github.com/oweisse/u-root@v0.0.0-20181109060735-d005ad25fef1/pkg/loop/losetup_linux.go (about)

     1  // Copyright 2018 the u-root Authors. All rights reserved
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package loop
     6  
     7  import (
     8  	"fmt"
     9  	"os"
    10  	"syscall"
    11  )
    12  
    13  const (
    14  	/*
    15  	 * IOCTL commands --- we will commandeer 0x4C ('L')
    16  	 */
    17  	LOOP_SET_CAPACITY = 0x4C07
    18  	LOOP_CHANGE_FD    = 0x4C06
    19  	LOOP_GET_STATUS64 = 0x4C05
    20  	LOOP_SET_STATUS64 = 0x4C04
    21  	LOOP_GET_STATUS   = 0x4C03
    22  	LOOP_SET_STATUS   = 0x4C02
    23  	LOOP_CLR_FD       = 0x4C01
    24  	LOOP_SET_FD       = 0x4C00
    25  	LO_NAME_SIZE      = 64
    26  	LO_KEY_SIZE       = 32
    27  	/* /dev/loop-control interface */
    28  	LOOP_CTL_ADD      = 0x4C80
    29  	LOOP_CTL_REMOVE   = 0x4C81
    30  	LOOP_CTL_GET_FREE = 0x4C82
    31  )
    32  
    33  // FindDevice finds an unused loop device.
    34  func FindDevice() (name string, err error) {
    35  	cfd, err := os.OpenFile("/dev/loop-control", os.O_RDWR, 0644)
    36  	if err != nil {
    37  		return "", err
    38  	}
    39  	defer cfd.Close()
    40  
    41  	number, err := CtlGetFree(cfd.Fd())
    42  	if err != nil {
    43  		return "", err
    44  	}
    45  	return fmt.Sprintf("/dev/loop%d", number), nil
    46  }
    47  
    48  // ClearFd clears the loop device associated with filedescriptor fd.
    49  func ClearFd(fd uintptr) error {
    50  	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, fd, LOOP_CLR_FD, 0); err != 0 {
    51  		return err
    52  	}
    53  
    54  	return nil
    55  }
    56  
    57  // CtlGetFree finds a free loop device querying the loop control device pointed
    58  // by fd. It returns the number of the free loop device /dev/loopX
    59  func CtlGetFree(fd uintptr) (uintptr, error) {
    60  	number, _, err := syscall.Syscall(syscall.SYS_IOCTL, fd, LOOP_CTL_GET_FREE, 0)
    61  	if err != 0 {
    62  		return 0, err
    63  	}
    64  	return number, nil
    65  }
    66  
    67  // SetFd associates a loop device pointed by lfd with a regular file pointed by ffd.
    68  func SetFd(lfd, ffd uintptr) error {
    69  	_, _, err := syscall.Syscall(syscall.SYS_IOCTL, lfd, LOOP_SET_FD, ffd)
    70  	if err != 0 {
    71  		return err
    72  	}
    73  
    74  	return nil
    75  }
    76  
    77  // SetFdFiles associates loop device "devicename" with regular file "filename"
    78  func SetFdFiles(devicename, filename string) error {
    79  	mode := os.O_RDWR
    80  	file, err := os.OpenFile(filename, mode, 0644)
    81  	if err != nil {
    82  		mode = os.O_RDONLY
    83  		file, err = os.OpenFile(filename, mode, 0644)
    84  		if err != nil {
    85  			return err
    86  		}
    87  	}
    88  	defer file.Close()
    89  
    90  	device, err := os.OpenFile(devicename, mode, 0644)
    91  	if err != nil {
    92  		return err
    93  	}
    94  	defer device.Close()
    95  
    96  	return SetFd(device.Fd(), file.Fd())
    97  }
    98  
    99  // ClearFdFile clears the loop device "devicename"
   100  func ClearFdFile(devicename string) error {
   101  	device, err := os.Open(devicename)
   102  	if err != nil {
   103  		return err
   104  	}
   105  	defer device.Close()
   106  
   107  	return ClearFd(device.Fd())
   108  }