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Address loop dev PR comments #4178

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Signed-off-by: Maksym Pavlenko <pavlenko.maksym@gmail.com>
This commit is contained in:
Maksym Pavlenko 2021-01-04 10:44:29 -08:00
parent b7026236f4
commit c5fa0298c1
3 changed files with 54 additions and 95 deletions
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134
mount/losetup_linux.go
View File

@ -26,28 +26,17 @@ import (
"unsafe"
"github.com/pkg/errors"
"golang.org/x/sys/unix"
)
const (
loopControlPath = "/dev/loop-control"
loopDevFormat = "/dev/loop%d"
// According to util-linux/include/loopdev.h
ioctlSetFd = 0x4C00
ioctlClrFd = 0x4C01
ioctlSetStatus64 = 0x4C04
ioctlGetFree = 0x4C82
loFlagsReadonly = 1
//loFlagsUseAops = 2
loFlagsAutoclear = 4
//loFlagsPartScan = 8
loFlagsDirectIO = 16
ebusyString = "device or resource busy"
)
// parameters to control loop device setup
// LoopParams parameters to control loop device setup
type LoopParams struct {
// Loop device should forbid write
Readonly bool
@ -58,29 +47,6 @@ type LoopParams struct {
Direct bool
}
// struct loop_info64 in util-linux/include/loopdev.h
type loopInfo struct {
/*
device uint64
inode uint64
rdevice uint64
offset uint64
sizelimit uint64
number uint32
encryptType uint32
encryptKeySize uint32
*/
_ [13]uint32
flags uint32
fileName [64]byte
/*
cryptName [64]byte
encryptKey [32]byte
init [2]uint64
*/
_ [112]byte
}
func ioctl(fd, req, args uintptr) (uintptr, uintptr, error) {
r1, r2, errno := syscall.Syscall(syscall.SYS_IOCTL, fd, req, args)
if errno != 0 {
@ -96,63 +62,70 @@ func getFreeLoopDev() (uint32, error) {
return 0, errors.Errorf("could not open %v: %v", loopControlPath, err)
}
defer ctrl.Close()
num, _, err := ioctl(ctrl.Fd(), ioctlGetFree, 0)
num, _, err := ioctl(ctrl.Fd(), unix.LOOP_CTL_GET_FREE, 0)
if err != nil {
return 0, errors.Wrap(err, "could not get free loop device")
}
return uint32(num), nil
}
func setupLoopDev(backingFile, loopDev string, param LoopParams) (devFile *os.File, err error) {
func setupLoopDev(backingFile, loopDev string, param LoopParams) error {
// 1. Open backing file and loop device
oflags := os.O_RDWR
flags := os.O_RDWR
if param.Readonly {
oflags = os.O_RDONLY
flags = os.O_RDONLY
}
back, err := os.OpenFile(backingFile, oflags, 0)
back, err := os.OpenFile(backingFile, flags, 0)
if err != nil {
return nil, errors.Errorf("could not open backing file: %v", err)
return errors.Wrapf(err, "could not open backing file: %s", backingFile)
}
defer back.Close()
loopFile, err := os.OpenFile(loopDev, oflags, 0)
loop, err := os.OpenFile(loopDev, flags, 0)
if err != nil {
return nil, errors.Errorf("could not open loop device: %v", err)
return errors.Wrapf(err, "could not open loop device: %s", loopDev)
}
defer func() {
if err != nil {
loopFile.Close()
}
}()
defer loop.Close()
// 2. Set FD
if _, _, err = ioctl(loopFile.Fd(), ioctlSetFd, back.Fd()); err != nil {
return nil, errors.Errorf("could not set loop fd: %v", err)
if _, _, err = ioctl(loop.Fd(), unix.LOOP_SET_FD, back.Fd()); err != nil {
return errors.Wrapf(err, "could not set loop fd for device: %s", loopDev)
}
// 3. Set Info
info := loopInfo{}
copy(info.fileName[:], []byte(backingFile))
info := unix.LoopInfo64{}
copy(info.File_name[:], backingFile)
if param.Readonly {
info.flags |= loFlagsReadonly
info.Flags |= unix.LO_FLAGS_READ_ONLY
}
if param.Autoclear {
info.flags |= loFlagsAutoclear
info.Flags |= unix.LO_FLAGS_AUTOCLEAR
}
if param.Direct {
info.flags |= loFlagsAutoclear
info.Flags |= unix.LO_FLAGS_DIRECT_IO
}
if _, _, err := ioctl(loopFile.Fd(), ioctlSetStatus64, uintptr(unsafe.Pointer(&info))); err != nil {
_, _, err = ioctl(loop.Fd(), unix.LOOP_SET_STATUS64, uintptr(unsafe.Pointer(&info)))
if err == nil {
return nil
}
if param.Direct {
// Retry w/o direct IO flag in case kernel does not support it. The downside is that
// it will suffer from double cache problem.
info.flags &= ^(uint32(loFlagsDirectIO))
if _, _, err := ioctl(loopFile.Fd(), ioctlSetStatus64, uintptr(unsafe.Pointer(&info))); err != nil {
ioctl(loopFile.Fd(), ioctlClrFd, 0)
return nil, errors.Errorf("cannot set loop info:%v", err)
info.Flags &= ^(uint32(unix.LO_FLAGS_DIRECT_IO))
_, _, err = ioctl(loop.Fd(), unix.LOOP_SET_STATUS64, uintptr(unsafe.Pointer(&info)))
if err == nil {
return nil
}
}
return loopFile, nil
// Cleanup loop fd and return error
_, _, _ = ioctl(loop.Fd(), unix.LOOP_CLR_FD, 0)
return errors.Errorf("failed to set loop device info: %v", err)
}
// setupLoop looks for (and possibly creates) a free loop device, and
@ -169,18 +142,15 @@ func setupLoopDev(backingFile, loopDev string, param LoopParams) (devFile *os.Fi
// the loop device when done with it.
//
// Upon success, the file handle to the loop device is returned.
func setupLoop(backingFile string, param LoopParams) (*os.File, error) {
var loopDev string
func setupLoop(backingFile string, param LoopParams) (string, error) {
for retry := 1; retry < 200; retry++ {
num, err := getFreeLoopDev()
if err != nil {
return nil, err
return "", err
}
loopDev = fmt.Sprintf(loopDevFormat, num)
loopFile, err := setupLoopDev(backingFile, loopDev, param)
if err != nil {
loopDev := fmt.Sprintf(loopDevFormat, num)
if err := setupLoopDev(backingFile, loopDev, param); err != nil {
// Per util-linux/sys-utils/losetup.c:create_loop(),
// free loop device can race and we end up failing
// with EBUSY when trying to set it up.
@ -189,40 +159,36 @@ func setupLoop(backingFile string, param LoopParams) (*os.File, error) {
time.Sleep(time.Millisecond * time.Duration(rand.Intn(retry*10)))
continue
}
return nil, err
}
return loopFile, nil
return "", err
}
return nil, errors.New("Timeout creating new loopback device")
return loopDev, nil
}
return "", errors.New("timeout creating new loopback device")
}
func removeLoop(loopdev string) error {
dev, err := os.Open(loopdev)
file, err := os.Open(loopdev)
if err != nil {
return err
}
_, _, err = ioctl(dev.Fd(), ioctlClrFd, 0)
dev.Close()
defer file.Close()
_, _, err = ioctl(file.Fd(), unix.LOOP_CLR_FD, 0)
return err
}
// Attach a specified backing file to a loop device
func AttachLoopDevice(backingFile string) (string, error) {
dev, err := setupLoop(backingFile, LoopParams{})
if err != nil {
return "", err
}
dev.Close()
return dev.Name(), nil
return setupLoop(backingFile, LoopParams{})
}
// Detach a loop device
func DetachLoopDevice(devices ...string) error {
for _, dev := range devices {
if err := removeLoop(dev); err != nil {
return err
return errors.Wrapf(err, "failed to remove loop device: %s", dev)
}
}

