index f57b10c..f8d0cc2 100644
>>>>> --- a/criu/mount.c
>>>>> +++ b/criu/mount.c
>>>>> @@ -40,6 +40,8 @@
>>>>>  #undef	LOG_PREFIX
>>>>>  #define LOG_PREFIX "mnt: "
>>>>>  
>>>>> +static struct fstype fstypes[];
>>>>> +
>>>>>  int ext_mount_add(char *key, char *val)
>>>>>  {
>>>>>  	struct ext_mount *em;
>>>>> @@ -487,15 +489,31 @@ static void mnt_tree_show(struct mount_info *tree, int off)
>>>>>  static int try_resolve_ext_mount(struct mount_info *info)
>>>>>  {
>>>>>  	struct ext_mount *em;
>>>>> +	char devstr[64];
>>>>>  
>>>>>  	em = ext_mount_lookup(info->mountpoint + 1 /* trim the . */);
>>>>> -	if (em == NULL)
>>>>> -		return -ENOTSUP;
>>>>> +	if (em) {
>>>>> +		pr_info("Found %s mapping for %s mountpoint\n",
>>>>> +				em->val, info->mountpoint);
>>>>> +		info->external = em;
>>>>> +		return 0;
>>>>> +	}
>>>>>  
>>>>> -	pr_info("Found %s mapping for %s mountpoint\n",
>>>>> -			em->val, info->mountpoint);
>>>>> -	info->external = em;
>>>>> -	return 0;
>>>>> +	snprintf(devstr, sizeof(devstr), "dev[%d/%d]",
>>>>> +			kdev_major(info->s_dev),  kdev_minor(info->s_dev));
>>>>> +
>>>>> +	if (info->fstype->code == FSTYPE__UNSUPPORTED) {
>>>>> +		em = ext_mount_lookup(devstr);
>>>>> +		if (em) {
>>>>> +			info->fstype = &fstypes[1];
>>>>> +			BUG_ON(info->fstype->code != FSTYPE__AUTO);
>>>>> +			xfree(info->source);
>>>>> +			info->source = xstrdup(em->val);
>>>>> +			return 0;
>>>>> +		}
>>>>> +	}
>>>>> +
>>>>> +	return -ENOTSUP;
>>>>>  }
>>>>>  
>>>>>  static struct mount_info *find_widest_shared(struct mount_info *m)
>>>>> @@ -2091,6 +2109,11 @@ static char *resolve_source(struct mount_info *mi)
>>>>>  
>>>>>  	if (mi->fstype->code == FSTYPE__AUTO) {
>>>>>  		struct stat st;
>>>>> +		struct ext_mount *key;
>>>>> +
>>>>> +		key = ext_mount_lookup(mi->source);
>>>>> +		if (key)
>>>>> +			return key->val;
>>>>>  
>>>>>  		if (!stat(mi->source, &st) && S_ISBLK(st.st_mode) &&
>>>>>  		    major(st.st_rdev) == kdev_major(mi->s_dev) &&
>>>>>
>>>>
>>> .
>>>
>>
> .
>