[systemd-devel] Fwd: Does Systemd also mount sysfs, procfs?

[유준봉]

Hi I just started to understand systemd source code.

Now I'm curious about mounting linux pseudo-filesystemd like sysfs and
porcfs.

In main( ) function from /src/core/main.c, there is several mounting
related functions like:
1. mount_setup_early
2. mount_setup
3. mount_cgroupt_controllers
and also, there is table named 'mount_table'

I used log_info( ) to see which file systems that systemd mounts. But none
of them was sysfs or procfs(systemd only mounts: securityfs, tmpfs, devfs,
etc. but not sysfs and procfs).

I also tracked why systemd does not mount sysfs and procs.
Inside mount_one( ) function, systemd uses name_to_handle_at( ) to get
mount_id.

For sysfs('/sys'), or procfs('/proc'), name_to_handle_at( ) returns
fail(EOPNOTSUPP). But for its parent('/'), name_to_handle_at( ) returns
success. and in this case, systemd doesn't mount such file systems.

Now, this is my question:
What this situation means when child directory returns fail for
name_to_handle_at( ) but its parent returns success for the same function?
does it mean '/sys' is already mounted before '/sbin/init' is executed? If
so, then who mounts sysfs, procfs, and also rootfs?(script? other initial
process?)

I know it is very basic question for linux programmer, but please give me
some answer about this.
TIA.
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