14
mount/losetup_linux_test.go
View File

@ -53,11 +53,11 @@ func TestSetupLoop(t *testing.T) {
}()
/* RO loop */
f, err = setupLoop(backingFile, LoopParams{Readonly: true, Autoclear: true})
path, err := setupLoop(backingFile, LoopParams{Readonly: true, Autoclear: true})
if err != nil {
t.Fatal(err)
}
ff, err := os.OpenFile(f.Name(), os.O_RDWR, 0)
ff, err := os.OpenFile(path, os.O_RDWR, 0)
if err != nil {
t.Fatal(err)
}
@ -67,16 +67,13 @@ func TestSetupLoop(t *testing.T) {
if err = ff.Close(); err != nil {
t.Fatal(err)
}
if err = f.Close(); err != nil {
t.Fatal(err)
}
/* RW loop */
f, err = setupLoop(backingFile, LoopParams{Autoclear: true})
path, err = setupLoop(backingFile, LoopParams{Autoclear: true})
if err != nil {
t.Fatal(err)
}
ff, err = os.OpenFile(f.Name(), os.O_RDWR, 0)
ff, err = os.OpenFile(path, os.O_RDWR, 0)
if err != nil {
t.Fatal(err)
}
@ -86,9 +83,6 @@ func TestSetupLoop(t *testing.T) {
if err = ff.Close(); err != nil {
t.Fatal(err)
}
if err = f.Close(); err != nil {
t.Fatal(err)
}
}
func TestAttachDetachLoopDevice(t *testing.T) {

3
mount/mount_linux.go
View File

@ -85,9 +85,8 @@ func (m *Mount) Mount(target string) (err error) {
if err != nil {
return err
}
defer devFile.Close()
// Mount the loop device instead
source = devFile.Name()
source = devFile
}
if err := mountAt(chdir, source, target, m.Type, uintptr(oflags), data); err != nil {
return err