[systemd-devel] [PATCH] readahead: add option to create pack in directory other than root

[Chaiken, Alison]

Lennart suggest:
>I am actually all for moving the file, though. But can't we find a more
>automatic solution for this, that doesn't
>require manual configuration. Maybe a scheme like this could work:
>a) readahead-reply would look for both /.readahead and
>   /var/lib/systemd/readahead. If both files exist, it picks the newer
 >  one, if only one exists it picks that one.

Upon further consideration, do we want a SUID program that is active at early boot to *automatically* prefer a newer file on a writable partition to an older one on a read-only partition?

Another aspect worth further consideration is, what is a graceful fallback strategy if for some reason the pack file gets corrupted?   Might it prevent a board with systemd-readahead-replay enabled from coming all the way up?   Has anyone ever observed a hang due to a corrupt pack?   When a watchdog reboots a hung board, perhaps we want to use a dynamic mechanism to point the pack file to /dev/null if we don't come up far enough to run "systemctl disable systemd-readahead-replay"?

Big props to the developers of systemd-readahead for the fact that such hangs due to corrupt pack files are obviously infrequent even when a developer tries inadvisable experiments with the code.

-- Alison