github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/fs/host/util_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  package host
    16  
    17  import (
    18  	"unsafe"
    19  
    20  	"golang.org/x/sys/unix"
    21  	"github.com/SagerNet/gvisor/pkg/abi/linux"
    22  	"github.com/SagerNet/gvisor/pkg/sentry/fs"
    23  	ktime "github.com/SagerNet/gvisor/pkg/sentry/kernel/time"
    24  )
    25  
    26  // NulByte is a single NUL byte. It is passed to readlinkat as an empty string.
    27  var NulByte byte = '\x00'
    28  
    29  func readLink(fd int) (string, error) {
    30  	// Buffer sizing copied from os.Readlink.
    31  	for l := 128; ; l *= 2 {
    32  		b := make([]byte, l)
    33  		n, _, errno := unix.Syscall6(
    34  			unix.SYS_READLINKAT,
    35  			uintptr(fd),
    36  			uintptr(unsafe.Pointer(&NulByte)), // ""
    37  			uintptr(unsafe.Pointer(&b[0])),
    38  			uintptr(l),
    39  			0, 0)
    40  		if errno != 0 {
    41  			return "", errno
    42  		}
    43  		if n < uintptr(l) {
    44  			return string(b[:n]), nil
    45  		}
    46  	}
    47  }
    48  
    49  func timespecFromTimestamp(t ktime.Time, omit, setSysTime bool) unix.Timespec {
    50  	if omit {
    51  		return unix.Timespec{0, linux.UTIME_OMIT}
    52  	}
    53  	if setSysTime {
    54  		return unix.Timespec{0, linux.UTIME_NOW}
    55  	}
    56  	return unix.NsecToTimespec(t.Nanoseconds())
    57  }
    58  
    59  func setTimestamps(fd int, ts fs.TimeSpec) error {
    60  	if ts.ATimeOmit && ts.MTimeOmit {
    61  		return nil
    62  	}
    63  	var sts [2]unix.Timespec
    64  	sts[0] = timespecFromTimestamp(ts.ATime, ts.ATimeOmit, ts.ATimeSetSystemTime)
    65  	sts[1] = timespecFromTimestamp(ts.MTime, ts.MTimeOmit, ts.MTimeSetSystemTime)
    66  	_, _, errno := unix.Syscall6(
    67  		unix.SYS_UTIMENSAT,
    68  		uintptr(fd),
    69  		0, /* path */
    70  		uintptr(unsafe.Pointer(&sts)),
    71  		0, /* flags */
    72  		0, 0)
    73  	if errno != 0 {
    74  		return errno
    75  	}
    76  	return nil
    77  }