vm-allocator is a crate designed to provide allocation and release strategies
that are needed by the VMM during the lifetime of a virtual machine. Possible
resource types that a VMM could allocate using vm-allocator are MMIO addresses,
PIO addresses, GSI numbers, device IDs.
This crate exports 2 allocators: one for resources that can be represented as integers, and one for addresses. The reason behind having two separate allocators is the need to add semantic meaning to the address allocator, by specifying configuration parameters such as the alignment that do not make sense in the context of IDs.
The main components of the crate are:
IdAllocatorwhich should be used for all resources that can be reduced to an integer type.AddressAllocatorwhich should be used to allocate address ranges in different address spaces. This component is a wrapper overIntervalTreethat adds semantics to address ranges. More details about the inner presentation of the address allocator can be found in the Design Document.
This allocator should be used to allocate resources that can be reduced to an
integer type like legacy GSI numbers or KVM memory slot IDs. The
characteristics of such a resource are represented by the
IdAllocator
struct.
The struct that defines the
IdAllocator
contains the end of the interval that is managed, a field that points at the
next available ID and a
BTreeSet
that is used to store the released IDs. The reason for using a
BTreeSet is
that the average complexity for deletion and insertion is O(log N), offering a
better performance when compared to Vector for example. The entries are sorted,
so we will always use the first available ID.
When allocating a new ID we always try to return the smallest one available. To
do that we first search in the
BTreeSet for
any ID that was released and if we cannot find anything there we return the next
ID from the range that was never allocated.
The
IdAllocator
struct implements methods for allocating and releasing IDs.
Add vm-allocator as a dependency in Cargo.toml
[dependencies]
vm-allocator = "*"Then add extern crate vm-allocator; to the projects crate root.
The VMM using this crate should instantiate an
IdAllocator
object for each resource type they want to manage.
This project is licensed under either of
- Apache License, Version 2.0
- BSD-3-Clause License