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ringbuffer.go
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/
ringbuffer.go
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// Copyright 2017 Capsule8, Inc.
//
// 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.
package perf
import (
"errors"
"os"
"sync/atomic"
"unsafe"
"github.com/capsule8/capsule8/pkg/config"
"golang.org/x/sys/unix"
)
type ringBuffer struct {
fd int
memory []byte
metadata *metadata
data []byte
}
func newRingBuffer(fd int, pageCount int) (*ringBuffer, error) {
pageSize := os.Getpagesize()
if pageCount <= 0 {
pageCount = config.Sensor.RingBufferPages
}
memory, err := unix.Mmap(fd, 0, (pageCount+1)*pageSize, unix.PROT_READ|unix.PROT_WRITE, unix.MAP_SHARED)
if err != nil {
return nil, err
}
rb := &ringBuffer{
fd: fd,
memory: memory,
metadata: (*metadata)(unsafe.Pointer(&memory[0])),
data: memory[pageSize:],
}
for {
seq := atomic.LoadUint32(&rb.metadata.Lock)
if seq%2 != 0 {
// seqlock must be even before value is read
continue
}
version := atomic.LoadUint32(&rb.metadata.Version)
compatVersion := atomic.LoadUint32(&rb.metadata.CompatVersion)
if atomic.LoadUint32(&rb.metadata.Lock) != seq {
// seqlock must be even and the same after values have been read
continue
}
if version != 0 || compatVersion != 0 {
return nil, errors.New("Incompatible ring buffer memory layout version")
}
break
}
return rb, nil
}
func (rb *ringBuffer) unmap() error {
return unix.Munmap(rb.memory)
}
func (rb *ringBuffer) timeRunning() uint64 {
return atomic.LoadUint64(&rb.metadata.TimeRunning)
}
// Read calls the given function on each available record in the ringbuffer
func (rb *ringBuffer) read(f func([]byte)) {
var dataHead, dataTail uint64
dataTail = rb.metadata.DataTail
dataHead = atomic.LoadUint64(&rb.metadata.DataHead)
for dataTail < dataHead {
dataBegin := dataTail % uint64(len(rb.data))
dataEnd := dataHead % uint64(len(rb.data))
var data []byte
if dataEnd >= dataBegin {
data = rb.data[dataBegin:dataEnd]
} else {
data = rb.data[dataBegin:]
data = append(data, rb.data[:dataEnd]...)
}
f(data)
//
// Write dataHead to dataTail to let kernel know that we've
// consumed the data up to it.
//
dataTail = dataHead
atomic.StoreUint64(&rb.metadata.DataTail, dataTail)
// Update dataHead in case it has been advanced in the interim
dataHead = atomic.LoadUint64(&rb.metadata.DataHead)
}
}