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overlay.d/05core: support booting ISO completely from RAM #2544

Merged
merged 2 commits into from
Aug 14, 2023
Merged

overlay.d/05core: support booting ISO completely from RAM #2544

merged 2 commits into from
Aug 14, 2023

Commits on Aug 14, 2023

  1. overlay.d/05core: drop RHEL8 workarounds for live-generator 

    This should be dead code now.
    @dustymabe
    dustymabe committed Aug 14, 2023
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  2. overlay.d/05core: support booting ISO completely from RAM 

    It has been presented to us a use case where the user wants to actually
"install" directly to the same device that was used to boot the live
ISO image (i.e. the ISO was written to a block device and then booted
from). The way the ISO boots today it mounts the ISO at /run/media/iso
and then mounts the CoreOS rootfs from a file under that mountpoint. In
this scenario /run/media/iso will be busy and can't be unmounted because
the root filesystem of the live running system depends on it.

We can adjust the strategy slightly to get a system that runs completely
from memory (similar to live PXE systems) by just copying the file out
of /run/media/iso and into memory before doing the rootfs mount, which
will allow /run/media/iso to be unmounted before the installation
commences.

This patchset adds a new coreos.liveiso.fromram option to allow
requesting this new behavior. We could consider making this new
behavior the default, but we'd need to consider the new RAM requirements.
For example, before this change on a 2G FCOS system the usage after
booting looks like:

```
[core@localhost ~]$ free -m
               total        used        free      shared  buff/cache   available
Mem:            1953         163        1286         125         503        1519
Swap:              0           0           0
```

With this change (and the coreos.liveiso.fromram kernel arguemnt
specified) the usage looks like:

```
[core@localhost ~]$ free -m
               total        used        free      shared  buff/cache   available
Mem:            1953         173         688         808        1091         824
Swap:              0           0           0
```

The usage would scale with the size of the rootfs. i.e. RHCOS is larger
so the memory requirements would be larger too.
    @dustymabe
    dustymabe committed Aug 14, 2023
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