Use LOOP_CONFIGURE when creating loop devices

alex-matei · austinvazquez · commit a0739dc0e800 · 2024-05-13T15:19:25.000Z
LOOP_CONFIGURE is a new ioctl that is a lot faster than the LOOP_SET_FD+LOOP_SET_STATUS64 calls Signed-off-by: Alexandru Matei <alexandru.matei@uipath.com> (cherry picked from commit a782fd6) Signed-off-by: Austin Vazquez <macedonv@amazon.com>
diff --git a/mount/losetup_linux.go b/mount/losetup_linux.go
@@ -21,8 +21,11 @@ import (
 	"fmt"
 	"os"
 	"strings"
+	"syscall"
 	"time"
+	"unsafe"
 
+	kernel "github.com/containerd/containerd/contrib/seccomp/kernelversion"
 	"github.com/containerd/containerd/pkg/randutil"
 	"golang.org/x/sys/unix"
 )
@@ -32,8 +35,26 @@ const (
 	loopDevFormat   = "/dev/loop%d"
 
 	ebusyString = "device or resource busy"
+
+	loopConfigureIoctl = 0x4c0a
 )
 
+type LoopConfig struct {
+	Fd        uint32
+	BlockSize uint32
+	Info      unix.LoopInfo64
+	Reserved  [8]uint64
+}
+
+func ioctlConfigure(fd int, value *LoopConfig) error {
+	_, _, err := syscall.Syscall(syscall.SYS_IOCTL, uintptr(fd), uintptr(loopConfigureIoctl), uintptr(unsafe.Pointer(value)))
+	if err == 0 {
+		return nil
+	}
+
+	return err
+}
+
 // LoopParams parameters to control loop device setup
 type LoopParams struct {
 	// Loop device should forbid write
@@ -84,6 +105,32 @@ func setupLoopDev(backingFile, loopDev string, param LoopParams) (_ *os.File, re
 		}
 	}()
 
+	fiveDotEight := kernel.KernelVersion{Kernel: 5, Major: 8}
+	if ok, err := kernel.GreaterEqualThan(fiveDotEight); err == nil && ok {
+		config := LoopConfig{
+			Fd: uint32(back.Fd()),
+		}
+
+		copy(config.Info.File_name[:], backingFile)
+		if param.Readonly {
+			config.Info.Flags |= unix.LO_FLAGS_READ_ONLY
+		}
+
+		if param.Autoclear {
+			config.Info.Flags |= unix.LO_FLAGS_AUTOCLEAR
+		}
+
+		if param.Direct {
+			config.Info.Flags |= unix.LO_FLAGS_DIRECT_IO
+		}
+
+		if err := ioctlConfigure(int(loop.Fd()), &config); err != nil {
+			return nil, fmt.Errorf("failed to configure loop device: %s: %w", loopDev, err)
+		}
+
+		return loop, nil
+	}
+
 	// 2. Set FD
 	if err := unix.IoctlSetInt(int(loop.Fd()), unix.LOOP_SET_FD, int(back.Fd())); err != nil {
 		return nil, fmt.Errorf("could not set loop fd for device: %s: %w", loopDev, err)
