[CRIU] Sync TODO-s for mount.c work

[Oleg Nesterov]

On 04/22, Tycho Andersen wrote:
>
> On Wed, Apr 22, 2015 at 06:48:17PM +0200, Oleg Nesterov wrote:
> >
> > Let me start from the very beginning.
> >
> > 	# unshare -m
> > 	# perl -e 'close STDIN; close STDOUT; close STDERR; sleep'
> >
> > dump/restore from the root ns works.
> >
> > 	# unshare -m
> > 	# mount --make-slave /
> > 	# mount --make-shared /
> > 	# perl -e 'close STDIN; close STDOUT; close STDERR; sleep'
> >
> > dump/restore still work
>
> I'm confused about why this works, it seems like you have external
> masters in this case too. Can you post the mountinfo?

	# cat /proc/self/mountinfo
	17 38 0:3 / /proc rw,nosuid,nodev,noexec,relatime shared:5 - proc proc rw
	18 38 0:16 / /sys rw,nosuid,nodev,noexec,relatime shared:6 - sysfs sysfs rw,seclabel
	19 38 0:5 / /dev rw,nosuid shared:2 - devtmpfs devtmpfs rw,seclabel,size=16374292k,nr_inodes=4093573,mode=755
	21 19 0:17 / /dev/shm rw,nosuid,nodev shared:3 - tmpfs tmpfs rw,seclabel
	22 19 0:11 / /dev/pts rw,nosuid,noexec,relatime shared:4 - devpts devpts rw,seclabel,gid=5,mode=620,ptmxmode=000
	23 38 0:18 / /run rw,nosuid,nodev shared:22 - tmpfs tmpfs rw,seclabel,mode=755
	24 18 0:19 / /sys/fs/cgroup rw,nosuid,nodev,noexec shared:8 - tmpfs tmpfs rw,seclabel,mode=755
	25 24 0:20 / /sys/fs/cgroup/systemd rw,nosuid,nodev,noexec,relatime shared:9 - cgroup cgroup rw,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd
	38 1 253:1 / / rw,relatime shared:1 - xfs /dev/mapper/rhel_ibm--x3650m4--02--vm--02-root rw,seclabel,attr2,inode64,noquota
	#
	# unshare -m
	# mount --make-slave /
	# mount --make-shared /
	#
	# cat /proc/self/mountinfo
	26 20 253:1 / / rw,relatime shared:7 master:1 - xfs /dev/mapper/rhel_ibm--x3650m4--02--vm--02-root rw,seclabel,attr2,inode64,noquota
	27 26 0:5 / /dev rw,nosuid shared:2 - devtmpfs devtmpfs rw,seclabel,size=16374292k,nr_inodes=4093573,mode=755
	28 27 0:17 / /dev/shm rw,nosuid,nodev shared:3 - tmpfs tmpfs rw,seclabel
	29 27 0:11 / /dev/pts rw,nosuid,noexec,relatime shared:4 - devpts devpts rw,seclabel,gid=5,mode=620,ptmxmode=000
	30 26 0:3 / /proc rw,nosuid,nodev,noexec,relatime shared:5 - proc proc rw
	31 26 0:16 / /sys rw,nosuid,nodev,noexec,relatime shared:6 - sysfs sysfs rw,seclabel
	32 31 0:19 / /sys/fs/cgroup rw,nosuid,nodev,noexec shared:8 - tmpfs tmpfs rw,seclabel,mode=755
	33 32 0:20 / /sys/fs/cgroup/systemd rw,nosuid,nodev,noexec,relatime shared:9 - cgroup cgroup rw,xattr,release_agent=/usr/lib/systemd/systemd-cgroups-agent,name=systemd
	34 26 0:18 / /run rw,nosuid,nodev shared:22 - tmpfs tmpfs rw,seclabel,mode=755
	#
	# perl -e 'close STDIN; close STDOUT; close STDERR; sleep'

dump/restore works.


> When I do it I
> get:
>
> 152 151 253:1 / / rw,relatime shared:31 master:1 - ext4 /dev/disk/by-uuid/6c5a78e0-95fa-49a8-aa91-a8093d295e58 rw,data=ordered
>
> where the peer group 1 is the rootfs mount on root namespace.

Yes, same here. master==1.

> > 	# unshare -m
> > 	# mount --make-slave /
> > 	# mount --make-shared /
> > 	# mkdir /tmp/A /tmp/B
> > 	# mount --bind /tmp/A /tmp/B
> > 	# perl -e 'close STDIN; close STDOUT; close STDERR; sleep'
> >
> > Now it fails with the same
> >
> > 	Mount 35 ./tmp/B (master_id: 1 shared_id: 7) has unreachable sharing.
> >
> > error message.
> >
> > Why "restore" can't dump it? "restore" could simply do MS_BIND?
>
> Sorry, I'm not sure what you mean by "restore" here?

Argh. Sorry, I meant "why criu can't dump...".

> Anyway, yes, it
> could do MS_BIND with some sharing flags, I think we just haven't
> implemented that yet (this isn't an external mount, since it's bound
> within the namespace).

_Yes_ thanks. So can't we teach "auto" to do this?

OK, OK, perhaps we should not abuse --ext-mount-map option for that,
but this is minor.

Oleg.