Re: [Zero-install-devel] 0install & unionfs

[David G. <dg...@co...>]

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Thomas Leonard wrote:
[...]
> I've recently added the <overlay> binding element to the spec to allow
> feeds to say that they need this:

Hurray!

[...]
> However, it's not yet implemented. We need to decide which of the many
> systems to use! This Klik2 wiki page has a summary of the options:
[...]
> Any thoughts?

The obvious thing to do is to make the runtime modular enough that you ca=
n
drop in any sane unionfs system and have it work.

In terms of actual technology, then if the host OS provides a real unionf=
s,
then that would be preferable; failing that, ptrace is probably the way t=
o go.
(ptrace is a bit slower than FUSE but easier to use and doesn't require r=
oot
privileges. See http://www.am-utils.org/project-goanna.html, but they hav=
en't
released any code yet; however, I've been in touch with the plasticfs guy=

who's definitely interested in changing his code from LD_PRELOAD to ptrac=
e.)

LD_PRELOAD should not be used for anything, IMO --- because it operates a=
t a
library level rather than a syscall level it doesn't work on programs tha=
t
make syscalls directly --- such as any static binary. This means that
fakechroot needs to be considered advisory only, and has no meaningful
security aspects. (Also, the glibc people are planning on deprecating LD_=
PRELOAD.)

- --
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