Backwards compatibility of the RPM format
avi at scylladb.com
Tue Oct 2 14:36:06 UTC 2018
On 02/10/2018 17.06, Panu Matilainen wrote:
> On 10/2/18 1:10 PM, Avi Kivity wrote:
>> Hi, I'm considering moving from mock to rpmbuild, since
>> simplifications in my build process now allow it and rpmbuild is
>> generally faster.
>> A possible problem is incompatible changes in the format. If I build
>> on Fedora 28+, will the resulting RPM be installable on RHEL? The RPM
>> is self-contained and has no dependencies.
> Depends on which RHEL, and all the other funny little details.
> With a truly self-contained package without external dependencies it
> should be possible to build packages that can be installed on RHEL 3
> even, but it'll require some tweaking.
I already tested Fedora 28 -> RHEL 7. I'm concerned about Fedora 28+K ->
RHEL 7, for increasing values of K.
I'm happy to tweak, as long as the tweaks are documented somewhere.
>> - are the file formats compatible, and will they continue to be
>> compatible? I know that compression algorithms have changed, but
>> perhaps they were backported (or happened early enough to be included
>> in RHEL)
> The fundamental file format is basically unchanged, but like you note
> compression algorithms can differ. Impossible to say anything specific
> about comptibility without exact versions, but even if the older
> version doesn't support compressor X you can always just configure it
> to use good old gzip compression.
> The rpm mechanism for dealing with incompatibilities is rpmlib()
> dependencies, which will prevent installation on a version that does
> not support the features a particular package requires. If such a
> feature gets backported, the same package will become installable.
Can you point me at the documentation for this? I'm not above
trial-and-error tweaking if needed.
>> - are there flags I can specify to tell rpmbuild to restrict itself
>> to an older feature set?
> Not quite like that, but once you know what you're targetting you can
> configure many things to compatible level. For some other features you
> might need to create spec conditionals.
>> - is this a supported practice, or do you recommend against for
> Rpm goes to quite some lengths in the name of compatibility, BUT for
> best results, build on the target distro. That way any
> incompatibilities will be caught at build-time instead of install
> time, fewer hairy details to sort out and so on.
We test the rpm right after building, and in the worst case we just
update the flags and create a new rpm. As long as there commitment to
make it work, rather than it working by accident, I'm happy to use this
method. And it looks like there is.
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