github.com/ttpreport/gvisor-ligolo@v0.0.0-20240123134145-a858404967ba/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  //go:build linux
    16  // +build linux
    17  
    18  package fdnotifier
    19  
    20  import (
    21  	"unsafe"
    22  
    23  	"github.com/ttpreport/gvisor-ligolo/pkg/waiter"
    24  	"golang.org/x/sys/unix"
    25  )
    26  
    27  // NonBlockingPoll polls the given FD in non-blocking fashion. It is used just
    28  // to query the FD's current state.
    29  func NonBlockingPoll(fd int32, mask waiter.EventMask) waiter.EventMask {
    30  	e := struct {
    31  		fd      int32
    32  		events  int16
    33  		revents int16
    34  	}{
    35  		fd:     fd,
    36  		events: int16(mask.ToLinux()),
    37  	}
    38  
    39  	ts := unix.Timespec{
    40  		Sec:  0,
    41  		Nsec: 0,
    42  	}
    43  
    44  	for {
    45  		n, _, err := unix.RawSyscall6(unix.SYS_PPOLL, uintptr(unsafe.Pointer(&e)), 1,
    46  			uintptr(unsafe.Pointer(&ts)), 0, 0, 0)
    47  		// Interrupted by signal, try again.
    48  		if err == unix.EINTR {
    49  			continue
    50  		}
    51  		// If an error occur we'll conservatively say the FD is ready for
    52  		// whatever is being checked.
    53  		if err != 0 {
    54  			return mask
    55  		}
    56  
    57  		// If no FDs were returned, it wasn't ready for anything.
    58  		if n == 0 {
    59  			return 0
    60  		}
    61  
    62  		// Otherwise we got the ready events in the revents field.
    63  		return waiter.EventMaskFromLinux(uint32(e.revents))
    64  	}
    65  }
    66  
    67  // epollWait performs a blocking wait on epfd.
    68  //
    69  // Preconditions: len(events) > 0
    70  func epollWait(epfd int, events []unix.EpollEvent, msec int) (int, error) {
    71  	if len(events) == 0 {
    72  		panic("Empty events passed to EpollWait")
    73  	}
    74  
    75  	// We actually use epoll_pwait with NULL sigmask instead of epoll_wait
    76  	// since that is what the Go >= 1.11 runtime prefers.
    77  	r, _, e := unix.Syscall6(unix.SYS_EPOLL_PWAIT, uintptr(epfd), uintptr(unsafe.Pointer(&events[0])), uintptr(len(events)), uintptr(msec), 0, 0)
    78  	if e != 0 {
    79  		return 0, e
    80  	}
    81  	return int(r), nil
    82  }