old version image /etc/mtab problem

[liuchangyan]

In our production environment, we just switch containerd runtime fromdocker to containerd, we ran into a problem: there is a container running base on a super old version image which has a physical document /etc/mtab, it‘s content is :

sh-4.1# ls -l /etc/mtab
-rw-r--r--. 1 root root 129 Aug 20  2015 /etc/mtab

sh-4.1# cat /etc/mtab
/dev/sda1 / ext4 rw 0 0
devpts /dev/pts devpts rw 0 0
tmpfs /dev/shm tmpfs rw 0 0
proc /proc proc rw 0 0
sysfs /sys sysfs rw 0 0

and the mount and df -h command has no expect results which shound have overlay mount messages:

sh-4.1# mount
/dev/sda1 on / type ext4 (rw)
devpts on /dev/pts type devpts (rw)
tmpfs on /dev/shm type tmpfs (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)

sh-4.1# df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        70G   29G   42G  41% /
tmpfs            64M     0   64M   0% /dev/shm

but in normal image, after mounting rootfs，the /etc/mtab should be a softlink to /proc/mounts, and mount command will read /etc/mtab by default:

sh-4.2# ls -l /etc/mtab
lrwxrwxrwx. 1 root root 17 Jul  2  2016 /etc/mtab -> /proc/self/mounts

sh-4.2# df -h
Filesystem      Size  Used Avail Use% Mounted on
overlay          70G   30G   41G  43% /
tmpfs            64M  4.0K   64M   1% /dev
shm              64M     0   64M   0% /dev/shm
tmpfs            64M   12K   64M   1% /run
tmpfs            30G     0   30G   0% /proc/acpi
tmpfs            30G     0   30G   0% /proc/asound
tmpfs            30G     0   30G   0% /sys/firmware
tmpfs            30G     0   30G   0% /proc/scsi

sh-4.2# mount
overlay on / type overlay (rw,relatime,seclabel,lowerdir=/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/63/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/62/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/61/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/60/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/59/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/58/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/57/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/56/fs:/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/55/fs,upperdir=/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/145/fs,workdir=/var/lib/containerd/io.containerd.snapshotter.v1.overlayfs/snapshots/145/work)
proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
tmpfs on /dev type tmpfs (rw,nosuid,seclabel,size=65536k,mode=755)
devpts on /dev/pts type devpts (rw,nosuid,noexec,relatime,seclabel,gid=5,mode=620,ptmxmode=666)
shm on /dev/shm type tmpfs (rw,nosuid,nodev,noexec,relatime,seclabel,size=65536k)
mqueue on /dev/mqueue type mqueue (rw,nosuid,nodev,noexec,relatime,seclabel)
sysfs on /sys type sysfs (ro,nosuid,nodev,noexec,relatime,seclabel)
tmpfs on /run type tmpfs (rw,nosuid,seclabel,size=65536k,mode=755)
proc on /proc/bus type proc (ro,nosuid,nodev,noexec,relatime)
proc on /proc/fs type proc (ro,nosuid,nodev,noexec,relatime)
proc on /proc/irq type proc (ro,nosuid,nodev,noexec,relatime)
proc on /proc/sys type proc (ro,nosuid,nodev,noexec,relatime)
proc on /proc/sysrq-trigger type proc (ro,nosuid,nodev,noexec,relatime)
tmpfs on /proc/acpi type tmpfs (ro,relatime,seclabel)
tmpfs on /proc/asound type tmpfs (ro,relatime,seclabel)
tmpfs on /proc/kcore type tmpfs (rw,nosuid,seclabel,size=65536k,mode=755)
tmpfs on /proc/keys type tmpfs (rw,nosuid,seclabel,size=65536k,mode=755)
tmpfs on /proc/timer_list type tmpfs (rw,nosuid,seclabel,size=65536k,mode=755)
tmpfs on /proc/sched_debug type tmpfs (rw,nosuid,seclabel,size=65536k,mode=755)
tmpfs on /sys/firmware type tmpfs (ro,relatime,seclabel)
tmpfs on /proc/scsi type tmpfs (ro,relatime,seclabel)

this problem is much more like this issue containerd/containerd#2419, and we all know there is inappropriate to add this logic in containerd, but it is harder to push others to rebuild the image，so we made a small patch on this issue: https://github.com/opencontainers/runc/compare/main...liuchangyan:runc:main?expand=1, just a draft code.
We would like to know if our solution feasible or not, and is there some kind advice for us to resolve this problems? Looking forward to your reply~