On Wed, 2017-07-19 at 08:49 +0200, Milan Crha wrote:
On Tue, 2017-07-18 at 15:51 -0400, Matthew Miller wrote:
> * ability to mix and match versions and streams
Hi Milan -
Thanks for all the questions! Some of these are better brought up on a
Flatpak or GNOME mailing list and you'd get better answers, but I'll
answer to the best of my ability here.
I also think that Evolution is pretty much a worse case scenario for
putting into a Flatpak - it stores huge amounts of data, shares that
data with the rest of the GNOME desktop, and has all sorts of
complicated ties built up over many years of shared history. It's great
to think about how it will work in a Flatpak, but we shouldn't get
depressed if it seems hard - not all applications are that hard!
my personal knowledge of Flatpak is close to zero at the moment,
this is more a newbie reply.
My understanding of Flatpak, and the main advantage of it from my
point of view, is to get most recent versions of applications to the
users as soon as possible, without a need to reinstall whole system
due to (up or down) dependencies, which sounds pretty cool. One can
run software for the most recent Fedora on years old Fedoras (not
only Fedora, but let's make it simple here), everything is just a
matter of using proper runtime and bundle libraries which are
required for the application.
The downside is disk usage, but I do not want to reopen this here, it
had been widely discussed in the "F27 System Wide Change: Graphical
Applications as Flatpaks" thread. I suppose you plan to have several
runtimes, to avoid having installed Fedora, then two other Fedoras as
runtimes, when one would like to test two different versions on a
running system, where the same application (and/or its possibly
incorrect dependencies) is installed as well.
I'm not entirely sure I follow the question, but yes, if you want to
run F27 applications, you'd have the F27 runtime installed as well.
It's not going to be tiny, but it will be a lot smaller than a full
install of F27.
That thread opened also one question about versions and user data.
you use an application which changed its internal data format between
two versions, but you still want to run both versions (like to be
able to test differences and eventually catch regressions), then you
cannot share user data between them, can you? The application
certainly supports switch from old format to the new, not vice versa
(how would old software knew about the new format?). How is this
dealt with in Flatpak world? Should each application tell Flatpak to
use different XDG directories, in which case the user data will not
be shared between applications?
Well, it's largely up to the application author to evolve their data
and settings in a way that is backwards compatible. I think a lot of
application authors do that anyways, because they want to be working on
new versions of their application while still maintaining a stable
branch. If an application has to break storage formats, it probably is
better to do it as a one-time-migration leaving the old data in place.
(This is obviously not practical if the data is 20GB of email!)
Flatpak bases where it stores the data of the application off of the
application ID. You can change the application ID and get a clean slate
- but then you don't have migration. (Nightly development builds in
particular may use a different application ID so that they can be tried
What about DConf settings. While at least I only add new GSettings
keys, once some version removes a key it cannot be shared with the
older versions (GSettings aborts the application on missing
schemas/keys), or it'll be a mess, on the first look.
GSettings schemas are considered part of the application, and are
shipped in the Flatpak. What would be shared is the (schema-less) DConf
storage. If the DConf storage mismatches the schemas, the schemas will
be used to provide default values.
There are certainly still cases where the application could change
settings in a way that would cause old application versions to have
problems. Application authors generally need to to take care not to
change the meaning of existing settings keys, only add new ones.
What about critical path packages? Are those meant to be part of the
runtime? Or should each of the applications bundle them? Imagine a
real life example, gnome-todo, gnome-contacts, gnome-calendar and
Evolution. They all use evolution-data-server and it's evolution-
data-server,which takes care of storing locally cached data. The
3.26.x has changed background data storage for contacts and
calendars. If I want to be sure that each of them uses correct data
server, then either I bundle it to each of them, or I use a runtime
which contains it. Due to the data format change I cannot use shared
home, even though they all are meant to share it, to avoid
redefinition of the accounts for each application (passwords/OAuth2
tokens through keyring could be probably shared).
evolution-data-server is definitely a problem for the Flatpak model -
the entire idea of Flatpak is that different applications and the
operating system can be updated separately. If Evolution, GNOME
Contacts, and the operating system (GNOME Shell) are bound together by
a complicated, evolving D-Bus service, then that simply isn't possible.
It would be possible to have contacts and calendar events as "portals"
- as services provided by the operating system to applications. But
then that would have to be tightly version controlled, there would have
to be a security model, and there would have to be some plan that would
work when the desktop doesn't include EDS (what if you are running on
KDE?) Would the flatpak runtime include a simple implementation?
Generally, it's least surprising if data is scoped to the application,
and that's the model we plan for. But I understand it's not how
Evolution works currently. I'd encourage you to discuss this within the
What about the connection to GNOME Online Accounts? To have
consistent behavior, bundle it as well? Or it'll be part of some
runtime? Could those GOA accounts be shared between different
versions? There's similar problem with internal data format like with
the data server.
I don't think bundling GNOME Online Accounts makes sense - it appears
like part of the desktop to the user. In the unsandboxed case, you can
just access the D-Bus service from your application.
We'd need an "accounts portal" of some sort for the sandboxed case,
figuring out the security model and user interaction, since arbitrary
applications should definitely not be able to get your credentials from
GOA. Again you'd need a fallback implementation - which could simply be
"no I don't have any account information".
I've been told that debugging of Flatpak applications is no fun.
didn't try it myself, thus I cannot tell for sure, but for me as a
consumer the use of Flatpak to deliver software early also means that
I'd be able to debug regressions easily, from getting debug logs
turned on with environment variables, down to getting useful
backtraces of crashed or running applications.
We definitely don't want debugging Flatpak applications to be no fun!
Some of it is a matter of maturity of tooling, some of it is a matter
of experience... hopefully it's getting better all the time.
With Flatpaks built with flatpak-builder, the debug information is
available as an "extension" that you can install with the application.
The same will have to be done for Flatpaks built with Fedora content,
though we haven't fully figured out the details there.
That is, if I want to deliver an application to the users early, no
matter what distribution they use, I'm meant to use proper runtime,
bundle as much as possible, thus the code can actually run anywhere
and consistently, and use specific XDG directories per each Flatpak.
That pretty much sounds like a work for the upstream, not for the
Fedora, because using Fedora runtime means getting tight to Fedora
only. Or not? My natural choice would be to use GNOME runtime instead
(though I've no idea about its usability on other distributions than
it is built on).
It will be entirely possible to run Fedora Flatpaks on other
distributions - to say "if you want to try out Evolution 3.26 - install
the Fedora flatpak". A user that installs the Fedora flatpak will see
the Fedora stream of security updates - you'd need to be responsible
for that yourself if you shipped an application built directly from