Provide a specialized interval tree for resource management

[jiangliu]

This PR implements a specialized version of interval tree for resource management, which could be used manage normal VMM resources.

[liujing2]

It seems this function needs more parameters?

[jiangliu]

It's used to cover the most common usage scenario. For rare use cases, you may dirrectly construct a Constraint object or we may add some new interfaces for those cases.

[liujing2]

So what is the difference between this and ResourceConstraint defined in rust-vmm/vm-device#9 ?

[jiangliu]

It's two related abstractions. With Device::ResourceConstraint and vm_allocator::Constraint, there's still one piece missing of the whole puzzle. We need the vmm to implement a resource manager, which converts Device::ResourceConstraint to vm_allocator::Constraint.

1. vm_allocator is just a generic resource allocator,
2. vmm::ResourceManager needs to define type of resources and use vm_allocator to manage its resources.
   It's still unclear whether vmm::ResourceManager should be VMM specific or we need another vmm_resource crate.

[liujing2]

It's two related abstractions. With Device::ResourceConstraint and vm_allocator::Constraint, there's still one piece missing of the whole puzzle. We need the vmm to implement a resource manager, which converts Device::ResourceConstraint to vm_allocator::Constraint.

Ok, this is the "glue" part between vm-device and vm-allocator.

1. vm_allocator is just a generic resource allocator,
2. vmm::ResourceManager needs to define type of resources and use vm_allocator to manage its resources.
   It's still unclear whether vmm::ResourceManager should be VMM specific or we need another vmm_resource crate.

I think we also need a conversion from the vmm::ResourceManager::allocate_resources() return type to vm_device::Resource for registering devices.

[jiangliu]

Yes, that's true. Interval tree just manages a set of IDs, the resource manager needs to define the specific resources the ID stands for.

[sameo]

Before looking deeper into the actual code, I guess my first general question would be: why couldn't we use one of the existing rust collection structure as the inner IntervalTree tree structure:

struct IntervalTree<T> {
          root: BTreeMap<Range, T>>,          
}

[jiangliu]

Before looking deeper into the actual code, I guess my first general question would be: why couldn't we use one of the existing rust collection structure as the inner IntervalTree tree structure:

struct IntervalTree<T> {
          root: BTreeMap<Range, T>>,          
}

IntervalTree supports using range(start, end) as the key, so we could search the entry containing a specific value(point).
We want to avoid this

    fn first_before(&self, addr: u64) -> Option<(BusRange, &Mutex<dyn BusDevice>)> {
        // for when we switch to rustc 1.17: self.devices.range(..addr).iter().rev().next()
        for (range, dev) in self.devices.iter().rev() {
            if range.0 <= addr {
                return Some((*range, dev));
            }
        }
        None
    }

[AlexandruCihodaru]

Closing this as it is obsolete.