partial free/split for ds

[Christian Helmuth]

Hello Alexander,

On Mon, Nov 02, 2020 at 23:55:07 CET, Alexander Tormasov via users wrote:
> I have a physical memory which is used for populated managed dataspace, like
>     	Dataspace_capability ds = env.ram().alloc(SIZE);
>         void * base_rw = env.rm().attach(ds);
>         memset(base_rw, 0xff, SIZE);
>         env.rm().detach(base_rw);
> 
> I use it as backend for mmap and found, that I need to be able to change mapping in the standard way which used for this mmap/munmap interface.
> 
> Typically, I want to free a part of this ds, e.g., in the middle of it.
> Like UUUUUU -> UUUFFU (where Used and Free abbreviation used), keeping mapping and content for all old addresses except freed ones, in the «middle» of area [base_rw, base_rw+SIZE) from above.
> 
> How I can do this?
> Probably after operation I will have 2 ds instead of original one;
> Anyway, I do not want to loose the content of old ds during this procedure, 
> and want to get rid of copy of  old content to new one.
> Is it possible to split ds in such a way?
> From code of Region_map_component::detach I see that I can detach only from the beginning of the region.

How about using multiple dataspaces (chunks) in the first place, ie.
each U is a separate dataspace and all dataspaces are mapped into a
consecutive region in virtual memory?

Greets
-- 
Christian Helmuth
Genode Labs

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