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// Copyright 2021 The gVisor Authors.
//
// 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 eventfd wraps Linux's eventfd(2) syscall.
package eventfd
import (
"fmt"
"io"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/hostarch"
"gvisor.dev/gvisor/pkg/tcpip/link/rawfile"
)
const sizeofUint64 = 8
// Eventfd represents a Linux eventfd object.
type Eventfd struct {
fd int
}
// Create returns an initialized eventfd.
func Create() (Eventfd, error) {
fd, _, err := unix.RawSyscall(unix.SYS_EVENTFD2, 0, 0, 0)
if err != 0 {
return Eventfd{}, fmt.Errorf("failed to create eventfd: %v", error(err))
}
if err := unix.SetNonblock(int(fd), true); err != nil {
unix.Close(int(fd))
return Eventfd{}, err
}
return Eventfd{int(fd)}, nil
}
// Wrap returns an initialized Eventfd using the provided fd.
func Wrap(fd int) Eventfd {
return Eventfd{fd}
}
// Close closes the eventfd, after which it should not be used.
func (ev Eventfd) Close() error {
return unix.Close(ev.fd)
}
// Dup copies the eventfd, calling dup(2) on the underlying file descriptor.
func (ev Eventfd) Dup() (Eventfd, error) {
other, err := unix.Dup(ev.fd)
if err != nil {
return Eventfd{}, fmt.Errorf("failed to dup: %v", other)
}
return Eventfd{other}, nil
}
// Notify alerts other users of the eventfd. Users can receive alerts by
// calling Wait or Read.
func (ev Eventfd) Notify() error {
return ev.Write(1)
}
// Write writes a specific value to the eventfd.
func (ev Eventfd) Write(val uint64) error {
var buf [sizeofUint64]byte
hostarch.ByteOrder.PutUint64(buf[:], val)
for {
n, err := unix.Write(ev.fd, buf[:])
if err == unix.EINTR {
continue
}
if n != sizeofUint64 {
panic(fmt.Sprintf("short write to eventfd: got %d bytes, wanted %d", n, sizeofUint64))
}
return err
}
}
// Wait blocks until eventfd is non-zero (i.e. someone calls Notify or Write).
func (ev Eventfd) Wait() error {
_, err := ev.Read()
return err
}
// Read blocks until eventfd is non-zero (i.e. someone calls Notify or Write)
// and returns the value read.
func (ev Eventfd) Read() (uint64, error) {
var tmp [sizeofUint64]byte
n, err := rawfile.BlockingReadUntranslated(ev.fd, tmp[:])
if err != 0 {
return 0, err
}
if n == 0 {
return 0, io.EOF
}
if n != sizeofUint64 {
panic(fmt.Sprintf("short read from eventfd: got %d bytes, wanted %d", n, sizeofUint64))
}
return hostarch.ByteOrder.Uint64(tmp[:]), nil
}
// FD returns the underlying file descriptor. Use with care, as this breaks the
// Eventfd abstraction.
func (ev Eventfd) FD() int {
return ev.fd
}
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