128 lines
3.6 KiB
Go
128 lines
3.6 KiB
Go
// Copyright 2015 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package buffer
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import (
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"fmt"
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"reflect"
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"unsafe"
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"github.com/jacobsa/fuse/internal/fusekernel"
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)
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// OutMessageHeaderSize is the size of the leading header in every
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// properly-constructed OutMessage. Reset brings the message back to this size.
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const OutMessageHeaderSize = int(unsafe.Sizeof(fusekernel.OutHeader{}))
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// OutMessage provides a mechanism for constructing a single contiguous fuse
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// message from multiple segments, where the first segment is always a
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// fusekernel.OutHeader message.
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//
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// Must be initialized with Reset.
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type OutMessage struct {
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header fusekernel.OutHeader
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Sglist [][]byte
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}
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// Reset resets m so that it's ready to be used again. Afterward, the contents
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// are solely a zeroed fusekernel.OutHeader struct.
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func (m *OutMessage) Reset() {
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m.header = fusekernel.OutHeader{}
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m.Sglist = nil
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}
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// OutHeader returns a pointer to the header at the start of the message.
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func (m *OutMessage) OutHeader() *fusekernel.OutHeader {
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return &m.header
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}
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// Grow adds a new buffer of <n> bytes to the message, returning a pointer to
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// the start of the new segment, which is guaranteed to be zeroed.
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func (m *OutMessage) Grow(n int) unsafe.Pointer {
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b := make([]byte, n)
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m.Append(b)
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p := unsafe.Pointer(&b[0])
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return p
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}
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// ShrinkTo shrinks m to the given size. It panics if the size is greater than
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// Len() or less than OutMessageHeaderSize.
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func (m *OutMessage) ShrinkTo(n int) {
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if n < OutMessageHeaderSize || n > m.Len() {
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panic(fmt.Sprintf(
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"ShrinkTo(%d) out of range (current Len: %d)",
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n,
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m.Len()))
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}
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if n == OutMessageHeaderSize {
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m.Sglist = nil
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} else {
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i := 1
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n -= OutMessageHeaderSize
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for len(m.Sglist) > i && n >= len(m.Sglist[i]) {
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n -= len(m.Sglist[i])
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i++
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}
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if n > 0 {
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m.Sglist[i] = m.Sglist[i][0:n]
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i++
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}
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m.Sglist = m.Sglist[0:i]
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}
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}
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// Append is equivalent to growing by len(src), then copying src over the new
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// segment. Int panics if there is not enough room available.
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func (m *OutMessage) Append(src ...[]byte) {
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if m.Sglist == nil {
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// First element of Sglist is pre-filled with a pointer to the header
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// to allow sending it with a single writev() call without copying the
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// slice again
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m.Sglist = append(m.Sglist, m.OutHeaderBytes())
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}
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m.Sglist = append(m.Sglist, src...)
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return
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}
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// AppendString is like Append, but accepts string input.
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func (m *OutMessage) AppendString(src string) {
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m.Append([]byte(src))
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return
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}
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// Len returns the current size of the message, including the leading header.
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func (m *OutMessage) Len() int {
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if m.Sglist == nil {
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return OutMessageHeaderSize
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}
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// First element of Sglist is the header, so we don't need to count it here
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r := 0
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for _, b := range m.Sglist {
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r += len(b)
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}
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return r
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}
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// OutHeaderBytes returns a byte slice containing the current header.
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func (m *OutMessage) OutHeaderBytes() []byte {
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l := OutMessageHeaderSize
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sh := reflect.SliceHeader{
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Data: uintptr(unsafe.Pointer(&m.header)),
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Len: l,
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Cap: l,
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}
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return *(*[]byte)(unsafe.Pointer(&sh))
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}
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