Allows to open disk from already existing os.File descriptor

I.e. in some fs.FS compliant VFS, given that vfs.Open("some.img") returns fs.File

Author: aol-nnov

diskfs.go

@@ -105,6 +105,7 @@ package diskfs
 import (
 	"errors"
 	"fmt"
+	"io/fs"
 	"os"
 
 	log "github.com/sirupsen/logrus"
@@ -332,6 +333,29 @@ func Open(device string, opts ...OpenOpt) (*disk.Disk, error) {
 	return initDisk(f, ReadWriteExclusive, opt.sectorSize)
 }
 
+// Open a Disk using provided fs.File to a device in read-only mode
+// Use OpenOpt to control options, such as sector size or open mode.
+func OpenFile(f fs.File, opts ...OpenOpt) (*disk.Disk, error) {
+
+	opt := &openOpts{
+		mode:       ReadOnly,
+		sectorSize: SectorSizeDefault,
+	}
+
+	for _, o := range opts {
+		if err := o(opt); err != nil {
+			return nil, err
+		}
+	}
+
+	if osFile, ok := f.(*os.File); ok {
+		return initDisk(osFile, opt.mode, opt.sectorSize)
+	}
+
+	fi, _ := f.Stat()
+	return nil, fmt.Errorf("could not open device image %s with mode %v", fi.Name(), opt.mode)
+}
+
 // Create a Disk from a path to a device
 // Should pass a path to a block device e.g. /dev/sda or a path to a file /tmp/foo.img
 // The provided device must not exist at the time you call Create()