disk space management

[Alexander Larsson]

On fre, 2016-06-17 at 18:54 -0700, Robert McQueen wrote:
> Hi there,
> 
> Two questions:
>   - where the base OS is managed by ostree, in the case that /var and
> / 
> are on the same filesystem, has anybody thought about any possible
> ways 
> to have the runtimes share the same checkout/repo that is used for 
> /ostree? Endless builds our runtimes and OS through the same binary 
> build system and makes ostrees as a separate phase, so it's
> reasonable 
> to assume a lot of binary identical file overlap between the OS and
> the 
> runtimes. it would be good to have those hardlinked together.

Flatpak does use some custom file locking to protect concurrent things,
so I can't offhand guarantee that is no issue with this, but I believe
it should be safe to just configure your /var/lib/flatpak/repo to point
to a shared ostree repo, as long as its on the same filesystem. The
branchnames used by flatpak are kinda special and will unlikely
conflict with the host image ones. Its possible that some code in
flatpak will currenly barf on unexpected branchnames, but that could
easily be fixed.

Actually, there might be an issue. Flatpak currently uses a "bare-user" 
mode repo, even for the system repo, while I believe ostree uses a
"bare" one. The difference is that a bare-user one can be checked out
in "user" mode using hardlinks, and a "bare" one can be checked out
with hardlinks in non-user mode. At one point the system flatpak repo
was a "bare" format, so it can certainly work like that, but "bare"
repos store permissions "as-is", which means that pulling e.g. a setuid
binary will store a setuid binary object in the repo. This isn't great
unless you fully trust the remotes you use and is the reason i moved to
a bare-user repo.

>   - on a similar vein, is it currently supported to run apps which
> are 
> installed in the user home directory if the runtimes are installed 
> system-wide?

Totally!

-- 
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 Alexander Larsson                                            Red Hat, Inc 
       alexl at redhat.com            alexander.larsson at gmail.com 
He's a shy albino cyborg on his last day in the job. She's a hard-bitten 
antique-collecting research scientist in the witness protection program. 
They fight crime!