Re: [PATCH v3 01/22] host/rootfs: Mount filesystems before s6-rc-init

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 7/13/26 05:39, Alyssa Ross wrote:
> Demi Marie Obenour <demiobenour@gmail.com> writes:
> 
>> cgroup-setup is written in Rust and uses the Rust standard library.
>> It also relies on cgroupfs being mounted at /sys/fs/cgroup.
>> Furthermore, it runs very, *very* early on, since it sets up the cgroups
>> in which s6-svscan and s6-supervise processes run.  This allows setting
>> up sub-cgroups without having to worry about name collisions.
>>
>> While it would be possible to only mount the bare minimum necessary,
>> it's simpler to just mount everything before starting any services.
>> These mounts are all pseudo-filesystems or tmpfs instances, and none
>> have any dependencies.
>>
>> Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
>> ---
>>  host/rootfs/image/etc/init                          | 11 ++++++++++-
>>  host/rootfs/image/etc/s6-linux-init/scripts/rc.init |  9 +--------
>>  2 files changed, 11 insertions(+), 9 deletions(-)
>>
>> diff --git a/host/rootfs/image/etc/init b/host/rootfs/image/etc/init
>> index db8a6d9c747e3d212c21b6c983c8f7e299822abe..8ec7859ab00e24007a93d4000c8f34e353de50ae 100755
>> --- a/host/rootfs/image/etc/init
>> +++ b/host/rootfs/image/etc/init
>> @@ -1,6 +1,15 @@
>>  #!/bin/execlineb -Ws0
>>  # SPDX-License-Identifier: EUPL-1.2+
>> -# SPDX-FileCopyrightText: 2022 Alyssa Ross <hi@alyssa.is>
>> +# SPDX-FileCopyrightText: 2020-2022, 2024 Alyssa Ross <hi@alyssa.is>
>>  
>>  /bin/setpriv --no-new-privs --
>> +
>> +if { /bin/ln -s /proc/self/fd /dev }
>> +if { /bin/ln -s /proc/self/fd/0 /dev/stdin }
>> +if { /bin/ln -s /proc/self/fd/1 /dev/stdout }
>> +if { /bin/ln -s /proc/self/fd/2 /dev/stderr }
> 
> I guess the idea is that the Rust standard library might want these?

I don't know if it actually does, though I would not be surprised if
it is not tested without them.  What *is* necessary is for a cgroup
filesystem to be mounted at /sys/fs/cgroup.  This allows setting up
cgroup controllers and moving PID 1 to a sub-cgroup.

>> +
>> +if { /bin/mount --make-shared / }
>> +if { /bin/mount -a --mkdir }
>> +
>>  /bin/s6-linux-init -c /etc/s6-linux-init -s /run/param -- $@
>> diff --git a/host/rootfs/image/etc/s6-linux-init/scripts/rc.init b/host/rootfs/image/etc/s6-linux-init/scripts/rc.init
>> index f638e373589884acb959c868462fdf532380a851..fba305c4e9cbb9f7535f11bb4c06d8da8a34837b 100755
>> --- a/host/rootfs/image/etc/s6-linux-init/scripts/rc.init
>> +++ b/host/rootfs/image/etc/s6-linux-init/scripts/rc.init
>> @@ -4,13 +4,6 @@
>>  
>>  if { s6-rc-init -c /etc/s6-rc /run/service }
>>  
>> -if { ln -s /proc/self/fd /dev }
>> -if { ln -s /proc/self/fd/0 /dev/stdin }
>> -if { ln -s /proc/self/fd/1 /dev/stdout }
>> -if { ln -s /proc/self/fd/2 /dev/stderr }
>> -
>> -if { mount --make-shared / }
>> -if { mount --make-shared /run }
>> -if { mount -a --mkdir }
>> +if { /bin/mount --make-shared /run }
> 
> Presumably this does not actually suddenly need an absolute path.

You are correct.

>>  
>>  s6-rc change ok-all
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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