diff --git a/internal/util/mmap.go b/internal/util/mmap.go
index a2067b9..45ca3f9 100644
--- a/internal/util/mmap.go
+++ b/internal/util/mmap.go
@@ -29,7 +29,7 @@ func CanMap(ctx context.Context) bool {
 	return s.mmapState.enabled
 }
 
-func (s *mmapState) new(ctx context.Context, mod api.Module, size uint32) *MappedRegion {
+func (s *mmapState) new(ctx context.Context, mod api.Module, size int32) *MappedRegion {
 	// Find unused region.
 	for _, r := range s.regions {
 		if !r.used && r.size == size {
@@ -65,11 +65,11 @@ func (s *mmapState) new(ctx context.Context, mod api.Module, size uint32) *Mappe
 type MappedRegion struct {
 	addr uintptr
 	Ptr  uint32
-	size uint32
+	size int32
 	used bool
 }
 
-func MapRegion(ctx context.Context, mod api.Module, f *os.File, offset int64, size uint32) (*MappedRegion, error) {
+func MapRegion(ctx context.Context, mod api.Module, f *os.File, offset int64, size int32) (*MappedRegion, error) {
 	s := ctx.Value(moduleKey{}).(*moduleState)
 	r := s.new(ctx, mod, size)
 	err := r.mmap(f, offset)
@@ -98,8 +98,8 @@ func (r *MappedRegion) mmap(f *os.File, offset int64) error {
 	return err
 }
 
+// We need the low level mmap for MAP_FIXED to work.
+// Bind the syscall version hoping that it is more stable.
+
 //go:linkname mmap syscall.mmap
 func mmap(addr, length uintptr, prot, flag, fd int, pos int64) (*byte, error)
-
-//go:linkname munmap syscall.munmap
-func munmap(addr, length uintptr) error
diff --git a/sqlite3/vfs.c b/sqlite3/vfs.c
index d2e79fb..7c397ef 100644
--- a/sqlite3/vfs.c
+++ b/sqlite3/vfs.c
@@ -5,8 +5,8 @@
 #include "include.h"
 #include "sqlite3.h"
 
-int go_localtime(struct tm *, sqlite3_int64);
 int go_vfs_find(const char *zVfsName);
+int go_localtime(struct tm *, sqlite3_int64);
 
 int go_randomness(sqlite3_vfs *, int nByte, char *zOut);
 int go_sleep(sqlite3_vfs *, int microseconds);
diff --git a/util/ioutil/seek.go b/util/ioutil/seek.go
index dc86ea1..6f033e6 100644
--- a/util/ioutil/seek.go
+++ b/util/ioutil/seek.go
@@ -8,8 +8,8 @@ import (
 // SeekingReaderAt implements [io.ReaderAt]
 // through an underlying [io.ReadSeeker].
 type SeekingReaderAt struct {
-	l sync.Mutex
 	r io.ReadSeeker
+	l sync.Mutex
 }
 
 // NewSeekingReaderAt creates a new SeekingReaderAt.
diff --git a/vfs/file.go b/vfs/file.go
index 42d03ed..af804d4 100644
--- a/vfs/file.go
+++ b/vfs/file.go
@@ -1,6 +1,7 @@
 package vfs
 
 import (
+	"context"
 	"errors"
 	"io"
 	"io/fs"
@@ -11,6 +12,7 @@ import (
 	"syscall"
 
 	"github.com/ncruces/go-sqlite3/util/osutil"
+	"github.com/tetratelabs/wazero/api"
 )
 
 type vfsOS struct{}
@@ -125,12 +127,12 @@ func (vfsOS) OpenParams(name string, flags OpenFlag, params url.Values) (File, O
 
 type vfsFile struct {
 	*os.File
+	shm      vfsShm
 	lock     LockLevel
 	readOnly bool
 	keepWAL  bool
 	syncDir  bool
 	psow     bool
-	shm      vfsShm
 }
 
