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// Copyright 2022 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//go:build amd64 || arm64
// +build amd64 arm64
package xdp
import (
"fmt"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/sync"
)
// TODO(b/240191988): There's some kind of memory corruption bug that occurs
// occasionally. This occured even before TX was supported.
// TODO(b/240191988): We can hold locks for less time if we accept a more
// obtuse API. For example, CompletionQueue.FreeAll doesn't need to hold a
// mutex for its entire duration.
// UMEM is the shared memory area that the kernel and userspace put packets in.
type UMEM struct {
// mem is the mmap'd area shared with the kernel.
mem []byte
// sockfd is the underlying AF_XDP socket.
sockfd uint32
// frameMask masks the lower bits of an adderess to get the frame's
// address.
frameMask uint64
// mu protects frameAddresses and nFreeFrames.
mu sync.Mutex
// frameAddresses is a stack of available frame addresses.
// +checklocks:mu
frameAddresses []uint64
// nFreeFrames is the number of frames available and is used to index
// into frameAddresses.
// +checklocks:mu
nFreeFrames uint32
}
// SockFD returns the underlying AF_XDP socket FD.
func (um *UMEM) SockFD() uint32 {
return um.sockfd
}
// Lock locks the UMEM.
//
// +checklocksacquire:um.mu
func (um *UMEM) Lock() {
um.mu.Lock()
}
// Unlock unlocks the UMEM.
//
// +checklocksrelease:um.mu
func (um *UMEM) Unlock() {
um.mu.Unlock()
}
// FreeFrame returns the frame containing addr to the set of free frames.
//
// The UMEM must be locked during the call to FreeFrame.
//
// +checklocks:um.mu
func (um *UMEM) FreeFrame(addr uint64) {
um.frameAddresses[um.nFreeFrames] = addr
um.nFreeFrames++
}
// AllocFrame returns the address of a frame that can be enqueued to the fill
// or TX queue. It will panic if there are no frames left, so callers must call
// it no more than the number of buffers reserved via TXQueue.Reserve().
//
// The UMEM must be locked during the call to AllocFrame.
//
// +checklocks:um.mu
func (um *UMEM) AllocFrame() uint64 {
um.nFreeFrames--
return um.frameAddresses[um.nFreeFrames] & um.frameMask
}
// Get gets the bytes of the packet pointed to by desc.
func (um *UMEM) Get(desc unix.XDPDesc) []byte {
end := desc.Addr + uint64(desc.Len)
if desc.Addr&um.frameMask != (end-1)&um.frameMask {
panic(fmt.Sprintf("UMEM (%+v) access crosses frame boundaries: %+v", um, desc))
}
return um.mem[desc.Addr:end]
}
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