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// Copyright 2018 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.
package pipe
import (
"sync"
"gvisor.googlesource.com/gvisor/pkg/sentry/safemem"
)
// buffer encapsulates a queueable byte buffer.
//
// Note that the total size is slightly less than two pages. This
// is done intentionally to ensure that the buffer object aligns
// with runtime internals. We have no hard size or alignment
// requirements. This two page size will effectively minimize
// internal fragmentation, but still have a large enough chunk
// to limit excessive segmentation.
//
// +stateify savable
type buffer struct {
data [8144]byte
read int
write int
bufferEntry
}
// Reset resets internal data.
//
// This must be called before use.
func (b *buffer) Reset() {
b.read = 0
b.write = 0
}
// Empty indicates the buffer is empty.
//
// This indicates there is no data left to read.
func (b *buffer) Empty() bool {
return b.read == b.write
}
// Full indicates the buffer is full.
//
// This indicates there is no capacity left to write.
func (b *buffer) Full() bool {
return b.write == len(b.data)
}
// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
func (b *buffer) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
dst := safemem.BlockSeqOf(safemem.BlockFromSafeSlice(b.data[b.write:]))
n, err := safemem.CopySeq(dst, srcs)
b.write += int(n)
return n, err
}
// ReadToBlocks implements safemem.Reader.ReadToBlocks.
func (b *buffer) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
src := safemem.BlockSeqOf(safemem.BlockFromSafeSlice(b.data[b.read:b.write]))
n, err := safemem.CopySeq(dsts, src)
b.read += int(n)
return n, err
}
// bufferPool is a pool for buffers.
var bufferPool = sync.Pool{
New: func() interface{} {
return new(buffer)
},
}
// newBuffer grabs a new buffer from the pool.
func newBuffer() *buffer {
b := bufferPool.Get().(*buffer)
b.Reset()
return b
}
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