github.com/avfs/avfs@v0.33.1-0.20240303173310-c6ba67c33eb7/umask_linux.go (about)

     1  //
     2  //  Copyright 2023 The AVFS authors
     3  //
     4  //  Licensed under the Apache License, Version 2.0 (the "License");
     5  //  you may not use this file except in compliance with the License.
     6  //  You may obtain a copy of the License at
     7  //
     8  //  	http://www.apache.org/licenses/LICENSE-2.0
     9  //
    10  //  Unless required by applicable law or agreed to in writing, software
    11  //  distributed under the License is distributed on an "AS IS" BASIS,
    12  //  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  //  See the License for the specific language governing permissions and
    14  //  limitations under the License.
    15  //
    16  
    17  //go:build linux
    18  
    19  package avfs
    20  
    21  import (
    22  	"io/fs"
    23  	"sync"
    24  	"syscall"
    25  )
    26  
    27  var (
    28  	// umask is the file mode creation mask.
    29  	umask fs.FileMode = initUMask() //nolint:gochecknoglobals // Used by UMask and SetUMask.
    30  
    31  	// umLock lock access to the umask.
    32  	umLock sync.RWMutex //nolint:gochecknoglobals // Used by UMask and SetUMask.
    33  )
    34  
    35  func initUMask() fs.FileMode {
    36  	umLock.Lock()
    37  	defer umLock.Unlock()
    38  
    39  	m := syscall.Umask(0) // read mask.
    40  	syscall.Umask(m)      // restore mask after read.
    41  
    42  	return fs.FileMode(m)
    43  }
    44  
    45  // SetUMask sets the file mode creation mask.
    46  // Umask must be set to 0 using umask(2) system call to be read,
    47  // so its value is cached and protected by a mutex.
    48  func SetUMask(mask fs.FileMode) error {
    49  	umLock.Lock()
    50  	m := int(mask & fs.ModePerm)
    51  	_ = syscall.Umask(m)
    52  	umask = fs.FileMode(m)
    53  	umLock.Unlock()
    54  
    55  	return nil
    56  }
    57  
    58  // UMask returns the file mode creation mask.
    59  func UMask() fs.FileMode {
    60  	umLock.RLock()
    61  	um := umask
    62  	umLock.RUnlock()
    63  
    64  	return um
    65  }