 var (
@@ -213,3 +215,9 @@ func (f *vfsFile) PowersafeOverwrite() bool        { return f.psow }
 func (f *vfsFile) PersistentWAL() bool             { return f.keepWAL }
 func (f *vfsFile) SetPowersafeOverwrite(psow bool) { f.psow = psow }
 func (f *vfsFile) SetPersistentWAL(keepWAL bool)   { f.keepWAL = keepWAL }
+
+type fileShm interface {
+	shmMap(context.Context, api.Module, int32, int32, bool) (uint32, error)
+	shmLock(int32, int32, _ShmFlag) error
+	shmUnmap(bool)
+}
diff --git a/vfs/os_bsd.go b/vfs/os_bsd.go
index 3506ec9..f2b5527 100644
--- a/vfs/os_bsd.go
+++ b/vfs/os_bsd.go
@@ -31,15 +31,3 @@ func osReadLock(file *os.File, _ /*start*/, _ /*len*/ int64, _ /*timeout*/ time.
 func osWriteLock(file *os.File, _ /*start*/, _ /*len*/ int64, _ /*timeout*/ time.Duration) _ErrorCode {
 	return osLock(file, unix.LOCK_EX|unix.LOCK_NB, _IOERR_LOCK)
 }
-
-func osGetLock(file *os.File, start, len int64) (int16, _ErrorCode) {
-	lock := unix.Flock_t{
-		Type:  unix.F_WRLCK,
-		Start: start,
-		Len:   len,
-	}
-	if unix.FcntlFlock(file.Fd(), unix.F_GETLK, &lock) != nil {
-		return 0, _IOERR_CHECKRESERVEDLOCK
-	}
-	return lock.Type, _OK
-}
diff --git a/vfs/os_darwin.go b/vfs/os_darwin.go
index 4269445..9826eb2 100644
--- a/vfs/os_darwin.go
+++ b/vfs/os_darwin.go
@@ -14,7 +14,6 @@ const (
 	// https://github.com/apple/darwin-xnu/blob/main/bsd/sys/fcntl.h
 	_F_OFD_SETLK         = 90
 	_F_OFD_SETLKW        = 91
-	_F_OFD_GETLK         = 92
 	_F_OFD_SETLKWTIMEOUT = 93
 )
 
@@ -94,15 +93,3 @@ func osReadLock(file *os.File, start, len int64, timeout time.Duration) _ErrorCo
 func osWriteLock(file *os.File, start, len int64, timeout time.Duration) _ErrorCode {
 	return osLock(file, unix.F_WRLCK, start, len, timeout, _IOERR_LOCK)
 }
-
-func osGetLock(file *os.File, start, len int64) (int16, _ErrorCode) {
-	lock := unix.Flock_t{
-		Type:  unix.F_WRLCK,
-		Start: start,
-		Len:   len,
-	}
-	if unix.FcntlFlock(file.Fd(), _F_OFD_GETLK, &lock) != nil {
-		return 0, _IOERR_CHECKRESERVEDLOCK
-	}
-	return lock.Type, _OK
-}
diff --git a/vfs/os_ofd.go b/vfs/os_ofd.go
index f94ece4..f6898ed 100644
--- a/vfs/os_ofd.go
+++ b/vfs/os_ofd.go
@@ -40,7 +40,7 @@ func osLock(file *os.File, typ int16, start, len int64, timeout time.Duration, d
 			if errno, _ := err.(unix.Errno); errno != unix.EAGAIN {
 				break
 			}
-			if timeout <= 0 || timeout < time.Since(before) {
+			if timeout < time.Since(before) {
 				break
 			}
 			osSleep(time.Millisecond)
@@ -56,15 +56,3 @@ func osReadLock(file *os.File, start, len int64, timeout time.Duration) _ErrorCo
 func osWriteLock(file *os.File, start, len int64, timeout time.Duration) _ErrorCode {
 	return osLock(file, unix.F_WRLCK, start, len, timeout, _IOERR_LOCK)
 }
-
-func osGetLock(file *os.File, start, len int64) (int16, _ErrorCode) {
-	lock := unix.Flock_t{
-		Type:  unix.F_WRLCK,
-		Start: start,
-		Len:   len,
-	}
-	if unix.FcntlFlock(file.Fd(), unix.F_OFD_GETLK, &lock) != nil {
-		return 0, _IOERR_CHECKRESERVEDLOCK
-	}
-	return lock.Type, _OK
-}
diff --git a/vfs/os_unix_lock.go b/vfs/os_unix_lock.go
index fc4309d..cdefa21 100644
--- a/vfs/os_unix_lock.go
+++ b/vfs/os_unix_lock.go
@@ -68,6 +68,18 @@ func osCheckReservedLock(file *os.File) (bool, _ErrorCode) {
 	return lock == unix.F_WRLCK, rc
 }
 
