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- // Copyright 2015 Google Inc. All Rights Reserved.
- //
- // 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 buffer
- import (
- "fmt"
- "log"
- "reflect"
- "unsafe"
- "github.com/jacobsa/fuse/internal/fusekernel"
- )
- // OutMessageHeaderSize is the size of the leading header in every
- // properly-constructed OutMessage. Reset brings the message back to this size.
- const OutMessageHeaderSize = int(unsafe.Sizeof(fusekernel.OutHeader{}))
- // OutMessage provides a mechanism for constructing a single contiguous fuse
- // message from multiple segments, where the first segment is always a
- // fusekernel.OutHeader message.
- //
- // Must be initialized with Reset.
- type OutMessage struct {
- // The offset into payload to which we're currently writing.
- payloadOffset int
- header fusekernel.OutHeader
- payload [MaxReadSize]byte
- }
- // Make sure that the header and payload are contiguous.
- func init() {
- a := unsafe.Offsetof(OutMessage{}.header) + uintptr(OutMessageHeaderSize)
- b := unsafe.Offsetof(OutMessage{}.payload)
- if a != b {
- log.Panicf(
- "header ends at offset %d, but payload starts at offset %d",
- a, b)
- }
- }
- // Reset resets m so that it's ready to be used again. Afterward, the contents
- // are solely a zeroed fusekernel.OutHeader struct.
- func (m *OutMessage) Reset() {
- // Ideally we'd like to write:
- //
- // m.payloadOffset = 0
- // m.header = fusekernel.OutHeader{}
- //
- // But Go 1.8 beta 2 generates bad code for this
- // (https://golang.org/issue/18370). Encourage it to generate the same code
- // as Go 1.7.4 did.
- //if unsafe.Offsetof(m.payload) != 24 {
- // panic("unexpected OutMessage layout")
- //}
- //a := (*[3]uint64)(unsafe.Pointer(m))
- //a[0] = 0
- //a[1] = 0
- //a[2] = 0
- m.payloadOffset = 0
- m.header = fusekernel.OutHeader{}
- }
- // OutHeader returns a pointer to the header at the start of the message.
- func (m *OutMessage) OutHeader() *fusekernel.OutHeader {
- return &m.header
- }
- // Grow grows m's buffer by the given number of bytes, returning a pointer to
- // the start of the new segment, which is guaranteed to be zeroed. If there is
- // insufficient space, it returns nil.
- func (m *OutMessage) Grow(n int) (p unsafe.Pointer) {
- p = m.GrowNoZero(n)
- if p != nil {
- memclr(p, uintptr(n))
- }
- return
- }
- // GrowNoZero is equivalent to Grow, except the new segment is not zeroed. Use
- // with caution!
- func (m *OutMessage) GrowNoZero(n int) (p unsafe.Pointer) {
- // Will we overflow the buffer?
- o := m.payloadOffset
- if len(m.payload)-o < n {
- return
- }
- p = unsafe.Pointer(uintptr(unsafe.Pointer(&m.payload)) + uintptr(o))
- m.payloadOffset = o + n
- return
- }
- // ShrinkTo shrinks m to the given size. It panics if the size is greater than
- // Len() or less than OutMessageHeaderSize.
- func (m *OutMessage) ShrinkTo(n int) {
- if n < OutMessageHeaderSize || n > m.Len() {
- panic(fmt.Sprintf(
- "ShrinkTo(%d) out of range (current Len: %d)",
- n,
- m.Len()))
- }
- m.payloadOffset = n - OutMessageHeaderSize
- }
- // Append is equivalent to growing by len(src), then copying src over the new
- // segment. Int panics if there is not enough room available.
- func (m *OutMessage) Append(src []byte) {
- p := m.GrowNoZero(len(src))
- if p == nil {
- panic(fmt.Sprintf("Can't grow %d bytes", len(src)))
- }
- sh := (*reflect.SliceHeader)(unsafe.Pointer(&src))
- memmove(p, unsafe.Pointer(sh.Data), uintptr(sh.Len))
- return
- }
- // AppendString is like Append, but accepts string input.
- func (m *OutMessage) AppendString(src string) {
- p := m.GrowNoZero(len(src))
- if p == nil {
- panic(fmt.Sprintf("Can't grow %d bytes", len(src)))
- }
- sh := (*reflect.StringHeader)(unsafe.Pointer(&src))
- memmove(p, unsafe.Pointer(sh.Data), uintptr(sh.Len))
- return
- }
- // Len returns the current size of the message, including the leading header.
- func (m *OutMessage) Len() int {
- return OutMessageHeaderSize + m.payloadOffset
- }
- // Bytes returns a reference to the current contents of the buffer, including
- // the leading header.
- func (m *OutMessage) Bytes() []byte {
- l := m.Len()
- sh := reflect.SliceHeader{
- Data: uintptr(unsafe.Pointer(&m.header)),
- Len: l,
- Cap: l,
- }
- return *(*[]byte)(unsafe.Pointer(&sh))
- }
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