127 lines
3.8 KiB
Go
127 lines
3.8 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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"log"
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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 = 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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// The offset into payload to which we're currently writing.
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payloadOffset int
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header [OutMessageHeaderSize]byte
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payload [MaxReadSize]byte
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}
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// Make sure that the header field is aligned correctly for
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// fusekernel.OutHeader type punning.
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func init() {
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a := unsafe.Alignof(OutMessage{})
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o := unsafe.Offsetof(OutMessage{}.header)
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e := unsafe.Alignof(fusekernel.OutHeader{})
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if a%e != 0 || o%e != 0 {
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log.Panicf("Bad alignment or offset: %d, %d, need %d", a, o, e)
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}
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}
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// Make sure that the header and payload are contiguous.
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func init() {
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a := unsafe.Offsetof(OutMessage{}.header) + OutMessageHeaderSize
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b := unsafe.Offsetof(OutMessage{}.payload)
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if a != b {
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log.Panicf(
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"header ends at offset %d, but payload starts at offset %d",
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a, b)
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}
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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.payloadOffset = 0
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memclr(unsafe.Pointer(&m.header), OutMessageHeaderSize)
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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() (h *fusekernel.OutHeader)
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// Grow grows m's buffer by the given number of bytes, returning a pointer to
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// the start of the new segment, which is guaranteed to be zeroed. If there is
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// insufficient space, it returns nil.
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func (b *OutMessage) Grow(n int) (p unsafe.Pointer)
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// GrowNoZero is equivalent to Grow, except the new segment is not zeroed. Use
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// with caution!
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func (b *OutMessage) GrowNoZero(n int) (p unsafe.Pointer)
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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 (b *OutMessage) ShrinkTo(n int)
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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 (b *OutMessage) Append(src []byte) {
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p := b.GrowNoZero(len(src))
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if p == nil {
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panic(fmt.Sprintf("Can't grow %d bytes", len(src)))
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}
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sh := (*reflect.SliceHeader)(unsafe.Pointer(&src))
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memmove(p, unsafe.Pointer(sh.Data), uintptr(sh.Len))
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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 (b *OutMessage) AppendString(src string) {
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p := b.GrowNoZero(len(src))
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if p == nil {
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panic(fmt.Sprintf("Can't grow %d bytes", len(src)))
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}
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sh := (*reflect.StringHeader)(unsafe.Pointer(&src))
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memmove(p, unsafe.Pointer(sh.Data), uintptr(sh.Len))
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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 (b *OutMessage) Len() int {
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return int(b.offset)
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}
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// Bytes returns a reference to the current contents of the buffer, including
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// the leading header.
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func (b *OutMessage) Bytes() []byte {
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return b.storage[:int(b.offset)]
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}
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