Refactor attach loop device in pure Go

graphdriver/devmapper/deviceset.go

@@ -383,7 +383,7 @@ func (devices *DeviceSet) ResizePool(size int64) error {
 		return fmt.Errorf("Can't shrink file")
 	}
 
-	dataloopback := FindLoopDeviceFor(&osFile{File: datafile})
+	dataloopback := FindLoopDeviceFor(datafile)
 	if dataloopback == nil {
 		return fmt.Errorf("Unable to find loopback mount for: %s", datafilename)
 	}
@@ -395,7 +395,7 @@ func (devices *DeviceSet) ResizePool(size int64) error {
 	}
 	defer metadatafile.Close()
 
-	metadataloopback := FindLoopDeviceFor(&osFile{File: metadatafile})
+	metadataloopback := FindLoopDeviceFor(metadatafile)
 	if metadataloopback == nil {
 		return fmt.Errorf("Unable to find loopback mount for: %s", metadatafilename)
 	}
@@ -491,14 +491,14 @@ func (devices *DeviceSet) initDevmapper(doInit bool) error {
 	if info.Exists == 0 {
 		utils.Debugf("Pool doesn't exist. Creating it.")
 
-		dataFile, err := AttachLoopDevice(data)
+		dataFile, err := attachLoopDevice(data)
 		if err != nil {
 			utils.Debugf("\n--->Err: %s\n", err)
 			return err
 		}
 		defer dataFile.Close()
 
-		metadataFile, err := AttachLoopDevice(metadata)
+		metadataFile, err := attachLoopDevice(metadata)
 		if err != nil {
 			utils.Debugf("\n--->Err: %s\n", err)
 			return err
@@ -637,7 +637,7 @@ func (devices *DeviceSet) deactivateDevice(hash string) error {
 // or b) the 1 second timeout expires.
 func (devices *DeviceSet) waitRemove(hash string) error {
 	utils.Debugf("[deviceset %s] waitRemove(%s)", devices.devicePrefix, hash)
-	defer utils.Debugf("[deviceset %s] waitRemove END", devices.devicePrefix, hash)
+	defer utils.Debugf("[deviceset %s] waitRemove(%) END", devices.devicePrefix, hash)
 	devname, err := devices.byHash(hash)
 	if err != nil {
 		return err

graphdriver/devmapper/devmapper.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"github.com/dotcloud/docker/utils"
 	"runtime"
+	"unsafe"
 )
 
 type DevmapperLogger interface {
@@ -177,15 +178,6 @@ func (t *Task) GetNextTarget(next uintptr) (nextPtr uintptr, start uint64,
 		start, length, targetType, params
 }
 
-func AttachLoopDevice(filename string) (*osFile, error) {
-	var fd int
-	res := DmAttachLoopDevice(filename, &fd)
-	if res == "" {
-		return nil, ErrAttachLoopbackDevice
-	}
-	return &osFile{File: osNewFile(uintptr(fd), res)}, nil
-}
-
 func getLoopbackBackingFile(file *osFile) (uint64, uint64, error) {
 	dev, inode, err := DmGetLoopbackBackingFile(file.Fd())
 	if err != 0 {
@@ -223,11 +215,10 @@ func FindLoopDeviceFor(file *osFile) *osFile {
 			continue
 		}
 
-		dev, inode, err := getLoopbackBackingFile(&osFile{File: file})
+		dev, inode, err := getLoopbackBackingFile(file)
 		if err == nil && dev == targetDevice && inode == targetInode {
-			return &osFile{File: file}
+			return file
 		}
-
 		file.Close()
 	}
 
@@ -420,7 +411,7 @@ func suspendDevice(name string) error {
 		return err
 	}
 	if err := task.Run(); err != nil {
-		return fmt.Errorf("Error running DeviceSuspend")
+		return fmt.Errorf("Error running DeviceSuspend: %s", err)
 	}
 	return nil
 }
@@ -437,7 +428,7 @@ func resumeDevice(name string) error {
 	}
 
 	if err := task.Run(); err != nil {
-		return fmt.Errorf("Error running DeviceSuspend")
+		return fmt.Errorf("Error running DeviceResume")
 	}
 