+func osGetLock(file *os.File, start, len int64) (int16, _ErrorCode) {
+	lock := unix.Flock_t{
+		Type:  unix.F_WRLCK,
+		Start: start,
+		Len:   len,
+	}
+	if unix.FcntlFlock(file.Fd(), unix.F_GETLK, &lock) != nil {
+		return 0, _IOERR_CHECKRESERVEDLOCK
+	}
+	return lock.Type, _OK
+}
+
 func osLockErrorCode(err error, def _ErrorCode) _ErrorCode {
 	if err == nil {
 		return _OK
diff --git a/vfs/os_windows.go b/vfs/os_windows.go
index 0fee2f1..99c91f6 100644
--- a/vfs/os_windows.go
+++ b/vfs/os_windows.go
@@ -132,7 +132,7 @@ func osLock(file *os.File, flags, start, len uint32, timeout time.Duration, def
 			if errno, _ := err.(windows.Errno); errno != windows.ERROR_LOCK_VIOLATION {
 				break
 			}
-			if timeout <= 0 || timeout < time.Since(before) {
+			if timeout < time.Since(before) {
 				break
 			}
 			osSleep(time.Millisecond)
diff --git a/vfs/shm.go b/vfs/shm.go
index 1dda1b5..42da5b9 100644
--- a/vfs/shm.go
+++ b/vfs/shm.go
@@ -33,7 +33,7 @@ const (
 	_SHM_DMS   = _SHM_BASE + _SHM_NLOCK
 )
 
-func (f *vfsFile) shmMap(ctx context.Context, mod api.Module, id, size uint32, extend bool) (uint32, error) {
+func (f *vfsFile) shmMap(ctx context.Context, mod api.Module, id, size int32, extend bool) (uint32, error) {
 	// Ensure size is a multiple of the OS page size.
 	if int(size)&(unix.Getpagesize()-1) != 0 {
 		return 0, _IOERR_SHMMAP
@@ -96,9 +96,9 @@ func (f *vfsFile) shmMap(ctx context.Context, mod api.Module, id, size uint32, e
 	return r.Ptr, nil
 }
 
-func (f *vfsFile) shmLock(offset, n uint32, flags _ShmFlag) error {
+func (f *vfsFile) shmLock(offset, n int32, flags _ShmFlag) error {
 	// Argument check.
-	if n == 0 || offset+n > _SHM_NLOCK {
+	if n <= 0 || offset < 0 || offset+n > _SHM_NLOCK {
 		panic(util.AssertErr())
 	}
 	switch flags {
diff --git a/vfs/tests/speedtest1/speedtest1_test.go b/vfs/tests/speedtest1/speedtest1_test.go
index 786d6b9..e050e5d 100644
--- a/vfs/tests/speedtest1/speedtest1_test.go
+++ b/vfs/tests/speedtest1/speedtest1_test.go
@@ -84,7 +84,7 @@ func initFlags() {
 
 func Benchmark_speedtest1(b *testing.B) {
 	output.Reset()
-	ctx := util.NewContext(context.Background(), false)
+	ctx := util.NewContext(context.Background(), true)
 	name := filepath.Join(b.TempDir(), "test.db")
 	args := append(options, "--size", strconv.Itoa(b.N), name)
 	cfg := wazero.NewModuleConfig().
diff --git a/vfs/vfs.go b/vfs/vfs.go
index d7577ed..a63ed21 100644
--- a/vfs/vfs.go
+++ b/vfs/vfs.go
@@ -77,13 +77,13 @@ func vfsLocaltime(ctx context.Context, mod api.Module, pTm uint32, t int64) _Err
 	return _OK
 }
 
-func vfsRandomness(ctx context.Context, mod api.Module, pVfs, nByte, zByte uint32) uint32 {
+func vfsRandomness(ctx context.Context, mod api.Module, pVfs uint32, nByte int32, zByte uint32) uint32 {
 	mem := util.View(mod, zByte, uint64(nByte))
 	n, _ := rand.Reader.Read(mem)
 	return uint32(n)
 }
 
-func vfsSleep(ctx context.Context, mod api.Module, pVfs, nMicro uint32) _ErrorCode {
+func vfsSleep(ctx context.Context, mod api.Module, pVfs uint32, nMicro int32) _ErrorCode {
 	osSleep(time.Duration(nMicro) * time.Microsecond)
 	return _OK
 }
@@ -95,19 +95,16 @@ func vfsCurrentTime64(ctx context.Context, mod api.Module, pVfs, piNow uint32) _
 	return _OK
 }
 
-func vfsFullPathname(ctx context.Context, mod api.Module, pVfs, zRelative, nFull, zFull uint32) _ErrorCode {
+func vfsFullPathname(ctx context.Context, mod api.Module, pVfs, zRelative uint32, nFull int32, zFull uint32) _ErrorCode {
 	vfs := vfsGet(mod, pVfs)
 	path := util.ReadString(mod, zRelative, _MAX_PATHNAME)
 
 	path, err := vfs.FullPathname(path)
 
-	size := uint64(len(path) + 1)
-	if size > uint64(nFull) {
+	if len(path) >= int(nFull) {
 		return _CANTOPEN_FULLPATH
 	}
-	mem := util.View(mod, zFull, size)
-	mem[len(path)] = 0
-	copy(mem, path)
+	util.WriteString(mod, zFull, path)
 
 	return vfsErrorCode(err, _CANTOPEN_FULLPATH)
 }
@@ -185,7 +182,7 @@ func vfsClose(ctx context.Context, mod api.Module, pFile uint32) _ErrorCode {
 	return _OK
 }
 
