vcpugetfd

vcpugetfd is a term used in some virtualization codebases to refer to a helper function or macro that returns a file descriptor for a virtual CPU (vCPU). In KVM-based virtualization, each vCPU is represented to user space by its own file descriptor; this enables the user-space process to run, inspect, and configure the vCPU independently of other vCPUs.

Typical usage and semantics: the function accepts a VM handle (often a VM file descriptor or a wrapper object) and a vCPU index, and it returns an integer Unix file descriptor that refers to the requested vCPU. The returned FD can then be used with KVM ioctls such as KVM_RUN, KVM_GET_REGS, KVM_SET_REGS, and other per-vCPU operations, or integrated with event loops via poll or epoll.

Implementation notes: in different projects, vcpugetfd may duplicate an existing vCPU FD, or it may obtain a dedicated descriptor from the hypervisor through an internal API. The exact mechanism is project-specific; the Linux kernel's KVM API does not define a canonical vcpugetfd symbol.

Scope and limitations: vcpugetfd is not part of the core Linux kernel API. Its availability and behavior depend on the virtualization project or library being used (for example, QEMU, libvirt, or a custom user-space tool). Because of this, code that uses vcpugetfd in one project may require adaptation to compile or run in another environment.

See also: KVM, QEMU, libvirt, virtualization, vCPU, KVM_RUN, KVM_GET_REGS.