[Pkg-xen-devel] [patch] Packages ocaml libraries

[Jonathan Ludlam]

On 23 Oct 2011, at 11:47, Thomas Goirand wrote:

> On 10/23/2011 05:27 PM, Jon Ludlam wrote:
>> Hi Thomas,
>> 
>> I don't see why the patches shouldn't be back ported - I believe we're
>> the only user of the ocaml bindings, so nobody else should be affected
> 
> What do you mean "backported"? Do you mean take your code change in the
> ocaml, and backport it to current Xen 4.1.1 in SID? I don't see why not,
> but in this case, I think you'd be the best person to take care of that.
> Would a simple copy of the ocaml folder be enough?
> 

I meant to the 4.1-stable branch of xen, for a 4.1.3 release.

>> - certainly nobody on the list commented to that effect when I
>> submitted the patches. However, it *is* a breaking change, so there may
>> be some principles that back porting would violate; we'd have to
>> confirm it with the xen maintainers.
> 
> Well, since the ocaml libraries have never been shipped by the binary
> packages of Xen in Debian, we aren't breaking anything form the Debian
> perspective.
> 

True, but from the perspective of anyone using the ocaml libs in vanilla xen 4.1.2, having them renamed underneath you in a bugfix release is a bit rude. This is all hypothetical of course, since we don't know of any users of the ocaml :-)

>> However, having thought about the layout of the existing debian xen
>> packages, I think that there will be a requirement that the ocaml
>> libraries live under /usr/lib/xen-4.1/lib/ocaml (I think Bastian hinted
>> at this back in July but I didn't spot the implication).
> 
> This whole /usr/lib/xen-<version> thing is only there because Bastian
> wants to maintain it, probably because he wants to be able to install
> more than one Xen hypervisor at the same time (right?). Bastian wants to
> invest time in this, I don't think it is *required* that we do.
> 
> It's a pain to maintain, adds Debian specific patches, put things in
> non-standard directories (with implications for the other packages). And
> one has yet to convince me in what situation it is needed to have more
> than one Xen hypervisor version installed at the same time. I really
> would love to see this "feature" reverted in Debian, unless upstream Xen
> itself starts supporting it…
> 

That's not an argument I want to get in to. As far as I'm concerned, I'd like to try and get the ocaml libraries into debian. I don't really mind so long as I can compile the programs that need to link with them. You'll have to fight that particular battle out with the rest of pkg-xen-devel :-)

>> In a worse-case scenario, we could package up the
>> native libraries only.
> 
> What do you call the "native libraries"?
> 

Ocaml libraries come in two flavours - byte-code and native. The bytecode libs are run on the ocaml virtual machine (ocamlrun) and the native ones are effectively ahead-of-time compiled. The differ in the way that the C libraries that they depend on are linked in.

The big issue is that, due to the Debian recommendation against using rpaths, the Debian ocaml packages have patches in to remove the ability to specify rpaths, which makes things tricky when the libraries you're trying to link against are stored outside of the usual places.

Anyway, the problem isn't insurmountable, and as I said, if we could only get the native libraries to work properly then that's no big deal. Xapi uses native compilation exclusively, so it won't hurt us.
  
Jon