 	UdevWait(cookie)
@@ -574,3 +565,109 @@ func (devices *DeviceSet) createSnapDevice(poolName string, deviceId int, baseNa
 
 	return nil
 }
+
+type LoopInfo64 struct {
+	loDevice           uint64 /* ioctl r/o */
+	loInode            uint64 /* ioctl r/o */
+	loRdevice          uint64 /* ioctl r/o */
+	loOffset           uint64
+	loSizelimit        uint64 /* bytes, 0 == max available */
+	loNumber           uint32 /* ioctl r/o */
+	loEncrypt_type     uint32
+	loEncrypt_key_size uint32 /* ioctl w/o */
+	loFlags            uint32 /* ioctl r/o */
+	loFileName         [LoNameSize]uint8
+	loCryptName        [LoNameSize]uint8
+	loEncryptKey       [LoKeySize]uint8 /* ioctl w/o */
+	loInit             [2]uint64
+}
+
+// attachLoopDevice attaches the given sparse file to the next
+// available loopback device. It returns an opened *osFile.
+func attachLoopDevice(filename string) (loop *osFile, err error) {
+	startIndex := 0
+
+	// Try to retrieve the next available loopback device via syscall.
+	// If it fails, we discard error and start loopking for a
+	// loopback from index 0.
+	if f, err := osOpenFile("/dev/loop-control", osORdOnly, 0644); err == nil {
+		if index, _, err := sysSyscall(sysSysIoctl, f.Fd(), LoopCtlGetFree, 0); err != 0 {
+			utils.Debugf("Error retrieving the next available loopback: %s", err)
+		} else if index > 0 {
+			startIndex = int(index)
+		}
+		f.Close()
+	}
+
+	// Open the given sparse file (use OpenFile because Open sets O_CLOEXEC)
+	f, err := osOpenFile(filename, osORdWr, 0644)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var (
+		target   string
+		loopFile *osFile
+	)
+	// Start looking for a free /dev/loop
+	for i := startIndex; ; {
+		target = fmt.Sprintf("/dev/loop%d", i)
+
+		fi, err := osStat(target)
+		if err != nil {
+			if osIsNotExist(err) {
+				utils.Errorf("There are no more loopback device available.")
+			}
+		}
+
+		// FIXME: Check here if target is a block device (in C: S_ISBLK(mode))
+		if fi.IsDir() {
+		}
+
+		// Open the targeted loopback (use OpenFile because Open sets O_CLOEXEC)
+		loopFile, err = osOpenFile(target, osORdWr, 0644)
+		if err != nil {
+			return nil, err
+		}
+
+		// Try to attach to the loop file
+		if _, _, err := sysSyscall(sysSysIoctl, loopFile.Fd(), LoopSetFd, f.Fd()); err != 0 {
+			loopFile.Close()
+			// If the error is EBUSY, then try the next loopback
+			if err != sysEBusy {
+				utils.Errorf("Cannot set up loopback device %s: %s", target, err)
+				return nil, err
+			}
+		} else {
+			// In case of success, we finished. Break the loop.
+			break
+		}
+		// In case of EBUSY error, the loop keep going.
+	}
+
+	// This can't happen, but let's be sure
+	if loopFile == nil {
+		return nil, fmt.Errorf("Unreachable code reached! Error attaching %s to a loopback device.", filename)
+	}
+
+	// Set the status of the loopback device
+	var loopInfo LoopInfo64
+
+	// Due to type incompatibility (string vs [64]uint8), we copy data
+	copy(loopInfo.loFileName[:], target[:])
+	loopInfo.loOffset = 0
+	loopInfo.loFlags = LoFlagsAutoClear
+
+	if _, _, err := sysSyscall(sysSysIoctl, loopFile.Fd(), LoopSetStatus64, uintptr(unsafe.Pointer(&loopInfo))); err != 0 {
+		// If the call failed, then free the loopback device
+		utils.Errorf("Cannot set up loopback device info: %s", err)
+		if _, _, err := sysSyscall(sysSysIoctl, loopFile.Fd(), LoopClrFd, 0); err != 0 {
+			utils.Errorf("Error while cleaning up the loopback device")
+		}
+		loopFile.Close()
+		return nil, err
+	}
+
+	return loopFile, nil
+}

