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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"
- "io"
- "syscall"
- "unsafe"
- "github.com/jacobsa/fuse/internal/fusekernel"
- )
- // All requests read from the kernel, without data, are shorter than
- // this.
- const pageSize = 4096
- func init() {
- // Confirm the page size.
- if syscall.Getpagesize() != pageSize {
- panic(fmt.Sprintf("Page size is unexpectedly %d", syscall.Getpagesize()))
- }
- }
- // We size the buffer to have enough room for a fuse request plus data
- // associated with a write request.
- const bufSize = pageSize + MaxWriteSize
- // An incoming message from the kernel, including leading fusekernel.InHeader
- // struct. Provides storage for messages and convenient access to their
- // contents.
- type InMessage struct {
- remaining []byte
- storage [bufSize]byte
- }
- // Initialize with the data read by a single call to r.Read. The first call to
- // Consume will consume the bytes directly after the fusekernel.InHeader
- // struct.
- func (m *InMessage) Init(r io.Reader) (err error) {
- n, err := r.Read(m.storage[:])
- if err != nil {
- return
- }
- // Make sure the message is long enough.
- const headerSize = unsafe.Sizeof(fusekernel.InHeader{})
- if uintptr(n) < headerSize {
- err = fmt.Errorf("Unexpectedly read only %d bytes.", n)
- return
- }
- m.remaining = m.storage[headerSize:n]
- // Check the header's length.
- if int(m.Header().Len) != n {
- err = fmt.Errorf(
- "Header says %d bytes, but we read %d",
- m.Header().Len,
- n)
- return
- }
- return
- }
- // Return a reference to the header read in the most recent call to Init.
- func (m *InMessage) Header() (h *fusekernel.InHeader) {
- h = (*fusekernel.InHeader)(unsafe.Pointer(&m.storage[0]))
- return
- }
- // Return the number of bytes left to consume.
- func (m *InMessage) Len() uintptr {
- return uintptr(len(m.remaining))
- }
- // Consume the next n bytes from the message, returning a nil pointer if there
- // are fewer than n bytes available.
- func (m *InMessage) Consume(n uintptr) (p unsafe.Pointer) {
- if m.Len() == 0 || n > m.Len() {
- return
- }
- p = unsafe.Pointer(&m.remaining[0])
- m.remaining = m.remaining[n:]
- return
- }
- // Equivalent to Consume, except returns a slice of bytes. The result will be
- // nil if Consume would fail.
- func (m *InMessage) ConsumeBytes(n uintptr) (b []byte) {
- if n > m.Len() {
- return
- }
- b = m.remaining[:n]
- m.remaining = m.remaining[n:]
- return
- }
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