-func vfsRead(ctx context.Context, mod api.Module, pFile, zBuf, iAmt uint32, iOfst int64) _ErrorCode {
+func vfsRead(ctx context.Context, mod api.Module, pFile, zBuf uint32, iAmt int32, iOfst int64) _ErrorCode {
 	file := vfsFileGet(ctx, mod, pFile)
 	buf := util.View(mod, zBuf, uint64(iAmt))
 
@@ -200,7 +197,7 @@ func vfsRead(ctx context.Context, mod api.Module, pFile, zBuf, iAmt uint32, iOfs
 	return _IOERR_SHORT_READ
 }
 
-func vfsWrite(ctx context.Context, mod api.Module, pFile, zBuf, iAmt uint32, iOfst int64) _ErrorCode {
+func vfsWrite(ctx context.Context, mod api.Module, pFile, zBuf uint32, iAmt int32, iOfst int64) _ErrorCode {
 	file := vfsFileGet(ctx, mod, pFile)
 	buf := util.View(mod, zBuf, uint64(iAmt))
 
@@ -358,7 +355,12 @@ func vfsDeviceCharacteristics(ctx context.Context, mod api.Module, pFile uint32)
 
 var shmBarrier sync.Mutex
 
-func vfsShmMap(ctx context.Context, mod api.Module, pFile, iRegion, szRegion, bExtend, pp uint32) _ErrorCode {
+func vfsShmBarrier(ctx context.Context, mod api.Module, pFile uint32) {
+	shmBarrier.Lock()
+	defer shmBarrier.Unlock()
+}
+
+func vfsShmMap(ctx context.Context, mod api.Module, pFile uint32, iRegion, szRegion int32, bExtend, pp uint32) _ErrorCode {
 	file := vfsFileGet(ctx, mod, pFile).(fileShm)
 	p, err := file.shmMap(ctx, mod, iRegion, szRegion, bExtend != 0)
 	if err != nil {
@@ -368,7 +370,7 @@ func vfsShmMap(ctx context.Context, mod api.Module, pFile, iRegion, szRegion, bE
 	return _OK
 }
 
-func vfsShmLock(ctx context.Context, mod api.Module, pFile, offset, n uint32, flags _ShmFlag) _ErrorCode {
+func vfsShmLock(ctx context.Context, mod api.Module, pFile uint32, offset, n int32, flags _ShmFlag) _ErrorCode {
 	file := vfsFileGet(ctx, mod, pFile).(fileShm)
 	err := file.shmLock(offset, n, flags)
 	return vfsErrorCode(err, _IOERR_SHMLOCK)
@@ -380,11 +382,6 @@ func vfsShmUnmap(ctx context.Context, mod api.Module, pFile, bDelete uint32) _Er
 	return _OK
 }
 
-func vfsShmBarrier(ctx context.Context, mod api.Module, pFile uint32) {
-	shmBarrier.Lock()
-	defer shmBarrier.Unlock()
-}
-
 func vfsURIParameters(ctx context.Context, mod api.Module, zPath uint32, flags OpenFlag) url.Values {
 	if flags&OPEN_URI == 0 {
 		return nil
@@ -465,9 +462,3 @@ func vfsErrorCode(err error, def _ErrorCode) _ErrorCode {
 	}
 	return def
 }
-
-type fileShm interface {
-	shmMap(context.Context, api.Module, uint32, uint32, bool) (uint32, error)
-	shmLock(uint32, uint32, _ShmFlag) error
-	shmUnmap(bool)
-}
diff --git a/vfs/vfs_test.go b/vfs/vfs_test.go
index 872ca07..49511ab 100644
--- a/vfs/vfs_test.go
+++ b/vfs/vfs_test.go
@@ -225,7 +225,7 @@ func Test_vfsFile(t *testing.T) {
 	// Write stuff.
 	text := "Hello world!"
 	util.WriteString(mod, 16, text)
-	rc = vfsWrite(ctx, mod, 4, 16, uint32(len(text)), 0)
+	rc = vfsWrite(ctx, mod, 4, 16, int32(len(text)), 0)
 	if rc != _OK {
 		t.Fatal("returned", rc)
 	}
@@ -240,7 +240,7 @@ func Test_vfsFile(t *testing.T) {
 	}
 
 	// Partial read at offset.
-	rc = vfsRead(ctx, mod, 4, 16, uint32(len(text)), 4)
+	rc = vfsRead(ctx, mod, 4, 16, int32(len(text)), 4)
 	if rc != _IOERR_SHORT_READ {
 		t.Fatal("returned", rc)
 	}