graphdriver/devmapper/devmapper_wrapper.go

@@ -2,124 +2,14 @@ package devmapper
 
 /*
 #cgo LDFLAGS: -L. -ldevmapper
-#include <stdio.h>
-#include <stdlib.h>
-#include <unistd.h>
 #include <libdevmapper.h>
-#include <linux/loop.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <fcntl.h>
-#include <sys/ioctl.h>
-#include <linux/fs.h>
-#include <errno.h>
-
-#ifndef LOOP_CTL_GET_FREE
-#define LOOP_CTL_GET_FREE       0x4C82
-#endif
-
-// FIXME: this could easily be rewritten in go
-char*			attach_loop_device(const char *filename, int *loop_fd_out)
-{
-  struct loop_info64	loopinfo = {0};
-  struct stat		st;
-  char			buf[64];
-  int			i, loop_fd, fd, start_index;
-  char*			loopname;
-
-
-  *loop_fd_out = -1;
-
-  start_index = 0;
-  fd = open("/dev/loop-control", O_RDONLY);
-  if (fd >= 0) {
-    start_index = ioctl(fd, LOOP_CTL_GET_FREE);
-    close(fd);
-
-    if (start_index < 0)
-      start_index = 0;
-  }
-
-  fd = open(filename, O_RDWR);
-  if (fd < 0) {
-    perror("open");
-    return NULL;
-  }
-
-  loop_fd = -1;
-  for (i = start_index ; loop_fd < 0 ; i++ ) {
-    if (sprintf(buf, "/dev/loop%d", i) < 0) {
-	close(fd);
-	return NULL;
-    }
-
-    if (stat(buf, &st)) {
-      if (!S_ISBLK(st.st_mode)) {
-	 fprintf(stderr, "[error] Loopback device %s is not a block device.\n", buf);
-      } else if (errno == ENOENT) {
-	fprintf(stderr, "[error] There are no more loopback device available.\n");
-      } else {
-	fprintf(stderr, "[error] Unkown error trying to stat the loopback device %s (errno: %d).\n", buf, errno);
-      }
-      close(fd);
-      return NULL;
-    }
-
-    loop_fd = open(buf, O_RDWR);
-    if (loop_fd < 0 && errno == ENOENT) {
-      fprintf(stderr, "[error] The loopback device %s does not exists.\n", buf);
-      close(fd);
-      return NULL;
-    } else if (loop_fd < 0) {
-	fprintf(stderr, "[error] Unkown error openning the loopback device %s. (errno: %d)\n", buf, errno);
-	continue;
-    }
-
-    if (ioctl(loop_fd, LOOP_SET_FD, (void *)(size_t)fd) < 0) {
-      int errsv = errno;
-      close(loop_fd);
-      loop_fd = -1;
-      if (errsv != EBUSY) {
-        close(fd);
-        fprintf(stderr, "cannot set up loopback device %s: %s", buf, strerror(errsv));
-        return NULL;
-      }
-      continue;
-    }
-
-    close(fd);
-
-    strncpy((char*)loopinfo.lo_file_name, buf, LO_NAME_SIZE);
-    loopinfo.lo_offset = 0;
-    loopinfo.lo_flags = LO_FLAGS_AUTOCLEAR;
-
-    if (ioctl(loop_fd, LOOP_SET_STATUS64, &loopinfo) < 0) {
-      perror("ioctl LOOP_SET_STATUS64");
-      if (ioctl(loop_fd, LOOP_CLR_FD, 0) < 0) {
-        perror("ioctl LOOP_CLR_FD");
-      }
-      close(loop_fd);
-      fprintf (stderr, "cannot set up loopback device info");
-      return (NULL);
-    }
-
-    loopname = strdup(buf);
-    if (loopname == NULL) {
-      close(loop_fd);
-      return (NULL);
-    }
-
-    *loop_fd_out = loop_fd;
-    return (loopname);
-  }
-
-  return (NULL);
-}
+#include <linux/loop.h> // FIXME: present only for defines, maybe we can remove it?
+#include <linux/fs.h>   // FIXME: present only for BLKGETSIZE64, maybe we can remove it?
 
