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// Copyright 2018 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.
// +build linux
package fdnotifier
import (
"unsafe"
"golang.org/x/sys/unix"
"gvisor.dev/gvisor/pkg/waiter"
)
// NonBlockingPoll polls the given FD in non-blocking fashion. It is used just
// to query the FD's current state.
func NonBlockingPoll(fd int32, mask waiter.EventMask) waiter.EventMask {
e := struct {
fd int32
events int16
revents int16
}{
fd: fd,
events: int16(mask.ToLinux()),
}
ts := unix.Timespec{
Sec: 0,
Nsec: 0,
}
for {
n, _, err := unix.RawSyscall6(unix.SYS_PPOLL, uintptr(unsafe.Pointer(&e)), 1,
uintptr(unsafe.Pointer(&ts)), 0, 0, 0)
// Interrupted by signal, try again.
if err == unix.EINTR {
continue
}
// If an error occur we'll conservatively say the FD is ready for
// whatever is being checked.
if err != 0 {
return mask
}
// If no FDs were returned, it wasn't ready for anything.
if n == 0 {
return 0
}
// Otherwise we got the ready events in the revents field.
return waiter.EventMaskFromLinux(uint32(e.revents))
}
}
// epollWait performs a blocking wait on epfd.
//
// Preconditions: len(events) > 0
func epollWait(epfd int, events []unix.EpollEvent, msec int) (int, error) {
if len(events) == 0 {
panic("Empty events passed to EpollWait")
}
// We actually use epoll_pwait with NULL sigmask instead of epoll_wait
// since that is what the Go >= 1.11 runtime prefers.
r, _, e := unix.Syscall6(unix.SYS_EPOLL_PWAIT, uintptr(epfd), uintptr(unsafe.Pointer(&events[0])), uintptr(len(events)), uintptr(msec), 0, 0)
if e != 0 {
return 0, e
}
return int(r), nil
}
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