On 06. 07. 21 20:38, David Cantrell wrote:
On Tue, Jul 06, 2021 at 01:20:47PM -0400, Ben Cotton wrote:
https://fedoraproject.org/wiki/Changes/tzdata-minimal
== Summary ==
Split the tzdata package into two parts - tzdata and tzdata-minimal.
tzdata will require tzdata-minimal. tzdata-minimal provides the
minimal files needed to support UTC on containers.
== Owner ==
* Name: Patsy Griffin (Franklin)
* Email: pa...@redhat.com
== Detailed Description ==
This is the first step towards providing support for a minimal, UTC
only, version of tzdata for containers. The tzdata-minimal package
will be a stand-alone, UTC only, subset of tzdata. The tzdata package
will require tzdata-minimal.
With this framework in place, other packages can develop code to
detect a minimal tzdata installation. These packages will also need
to provide appropriate messages when users request timezone
information not available when only tzdata-minimal is installed.
== Feedback ==
We have had requests for this functionality in order to support
minimal container installations. Currently some container kickstart
installations already ad hoc remove most of the timezone information
provided by tzdata, leaving only UTC support available. This change
provides a formal method of providing this support.
Both the glibc and python teams are aware of this proposed change.
This change does not currently require changes in their code. The
goal is for those packages that currently require tzdata as part of
their build or install, move towards recommending tzdata instead.
Python should work well without *any* tzdata installed.
But having only a small subset of timezones would result in issues
unique to Fedora-based systems (assuming those are the only systems that
split tzdata).
We could theoretically patch Python to give reasonable error messages.
But since the consumer of the tz data (the zoneinfo module) was only
added in Python 3.9 (last year), existing applications mainly use
third-party modules instead of the standard library. I assume that like
Python, these modules expect tzinfo to either be missing entirely or be
all there.
And I expect this is the case for more than just Python modules.
Is it reasonable for glibc to hardcode the +0 fallback timezone, rather
than needing the zoneinfo file for it? If so, we could remove tzdata
from minimal containers entirely.
Or is that too naive?
== Benefit to Fedora ==
This change will reduce the size of base container installations.
== Scope ==
* Proposal owners: Implement the proposal.
* Other developers: Developers need to ensure that their packages
continue to build and install with the new split tzdata/tzdata-minimal
package changes.
* Release engineering: No coordination required with Release Engineering.
* Policies and guidelines: The policies and guidelines do not need to
be updated.
* Trademark approval: N/A (not needed for this Change)
* Alignment with Objectives: N/A
== Upgrade/compatibility impact ==
The only visible change will be a new package tzdata-minimal required
by tzdata.
== How To Test ==
Run a dnf upgrade of tzdata and observe that tzdata-minimal is now
also installed as a dependency.
== User Experience ==
Users will see that new updates to tzdata include a new package
dependency on tzdata-minimal.
== Dependencies ==
This change does not require or depend on changes to other packages.
However, we hope that dependent packages will work towards
recommending tzdata for builds and installs rather than requiring it.
== Contingency Plan ==
* Contingency mechanism: If we are unable to complete this feature by
the final development freeze, we will revert to the shipped
configuration.
* Contingency deadline: 100% Code complete deadline
* Blocks release? No
== Documentation ==
No documentation changes are needed at this time.
== Release Notes ==
The tzdata package is now divided into a UTC only package,
tzdata-minimal, and tzdata.
What is supposed to be in tzdata-minimal? Is it
/usr/share/zoneinfo/UTC or that and more?
Forcibly removing tzdata on a fresh Fedora VM that I just set up has
the system fall back to UTC, as expected. On this incredibly small
install, tzdata is required glibc-common, python3-libs, and
python3-dateutil. The last one is reasonable, but for all of them I
ask if tzdata is actually a hard dependency or if it can become a weak
dependency and this change proposal could become "make tzdata
something easily removable" rather than creating more tzdata packages.
For python3-libs, I would have no issue with tzdata a weak dependency.
For users of python3-dateutil, I'd suggest using the Python standard
library instead, where possible.
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