David Planella <david.plane...@ubuntu.com> wrote:
>Al 05/09/12 05:18, En/na Emmet Hikory ha escrit:
>> Steve Langasek wrote:
>>> On Tue, Sep 04, 2012 at 05:20:47PM -0400, Michael Hall wrote:
>>>>> It's possible that namespacing within /usr - for instance,
>>>>> requiring each subdirectory and binary name to be prefixed with
>>>>> 'extras.' - would give better results with regards to the upstream
>>>>> build systems, I'm not sure. But if we are going to try to do
>>>>> namespacing of extras packages to avoid the need for coordination,
>>>>> we definitely would need improved package helpers that support
>>>>> namespacing of packages (i.e., debhelper support).
>>>
>>>> Would it be reasonable for MyApps to add a package name prefix to
>the
>>>> submitted package, rather than requiring the developer to do so?
>>>> MyApps will already be modifying the submitted package to include
>the
>>>> generator AppArmor profile.
>>>
>>>> So, for example, if I submit quickly-gtk as a source package to
>>>> MyApps, it would convert it to extras-quickly-gtk, add the AppArmor
>>>> profile, and re-build the source package before submitting it to
>the
>>>> PPA/buildds.
>>>
>>> For package renaming that seems easy enough to do, but if we're
>worried
>>> about file conflicts, dynamically prefixing filenames when building
>the
>>> package is going to have an even worse impact on the upstream code
>than
>>> changing directories does.
>>
>> Changing the base filename indeed generates more complicated
>issues,
>> not only in terms of collisions, but also in terms of coordination
>between
>> code and data (e.g. code expects to find ${CONFIG_DIR}/package and
>fails
>> to initialise properly with only ${CONFIG_DIR}/extras-package.
>>
>> However, if we consider "renaming" to apply to the entire path,
>rather
>> than the bare filename, this becomes considerably less of an issue.
>If
>> MyApps were to call tooling that changed the default installation
>location
>> for files while preserving bare filenames, then there is less
>potential
>> for conflict. The standard mechanism for this is to place the
>non-system
>> files in per-package namespaced directories in /opt.
>>
>
>I fully sympathize and understand the advocacy for the use of /opt at
>the packaging level and I would in principle support it: it is the
>standard FHS location for add-on software packages and it creates a
>separate installation namespace that prevents file collisions. In
>theory, it seems the best approach.
>
>However, reality has shown that (a) it is a big hurdle for app
>developers (who are actually the people we're trying to make the
>process
>easier for) to follow this policy and (b) we're enforcing a policy not
>even our tools support.
>
>For (b), what I believe is that it is also clear that no one is going
>to
>work to improve /opt support in tooling or in developer toolkits in the
>near or distant future. So for this alone I consider it to be a dead
>end.
>
>We are assuming that build systems and libraries are flexible enough to
>cater for an alternative installation prefix, and that it will all just
>work at runtime. Unfortunately, this has proven not to be the case. And
>I think the amount of coordination and work that'd be required to
>provide solid /opt support in Ubuntu would be best put in other parts
>of
>the spec, such as its central one: sandboxing.
>
>Just to illustrate the kind of issues we've bumped into in MyApps
>submissions, here's just an example [1]: GtkBuilder does not work with
>the gettext Python library if you specify an alternative location to
>load translations from (e.g.
>'/opt/extras.ubuntu.com/$APP/share/locale/'). So we had to either wait
>or contribute to fix the upstream bug (unlikely as per the complexity
>involved) or implement a workaround. The workaround was to get Quickly
>to modify the source code to use 'locale' instead of 'gettext': an
>effective but nasty solution.
>
>And that's been the journey with /opt so far: continually playing catch
>with the next exception we have to fix or work around. This does not
>sound like a very solid approach or a good experience to provide to app
>developers. And again, I think we should rather direct resources where
>higher priorities lie.
>
>While I like Emmet's idea of delegating the changes required to work
>with /opt to MyApps, this would also mean that the complexity in the
>logic behind the server would greatly increase. And in some cases (e.g.
>hardcoded paths) we would also need to actually modify the sources to
>ensure an app runs.
I understand it would be a lot of work and people aren't working on it. What's
your basis for believing there will be resources available to implement this
alternate approach?
>Summarizing, I think these are the 3 main points of discussion right
>now:
>
>* Package name conflicts: it seems that we've agreed that a solution
>for
>package name conflicts is to rely on 'extras-' prefixing on the server
>side (i.e. MyApps). This seems to be easy enough to do, fit well with
>other parts of the spec and would be transparent to app developers.
Agreed.
>* File name conflicts: there I would suggest exploring Daniel's
>proposal
>of relying on a conflict checker that works across all archives, so
>that
>before an upload is accepted this service checks for any potential
>clashes and informs the uploader to fix the package before they can do
>the next submission. The uploader would either be an Ubuntu developer
>(through the main archive) or an app developer (through extras, via
>MyApps). This would not only benefit the app developer process, but
>also
>fix the existing issue in the regular Ubuntu upload process.
This would be useful, but insufficient.
>* Namespace ownership: even with conflict checking there is the issue
>of
>who gets to own a particular file name or namespace. E.g. would "Mad
>Feathered Creatures" (/usr/bin/birds, from Extras) have priority in
>owning the binary's name if it had been submitted before "Jolly Flying
>Animals" (also /usr/bin/birds, from Universe)? I think if we want to
>make apps first-class citizens, even if not part of the distro, a
>simple
>suggestion would just be to do it on a first-come-first-serve basis.
I think it is fundamentally incorrect to give something built on Ubuntu
namespace priority over Ubuntu itself. Additionally, if this service proves
popular, this approach would drive a permanent namespace wedge between Debian
and Ubuntu that might, over time, significanly change the nature of the
relationship between the two distributions.
>What are your thoughts on these?
>
>Finally, I believe we do need to provision for those cases, but my
>understanding is that the potential amount of occurrences would be
>rather low. So do you think they justify additional Engineering work,
>or
>rather they could be dealt manually on a case-by-case basis?
>
You've got to consider it now or it won't scale. IIRC the original
presentations on this topic at UDS Orlando(?), the intent was to be able to
scale out to hit numbers of applications equal to or greater than the Apple
Appstore/Google Play. If you hit that, then MyApps ends up being several times
the size of the Ubuntu archive.
At that scale I doubt it's feasible to keep file name uniqueness even among
MyApps packages. If you want to scale there will have to be some kind of
separation in the file namespace. Using /opt was an attempt at this. BSD Unix
separates system and applications by putting applications in /usr/local. That
kind of approach doesn't really help here.
Based on the discussion in this thread, I'm now convinced that an environment
where MyApps packages live in their own namespace is absolutely essential to a
scalable process. I'm also almost as convinced that a file system based
separation won't be achieved.
Fundamentally, I think any successful solution is going to have to place each
package in its own containerized namespace. Anything else is going to collapse
under its own weight if it's successful.
I think it's better to head down this road now (even if it's harder to do) than
to take the proposed approach and then have to through it out in a year or two
and go down the container route anyway.
Scott K
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