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Re: [MirageOS-devel] xen event channels, grants, block devices etc

On Tue, Jan 21, 2014 at 9:48 PM, Anil Madhavapeddy <anil@xxxxxxxxxx> wrote:
On 21 Jan 2014, at 21:31, David Scott <scott.dj@xxxxxxxxx> wrote:

NB: I think I'm hitting an opam 1.1.0-beta bug where "mirage-types" optionally depends on "lwt & ipaddr"; some other package depends on "lwt"; but "ipaddr" is not being demanded. Anyone else seeing this? Perhaps I've misunderstood the meaning of depopts in opam. A workaround is just to install "ipaddr" first.

The intention here is to have:

- a 'mirage-types' package that is completely dependency free, and only has module type definitions with completely abstract types.
- a 'mirage-types.lwt' package which specializes the above types with some concrete common defaults, specifically Lwt for IO and Cstruct for buffer, Ipaddr.V4.t for ipaddr.  Because these are concrete types in the module signature, you now need those libraries installed to get the cmi files for them.

The OPAM line of:

depopts: [ ("lwt" & "cstruct" & "ipaddr") ]

means that if all three of the packages are present, then an optional dependency (the mirage-types.lwt) will be compiled.  However, upstream users of mirage-types.lwt will thus need to explicitly depend on lwt/cstruct/ipaddr to ensure that mirage-types.lwt will actually be present.

Ah ok. In my case the BLOCK signature is being used by mirage-block-xen, so I guess I should explicitly add ipaddr to its depends (I'm sure lwt and cstruct are already there). Pity I can't say it depends on 'mirage-types.lwt' -- I guess that would require yet another package.

I notice the new mirage-types.lwt will try to build IFF 'lwt' is present:

Perhaps we should change this to IFF 'lwt & cstruct & ipaddr' so the error manifests as a 'mirage-types.lwt' is missing higher up the dependency chain where the missing dependency on 'ipaddr' is?

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