fsx: Remove environment references

This commit removes the reference to the environment from the fsx
package.

pkg/fsx/fsx.go

@@ -1,16 +1,37 @@
 // Package fsx provides additional file system functionality.
 //
-// Several functions in this package provide umask-ignoring functions.
-// Using these functions intervenes with the global umask.
-//
-// It is not safe to use functions provided by the standard go library concurrently with this function.
+// All functions in this package ignore the umask.
+// As such it is not safe to use otherwise equivalent functions provided by the standard go library concurrently with this package.
 // Users should take care that no other code in their application uses these functions.
 package fsx
 
-import "io/fs"
+import (
+	"io/fs"
+	"sync"
+	"syscall"
+)
 
 // DefaultFilePerm should be used by callers to use a consistent file mode for new files.
 const DefaultFilePerm fs.FileMode = 0666
 
-// DefaultDirPerm should be used by callers to use a consistent mode for new directories.
-const DefaultDirPerm fs.FileMode = fs.ModeDir | fs.ModePerm
+// mask is the global mask lock
+var m mask
+
+// mask allows disabling and re-enabling the global umask.
+// it is used by allow functions of this package.
+type mask struct {
+	l     sync.Mutex // locked?
+	umask int        // previous mask
+}
+
+// Lock blocks until no other function is using this umask
+// and then sets it to 0.
+func (mask *mask) Lock() {
+	mask.l.Lock()
+	mask.umask = syscall.Umask(0)
+}
+
+func (mask *mask) Unlock() {
+	mask.umask = syscall.Umask(mask.umask)
+	mask.l.Unlock()
+}