github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/fdnotifier/poll_unsafe.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  // +build linux
    16  
    17  package fdnotifier
    18  
    19  import (
    20  	"unsafe"
    21  
    22  	"golang.org/x/sys/unix"
    23  	"github.com/SagerNet/gvisor/pkg/waiter"
    24  )
    25  
    26  // NonBlockingPoll polls the given FD in non-blocking fashion. It is used just
    27  // to query the FD's current state.
    28  func NonBlockingPoll(fd int32, mask waiter.EventMask) waiter.EventMask {
    29  	e := struct {
    30  		fd      int32
    31  		events  int16
    32  		revents int16
    33  	}{
    34  		fd:     fd,
    35  		events: int16(mask.ToLinux()),
    36  	}
    37  
    38  	ts := unix.Timespec{
    39  		Sec:  0,
    40  		Nsec: 0,
    41  	}
    42  
    43  	for {
    44  		n, _, err := unix.RawSyscall6(unix.SYS_PPOLL, uintptr(unsafe.Pointer(&e)), 1,
    45  			uintptr(unsafe.Pointer(&ts)), 0, 0, 0)
    46  		// Interrupted by signal, try again.
    47  		if err == unix.EINTR {
    48  			continue
    49  		}
    50  		// If an error occur we'll conservatively say the FD is ready for
    51  		// whatever is being checked.
    52  		if err != 0 {
    53  			return mask
    54  		}
    55  
    56  		// If no FDs were returned, it wasn't ready for anything.
    57  		if n == 0 {
    58  			return 0
    59  		}
    60  
    61  		// Otherwise we got the ready events in the revents field.
    62  		return waiter.EventMaskFromLinux(uint32(e.revents))
    63  	}
    64  }
    65  
    66  // epollWait performs a blocking wait on epfd.
    67  //
    68  // Preconditions: len(events) > 0
    69  func epollWait(epfd int, events []unix.EpollEvent, msec int) (int, error) {
    70  	if len(events) == 0 {
    71  		panic("Empty events passed to EpollWait")
    72  	}
    73  
    74  	// We actually use epoll_pwait with NULL sigmask instead of epoll_wait
    75  	// since that is what the Go >= 1.11 runtime prefers.
    76  	r, _, e := unix.Syscall6(unix.SYS_EPOLL_PWAIT, uintptr(epfd), uintptr(unsafe.Pointer(&events[0])), uintptr(len(events)), uintptr(msec), 0, 0)
    77  	if e != 0 {
    78  		return 0, e
    79  	}
    80  	return int(r), nil
    81  }