Re: [PATCH 21/31] util: Add iova_tree_alloc

[Peter Xu]

On Tue, Jan 25, 2022 at 10:40:01AM +0100, Eugenio Perez Martin wrote:
> So I think that the first step to remove complexity from the old one
> is to remove iova_begin and iova_end.
> 
> As Jason points out, removing iova_end is easier. It has the drawback
> of having to traverse all the list beyond iova_end, but a well formed
> iova tree should contain none. If the guest can manipulate it, it's
> only hurting itself adding nodes to it.
> 
> It's possible to extract the check for hole_right (or this in Jason's
> proposal) as a special case too.
> 
> But removing the iova_begin parameter is more complicated. We cannot
> know if it's a valid hole without knowing iova_begin, and we cannot
> resume traversing. Could we assume iova_begin will always be 0? I
> think not, the vdpa device can return anything through syscall.

Frankly I don't know what's the syscall you're talking about, but after a 2nd
thought and after I went back and re-read your previous version more carefully
(the one without the list) I think it seems working to me in general.  I should
have tried harder when reviewing the first time!

I mean this one:

https://lore.kernel.org/qemu-devel/20211029183525.1776416-24-eperezma@redhat.com/

Though this time I have some comments on the details.

Personally I like that one (probably with some amendment upon the old version)
more than the current list-based approach.  But I'd like to know your thoughts
too (including Jason).  I'll further comment in that thread soon.

Thanks,

-- 
Peter Xu