Re: Getting rid of (many) dynamic link creations in the xen build

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.10.2020 22:52, Andrew Cooper wrote:
> On 15/10/2020 11:41, Jürgen Groß wrote:
>> On 15.10.20 12:09, Jan Beulich wrote:
>>> On 15.10.2020 09:58, Jürgen Groß wrote:
>>>> After a short discussion on IRC yesterday I promised to send a mail
>>>> how I think we could get rid of creating dynamic links especially
>>>> for header files in the Xen build process.
>>>>
>>>> This will require some restructuring, the amount will depend on the
>>>> selected way to proceed:
>>>>
>>>> - avoid links completely, requires more restructuring
>>>> - avoid only dynamically created links, i.e. allowing some static
>>>>     links which are committed to git
>>>
>>> While I like the latter better, I'd like to point out that not all
>>> file systems support symlinks, and hence the repo then couldn't be
>>> stored on (or the tarball expanded onto) such a file system. Note
>>> that this may be just for viewing purposes - I do this typically at
>>> home -, i.e. there's no resulting limitation from the build process
>>> needing symlinks. Similarly, once we fully support out of tree
>>> builds, there wouldn't be any restriction from this as long as just
>>> the build tree is placed on a capable file system.
>>>
>>> As a result I'd like to propose variant 2´: Reduce the number of
>>> dynamically created symlinks to a minimum. This said, I have to
>>> admit that I haven't really understood yet why symlinks are bad.
>>> They exist for exactly such purposes, I would think.
>>
>> Not the symlinks as such, but the dynamically created ones seem to be
>> a problem, as we stumble upon those again and again.
> 
> We have multiple build system bugs every release to do with dynamically
> generated symlinks.  Given that symlinks aren't a hard requirement, this
> is a massive price to pay, and time which could be better spent doing
> other other things.
> 
> Also, they prohibit the ability to build from a read-only source dir.

In which way? In an out-of-tree build (see Linux) this gets created
in the build tree, not the source one. Or else ...

> The asm symlink in particular prevents any attempt to do concurrent
> builds of xen.  In some future, I'd love to be able to do concurrent
> out-of-tree builds of Xen on different architectures, because elapsed
> time to do this is one limiting factor of mine on pre-push sanity checks.

... this wouldn't already be possible there (including varying arch-es
built from the same source tree).

Jan