Re: Sandboxed Gnome apps

On Thu, 2014-09-04 at 19:05 +0200, Alexander Larsson wrote:
I guess by now most people have seen lennarts latest post on how to
build linux systems:

So, what does Gnome need to provide here?

1. A platform definition
2. A reference implementation
3. A SDK and other tooling
For 1), 2) and 3), and at the risk of causing a flamewar, couldn't we
rely on packages from a distribution to bundle those?

I could imagine rather trivially creating images from Fedora for
example, so that the GNOME project doesn't have to take care of tracking
NSS, glibc or Mesa (as you mentioned later).

Whichever platform we end up building from, we probably don't want to do
the building of those parts ourselves, with all the security,
trackability and reproducibility that we would need to implement to take
care of this.

4. IPC stability guarantees

   In theory we can put any kind of library in the runtime, as we rely
   on the global version of the runtime itself to keep applications
   running if API or ABI change. (Although we should of course try to
   minimize such breaks.) However, any kind of IPC mechanism we include
   in the runtime must have very strict backwards compatible

   Historically we have not done very well here. For instance, the GVfs
   dbus interfaces have generally been tightly coupled with the client
   libraries, such that you have to update both in lockstep. With an
   "app" based setup we have to take backwards compatibility much more  
   seriously, across the board. 

   This is not a code delivery, but rather a change in mentality that
   we as a project have to accept.

I don't understand the problem with gvfs. gvfs would be at the same
level as GIO or glib, and the clients would only see the public GIO API,
nothing outside it.

I've recently started looking at how 1-3 could be done. I've
experimented with openembedded which is a very nice way to do cross
compilation that also lets you create SDK. However, some of stuff, in
particular gobject-introspection is very tricky to do right when cross
compiling. I've now changed over to the mixed model that
gnome-continuos is using where openembedded is used to build a base
containing the build environment, and the rest is built in a chroot.

Why do we care about cross-compiling? For all the platforms we might
want to target (that's the 32-bit and 64-bit variants of x86 and ARM),
there are already machines that are fast enough to build natively.
That's what Fedora does, and that's probably good enough.

Hopefully I will have some initial cut of a runtime based on
gnome-continuos some time next week. This will give us a runtime, but
also a lot of stuff that can be used to make the SDK.

This will give us a runtime that's not easily reproducible or trackable.

We need to start looking into exactly what the runtime should include
though. Obviously it should contain glib, gtk+ and the gnome platform,
but we also need to pick the lower level dependencies (glibc, X, etc)
as well as some level of standard unix tools.

For instance:
 * Do we ship a shell interpreter so that shell scripts work?
 * What standard unix tools do we ship? cp? ps? ship? awk? sed?
 * What about language runtimes? gjs? pyton2? python3? perl5?
 * Some of our development stack is of lower quality than the core
   platform. How much of it do we want to ship? On one hand we
   can put whatever in the runtime and have the runtime versioning
   protect against stability issues, on the other hand we'll may be
   giving application developers false hope wrt the quality and
   stability of some code, as well as setting us up for long-term
   maintainance and security fixes for all those libraries.
 * What about things like plugins like gstreamer? We'll ship some 
   in the runtime, and if the app needs a particular new one it can
   bundle it. But it would also be nice if the user can side-load
   things into a specific runtime. Maybe we need extra local layers on
   top of the runtime?

There are also lots of technical issues. For instance how do we ship
mesa and DRI drivers which have dependencies on the kernel part of the
driver? How do we support e.g. the nvidia drivers in this? Do we need
some kind of overlay for the runtime image for local hardware drivers?

That's also something I mentioned to Lennart and David Airlie. I don't
think there are that many interdependencies between the kernel and Mesa
when it comes to normal usage, but the runtime providers updating Mesa
will be a requirement to having new hardware supported.

Well, this was a lot of text from my side with nothing practicaly
useful yet. I think its good to get people started thinking about these
things though, and I'll keep people updated as I make progress actually
building something.

My advice is, as for the test ISO images where we scrub Fedora branding
out of the images, to use an established distro to base our reference
image and SDK. I don't particularly mind if it's Fedora, Debian or
something else, those who do the work will get to choose :)


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