[gentoo-user] Docker and filesystem mounts

[D. Ben Knoble]

Hi folks, question for you about Docker on Linux:

Anybody know why /var/lib/docker appears to be a 2nd mountpoint of the
partition that has my root filesystem on it? Searching says something
about "loopbacks" but I don't have /dev/loop*, so I'm not sure how to
interrogate more about what's going on here (and searching the
internet is tough because I'm not sure what question to ask).

    # lsblk
    NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
    nvme1n1     259:0    0  1,8T  0 disk
    nvme0n1     259:1    0  1,8T  0 disk
    ├─nvme0n1p1 259:2    0    1G  0 part /efi
    ├─nvme0n1p2 259:3    0   30G  0 part [SWAP]
    └─nvme0n1p3 259:4    0  1,8T  0 part /var/lib/docker
                                         /
    # findmnt | grep p3
    /                             /dev/nvme0n1p3                  xfs
       rw,noatime,inode64,logbufs=8,logbsize=32k,noquota
    └─/var/lib/docker             /dev/nvme0n1p3[/var/lib/docker] xfs
       rw,noatime,inode64,logbufs=8,logbsize=32k,noquota

I did see the udev rule about hiding loopback devices from udisks:

    # hide docker's loopback devices from udisks, and thus from user desktops
    SUBSYSTEM=="block", ENV{DM_NAME}=="docker-*",
ENV{UDISKS_PRESENTATION_HIDE}="1", ENV{UDISKS_IGNORE}="1"
    SUBSYSTEM=="block", DEVPATH=="/devices/virtual/block/loop*",
ATTR{loop/backing_file}=="/var/lib/docker/*",
ENV{UDISKS_PRESENTATION_HIDE}="1", ENV{UDISKS_IGNORE}="1"

but I don't know where to look for that "loop" devpath (I don't see it
in /sys or /dev).

I'm considering trying out Podman instead, but I came across this and
got curious ;)

-- 
D. Ben Knoble