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Re: [Libguestfs] Perl module versioning



On 08/09/09 15:20, Richard W.M. Jones wrote:
2. While a version number doesn't guarantee the presence of a feature,
it can guarantee the absence of a feature.

I think you may mean this the other way around ...

No, it was just a slightly obtuse phrasing ;) An old version number can guarantee the absence of a feature. i.e. it can be guaranteed to be definitely too old.


So it's still meaningful to say that my program requires version
x.y.z, although it may also require other things.

3. When faced with a program not working because feature X is absent, it
would be help to know if you need to upgrade to a new libguestfs, or fix
the one you've got.

Yeah, I think the RPM dependency issue is a strong point.  We must
avoid installing sets of RPMs which fail.

The alternative to version numbers is some sort of fine-grained
dependency:

   Provides: perl(Sys::Guestfs::Lib::inspect_linux_kernel)

but that's a lot of work.

Yeah, that's definitely not worth it.

So I think adding a version number to Sys::Guestfs::Lib (which is not
generated) should help, but not to Sys::Guestfs.

I would also add a version to Sys::Guestfs. As you point out, this isn't enough to guarantee that it will work, but it can exclude a large class of cases which definitely won't work. It will also give a much more useful error in this case.

In practise, given that distributors are unlikely to package libguestfs without all the features enabled, I would expect it to exclude *all* cases which don't work.

Matt
--
Matthew Booth, RHCA, RHCSS
Red Hat Engineering, Virtualisation Team

M:       +44 (0)7977 267231
GPG ID:  D33C3490
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