repotags proposal

Panu Matilainen pmatilai at laiskiainen.org
Thu May 24 13:52:58 UTC 2007


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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