+// FIXME: Can't we find a way to do the logging in pure Go?
 extern void DevmapperLogCallback(int level, char *file, int line, int dm_errno_or_class, char *str);
 
-static void	log_cb(int level, const char *file, int line,
-		       int dm_errno_or_class, const char *f, ...)
+static void	log_cb(int level, const char *file, int line, int dm_errno_or_class, const char *f, ...)
 {
   char buffer[256];
   va_list ap;
@@ -135,7 +25,6 @@ static void	log_with_errno_init()
 {
   dm_log_with_errno_init(log_cb);
 }
-
 */
 import "C"
 
@@ -147,6 +36,19 @@ type (
 	CDmTask C.struct_dm_task
 )
 
+// FIXME: Make sure the values are defined in C
+const (
+	LoopSetFd        = C.LOOP_SET_FD
+	LoopCtlGetFree   = C.LOOP_CTL_GET_FREE
+	LoopSetStatus64  = C.LOOP_SET_STATUS64
+	LoopClrFd        = C.LOOP_CLR_FD
+	LoFlagsAutoClear = C.LO_FLAGS_AUTOCLEAR
+	LoFlagsReadOnly  = C.LO_FLAGS_READ_ONLY
+	LoFlagsPartScan  = C.LO_FLAGS_PARTSCAN
+	LoKeySize        = C.LO_KEY_SIZE
+	LoNameSize       = C.LO_NAME_SIZE
+)
+
 var (
 	DmAttachLoopDevice       = dmAttachLoopDeviceFct
 	DmGetBlockSize           = dmGetBlockSizeFct
@@ -185,28 +87,26 @@ func dmTaskCreateFct(taskType int) *CDmTask {
 }
 
 func dmTaskRunFct(task *CDmTask) int {
-	return int(C.dm_task_run((*C.struct_dm_task)(task)))
+	ret, _ := C.dm_task_run((*C.struct_dm_task)(task))
+	return int(ret)
 }
 
 func dmTaskSetNameFct(task *CDmTask, name string) int {
 	Cname := C.CString(name)
 	defer free(Cname)
 
-	return int(C.dm_task_set_name((*C.struct_dm_task)(task),
-		Cname))
+	return int(C.dm_task_set_name((*C.struct_dm_task)(task), Cname))
 }
 
 func dmTaskSetMessageFct(task *CDmTask, message string) int {
 	Cmessage := C.CString(message)
 	defer free(Cmessage)
 
-	return int(C.dm_task_set_message((*C.struct_dm_task)(task),
-		Cmessage))
+	return int(C.dm_task_set_message((*C.struct_dm_task)(task), Cmessage))
 }
 
 func dmTaskSetSectorFct(task *CDmTask, sector uint64) int {
-	return int(C.dm_task_set_sector((*C.struct_dm_task)(task),
-		C.uint64_t(sector)))
+	return int(C.dm_task_set_sector((*C.struct_dm_task)(task), C.uint64_t(sector)))
 }
 
 func dmTaskSetCookieFct(task *CDmTask, cookie *uint, flags uint16) int {
@@ -214,13 +114,11 @@ func dmTaskSetCookieFct(task *CDmTask, cookie *uint, flags uint16) int {
 	defer func() {
 		*cookie = uint(cCookie)
 	}()
-	return int(C.dm_task_set_cookie((*C.struct_dm_task)(task), &cCookie,
-		C.uint16_t(flags)))
+	return int(C.dm_task_set_cookie((*C.struct_dm_task)(task), &cCookie, C.uint16_t(flags)))
 }
 
