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

[Andrew Vagin]

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

> 
> > 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) &&
> >>>
> >>
> > .
> > 
>