85 lines
2.5 KiB
Go
85 lines
2.5 KiB
Go
// Copyright 2020 The gVisor Authors.
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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 hostfd provides efficient I/O with host file descriptors.
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package hostfd
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import (
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"gvisor.dev/gvisor/pkg/safemem"
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"gvisor.dev/gvisor/pkg/sync"
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)
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// ReadWriterAt implements safemem.Reader and safemem.Writer by reading from
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// and writing to a host file descriptor respectively. ReadWriterAts should be
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// obtained by calling GetReadWriterAt.
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//
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// Clients should usually prefer to use Preadv2 and Pwritev2 directly.
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type ReadWriterAt struct {
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fd int32
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offset int64
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flags uint32
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}
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var rwpool = sync.Pool{
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New: func() interface{} {
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return &ReadWriterAt{}
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},
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}
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// GetReadWriterAt returns a ReadWriterAt that reads from / writes to the given
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// host file descriptor, starting at the given offset and using the given
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// preadv2(2)/pwritev2(2) flags. If offset is -1, the host file descriptor's
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// offset is used instead. Users are responsible for ensuring that fd remains
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// valid for the lifetime of the returned ReadWriterAt, and must call
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// PutReadWriterAt when it is no longer needed.
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func GetReadWriterAt(fd int32, offset int64, flags uint32) *ReadWriterAt {
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rw := rwpool.Get().(*ReadWriterAt)
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*rw = ReadWriterAt{
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fd: fd,
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offset: offset,
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flags: flags,
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}
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return rw
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}
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// PutReadWriterAt releases a ReadWriterAt returned by a previous call to
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// GetReadWriterAt that is no longer in use.
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func PutReadWriterAt(rw *ReadWriterAt) {
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rwpool.Put(rw)
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}
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// ReadToBlocks implements safemem.Reader.ReadToBlocks.
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func (rw *ReadWriterAt) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
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if dsts.IsEmpty() {
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return 0, nil
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}
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n, err := Preadv2(rw.fd, dsts, rw.offset, rw.flags)
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if rw.offset >= 0 {
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rw.offset += int64(n)
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}
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return n, err
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}
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// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
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func (rw *ReadWriterAt) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
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if srcs.IsEmpty() {
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return 0, nil
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}
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n, err := Pwritev2(rw.fd, srcs, rw.offset, rw.flags)
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if rw.offset >= 0 {
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rw.offset += int64(n)
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}
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return n, err
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}
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