GNU/Hurd: use mach debug API to convert virtual addresses to physical

[luckyluke]

This is needed for some drivers e.g. virtio.

[anttikantee]

I think @robertmillan should review & merge this. However, a few comments:

1. it would be nice to use the same indentation style
2. what is the significance of the 256 hardcoded limit?

[luckyluke]

1. you're right, i forced an update of the branch, it should be better now
2. It's an upper bound of what was needed on my tests (with virtio ld driver, reading and writing 512 bytes at a time).

[anttikantee]

Is there no mach_vm call which would actually honor vaddr, or a possibility to loop? (nb. don't take this interrogation as a sign that the patch may be rejected, I just want the patch to be the best it can be with reasonable effort)

[luckyluke]

I think no, at least I couldn't find a better mach_vm call; the only way to get the physical address is using the debug API, which seems to be enabled by default (e.g. on Debian).
Do you mean to loop over chunks of 256 page info at a time, just in case there are more than 256 pages?

[anttikantee]

@robertmillan said in email that he's busy, so I'm merging this now.

@luckyluke are you somehow affiliated with HURD and can push the improvement upstream?

[luckyluke]

@anttikantee I'm not an official developer, however I can ask for comments on HURD channels

[anttikantee]

Thanks!