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Re: repotags proposal



On Wed, 23 May 2007, Dag Wieers wrote:

On Wed, 23 May 2007, Tim Lauridsen wrote:

Panu Matilainen wrote:

My 5c on the topic I've been trying to avoid because it's too flammable for
my taste. I hate politics so I'm not going to get into that, I'm commenting
from purely technical POV, and actually have a proposal that might make them
unnecessary.

Repotags as part of release string are just plain wrong. Unlike disttag, the
repotag does not have a meaningful version information in it, it's really
just a fuzz-factor to somehow differentiate packages coming from different
places.

It does have meaningful version information in a multi-repository world.
It shows what version of the package you have. rf means this is the
RPMforge version. It makes the package/filename/version unique !

Actually you could make the package filename contain a repotag just by tweaking %_build_name_fmt macro on the buildsystem. The packages themselves have plenty of uniquely identifying data in them, strongest of which is the signature (if present). It's just that the current tools dont allow using the data to full extent.

Granted, the repotag does not have any real meaning in "version
comparison" between packages from different repositories. Neither does the
release tag. The release tag has no meaningful version information between
packages from different repositories.

Indeed (in the "is another package newer" sense) - like you noted it does have a meaning in non-automatic, versioned (sub-)package dependencies.

The perfect repotag would actually be the package's gpg signature:
- it's not involved in version comparison
- it can't be faked by locally rebuilding a package - it's recorded in rpmdb
so it's possible to see where a package came from

It is not a perfect repotag for other reasons:
- It doesn't make the filename unique (or gives insight of the package
 before downloading)
- It is not shown when one has dependency problems, either on yum, apt or
 rpm level

See above, filename "uniqueness" is easily solvable. Making a human-friendly signature visible in the tools obviously requires some modifications to the tools. So it might not help RHEL 2.1 or Fedora 7, but I'd rather try and start fixing the problems so I don't have to read about repotag arguments five years from now.

For depsolvers, you need some sort of priorisation mechanism anyway to make
any sense out of mixed repository situation. So the repotag mostly serves as
a visual clue to humans. All the major depsolvers now have some means to
priorize between repositories so what the actual rpm EVR string is doesn't
really matter, what's missing is the visual clue.

The major depsolvers lack a meaningful way for a user to provide a policy
of what they want to do with repositories or packages. Some plugins do
allow somewhat more, but there are many shortcomings and without repotags
errors are at first sight inexplicable or confusing.

Especially when packages from different repositories have the same NEVR,
similar sub-packages and have dependencies between them.

The clamav package is a nice example. Without repotags, dependencies would
exists between packages from different repositories.

Yup. See my other mail for an idea wrt this. Again, wont help you for existing releases.

But that's just part of the problem... manual, versioned dependencies are a minority in the package dependency data, the vast majority is automatically generated soname dependencies where there are no repotags and things can (and do) get pretty mixed up easily. It might help if yum etc could try to first resolve dependencies from the same repo where the dependency itself comes from.

Saying that repotags have no meaningful version information is very wrong.
It makes the system work.

"Prevents the system from totally blowing up" would be closer to reality I think :)

Now, I hereby volunteer to write a script/popt-alias/whatever that will do
the necessary mapping of gpg signature into something human readable so
people can diagnose their repo-mixing problems and whatnot easily. So you'd
get something resembling the below:

$ repotag -q foo bar
foo-1.2-4.el5 (EPEL)
bar-2.3-1.el5 (ATrpms)

Would something like that be enough for the "repotag folks", short term?

Look like a great idea, do you plan to do at standalone tool or something
based on the the Yum API, it sounds like a candidate to
yum-utils.

It doesn't help for dependency problems. In this case it shows what a
working rpmdb consists of. Necessary, but not sufficient to replace a
repotag implementation as it is.

Right.

Long-term, more than that's needed to really solve the issues with
repository mixing. One (perhaps crazy) idea is turning repotags into
namespaces, and dependencies are first looked up within that namespace and
only if unsolved, other namespaces are looked at in (configurable) order.

An example (please excuse the :: notation, that's not a good choice but for
examples sake...): assume we have packages foo and bar which both depend on
glibc, and foo additionally depends on bar. Foo and bar are available from,
say, both EPEL and ATrpms:

rhel::libxml2-2.6.28-1
epel::foo-1.2-1
atrpms::foo-1.2-1
epel::bar-2.4-5
atrpms::bar-2.4-1

If you install atrpms::foo, as atrpms namespace also provides bar, that one
gets selected instead of epel::bar even though it's evr is higher. The
actual namespace could internally be the gpg signature, only mapped to a
human readable where exposed to the user. Sound crazy enough? ;)

Yes, i sounds very crazy to me ;-) ;-) .
I dont know if this can be done without a lot of changes into RPM.

The namespace idea is an interesting one and when it gets implemented and
is ready is surely an alternative to repotags.

But it is not ready and will not be in EL2.1, EL3, EL4 or EL5. So we
cannot consider it an alternative because we cannot use it now.

It's not that I'm unwilling to see an alternative, it's just that there is
NO alternative to repotags that cover it's different uses.

Nice to see something constructive to solve the real problems.

It doesn't solve real problems as it is not a realistic solution yet.

Yes, I don't have a solution, but repotags are not a solution either, just a bandaid. I'd rather attempt to have a constructive discussion how to solve the bleeping problems for good. But this isn't the best forum for that discussion, going crazy with package/dependency namespaces and whatnot concerns far more people than are involved in epel...

	- Panu -


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