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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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