 func dmTaskSetAddNodeFct(task *CDmTask, addNode AddNodeType) int {
-	return int(C.dm_task_set_add_node((*C.struct_dm_task)(task),
-		C.dm_add_node_t(addNode)))
+	return int(C.dm_task_set_add_node((*C.struct_dm_task)(task), C.dm_add_node_t(addNode)))
 }
 
 func dmTaskSetRoFct(task *CDmTask) int {
@@ -236,14 +134,12 @@ func dmTaskAddTargetFct(task *CDmTask,
 	Cparams := C.CString(params)
 	defer free(Cparams)
 
-	return int(C.dm_task_add_target((*C.struct_dm_task)(task),
-		C.uint64_t(start), C.uint64_t(size), Cttype, Cparams))
+	return int(C.dm_task_add_target((*C.struct_dm_task)(task), C.uint64_t(start), C.uint64_t(size), Cttype, Cparams))
 }
 
 func dmGetLoopbackBackingFileFct(fd uintptr) (uint64, uint64, sysErrno) {
 	var lo64 C.struct_loop_info64
-	_, _, err := sysSyscall(sysSysIoctl, fd, C.LOOP_GET_STATUS64,
-		uintptr(unsafe.Pointer(&lo64)))
+	_, _, err := sysSyscall(sysSysIoctl, fd, C.LOOP_GET_STATUS64, uintptr(unsafe.Pointer(&lo64)))
 	return uint64(lo64.lo_device), uint64(lo64.lo_inode), sysErrno(err)
 }
 
@@ -287,23 +183,23 @@ func dmGetNextTargetFct(task *CDmTask, next uintptr, start, length *uint64, targ
 		*params = C.GoString(Cparams)
 	}()
 
-	nextp := C.dm_get_next_target((*C.struct_dm_task)(task),
-		unsafe.Pointer(next), &Cstart, &Clength, &CtargetType, &Cparams)
+	nextp := C.dm_get_next_target((*C.struct_dm_task)(task), unsafe.Pointer(next), &Cstart, &Clength, &CtargetType, &Cparams)
 	return uintptr(nextp)
 }
 
 func dmAttachLoopDeviceFct(filename string, fd *int) string {
-	cFilename := C.CString(filename)
-	defer free(cFilename)
-
-	var cFd C.int
-	defer func() {
-		*fd = int(cFd)
-	}()
-
-	ret := C.attach_loop_device(cFilename, &cFd)
-	defer free(ret)
-	return C.GoString(ret)
+	return ""
+	// cFilename := C.CString(filename)
+	// defer free(cFilename)
+
+	// var cFd C.int
+	// defer func() {
+	// 	*fd = int(cFd)
+	// }()
+
+	// ret := C.attach_loop_device(cFilename, &cFd)
+	// defer free(ret)
+	// return C.GoString(ret)
 }
 
 func getBlockSizeFct(fd uintptr, size *uint64) sysErrno {

graphdriver/devmapper/sys.go

@@ -19,7 +19,11 @@ var (
 	sysCloseOnExec = syscall.CloseOnExec
 	sysSyscall     = syscall.Syscall
 
-	osOpenFile   = os.OpenFile
+	osOpenFile = func(name string, flag int, perm os.FileMode) (*osFile, error) {
+		f, err := os.OpenFile(name, flag, perm)
+		return &osFile{File: f}, err
+	}
+	osOpen       = func(name string) (*osFile, error) { f, err := os.Open(name); return &osFile{File: f}, err }
 	osNewFile    = os.NewFile
 	osCreate     = os.Create
 	osStat       = os.Stat
@@ -40,7 +44,9 @@ const (
 	sysMsRdOnly = syscall.MS_RDONLY
 	sysEInval   = syscall.EINVAL
 	sysSysIoctl = syscall.SYS_IOCTL
+	sysEBusy    = syscall.EBUSY
 
+	osORdOnly = os.O_RDONLY
 	osORdWr   = os.O_RDWR
 	osOCreate = os.O_CREATE
 )