Readonly shared memory.

Author: ncruces

internal/testcfg/testcfg.go

@@ -19,7 +19,8 @@ func init() {
 		path := filepath.Join(os.TempDir(), "wazero")
 		if err := os.MkdirAll(path, 0777); err == nil {
 			if cache, err := wazero.NewCompilationCacheWithDir(path); err == nil {
-				sqlite3.RuntimeConfig.WithCompilationCache(cache)
+				sqlite3.RuntimeConfig = sqlite3.RuntimeConfig.
+					WithCompilationCache(cache)
 			}
 		}
 	}

vfs/shm.go

@@ -22,8 +22,5 @@ func NewSharedMemory(path string, flags OpenFlag) SharedMemory {
 	if flags&OPEN_MAIN_DB == 0 || flags&(OPEN_DELETEONCLOSE|OPEN_MEMORY) != 0 {
 		return nil
 	}
-	return &vfsShm{
-		path:     path,
-		readOnly: flags&OPEN_READONLY != 0,
-	}
+	return &vfsShm{path: path}
 }

vfs/shm_bsd.go

@@ -18,11 +18,9 @@ type vfsShmFile struct {
 	*os.File
 	info os.FileInfo
 
-	// +checklocks:vfsShmFilesMtx
-	refs int
+	refs int // +checklocks:vfsShmFilesMtx
 
-	// +checklocks:Mutex
-	lock [_SHM_NLOCK]int16
+	lock [_SHM_NLOCK]int16 // +checklocks:Mutex
 	sync.Mutex
 }
 
@@ -34,10 +32,9 @@ var (
 
 type vfsShm struct {
 	*vfsShmFile
-	path     string
-	lock     [_SHM_NLOCK]bool
-	regions  []*util.MappedRegion
-	readOnly bool
+	path    string
+	lock    [_SHM_NLOCK]bool
+	regions []*util.MappedRegion
 }
 
 func (s *vfsShm) Close() error {
@@ -69,7 +66,7 @@ func (s *vfsShm) Close() error {
 	panic(util.AssertErr())
 }
 
-func (s *vfsShm) shmOpen() (rc _ErrorCode) {
+func (s *vfsShm) shmOpen() _ErrorCode {
 	if s.vfsShmFile != nil {
 		return _OK
 	}
@@ -100,17 +97,13 @@ func (s *vfsShm) shmOpen() (rc _ErrorCode) {
 		}
 	}
 
-	// Lock and truncate the file, if not readonly.
+	// Lock and truncate the file.
 	// The lock is only released by closing the file.
-	if s.readOnly {
-		rc = _READONLY_CANTINIT
-	} else {
-		if rc := osLock(f, unix.LOCK_EX|unix.LOCK_NB, _IOERR_LOCK); rc != _OK {
-			return rc
-		}
-		if err := f.Truncate(0); err != nil {
-			return _IOERR_SHMOPEN
-		}
+	if rc := osLock(f, unix.LOCK_EX|unix.LOCK_NB, _IOERR_LOCK); rc != _OK {
+		return rc
+	}
+	if err := f.Truncate(0); err != nil {
+		return _IOERR_SHMOPEN
 	}
 
 	// Add the new shared file.
@@ -122,11 +115,11 @@ func (s *vfsShm) shmOpen() (rc _ErrorCode) {
 	for i, g := range vfsShmFiles {
 		if g == nil {
 			vfsShmFiles[i] = s.vfsShmFile
-			return rc
+			return _OK
 		}
 	}
 	vfsShmFiles = append(vfsShmFiles, s.vfsShmFile)
-	return rc
+	return _OK
 }
 
 func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, extend bool) (uint32, _ErrorCode) {
@@ -148,25 +141,17 @@ func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, ext
 		if !extend {
 			return 0, _OK
 		}
-		if s.readOnly || osAllocate(s.File, n) != nil {
+		if osAllocate(s.File, n) != nil {
 			return 0, _IOERR_SHMSIZE
 		}
 	}
 
-	var prot int
-	if s.readOnly {
-		prot = unix.PROT_READ
-	} else {
-		prot = unix.PROT_READ | unix.PROT_WRITE
-	}
-	r, err := util.MapRegion(ctx, mod, s.File, int64(id)*int64(size), size, prot)
+	r, err := util.MapRegion(ctx, mod, s.File, int64(id)*int64(size), size,
+		unix.PROT_READ|unix.PROT_WRITE)
 	if err != nil {
 		return 0, _IOERR_SHMMAP
 	}
 	s.regions = append(s.regions, r)
-	if s.readOnly {
-		return r.Ptr, _READONLY
-	}
 	return r.Ptr, _OK
 }
 

vfs/shm_copy.go renamed to vfs/shm_dotlk.go

@@ -4,6 +4,9 @@ package vfs
 
 import (
 	"context"
+	"errors"
+	"io/fs"
+	"os"
 	"sync"
 	"unsafe"
 
@@ -29,15 +32,14 @@ var (
 
 type vfsShm struct {
 	*vfsShmBuffer
-	mod      api.Module
-	alloc    api.Function
-	free     api.Function
-	path     string
-	shadow   []byte
-	ptrs     []uint32
-	stack    [1]uint64
-	lock     [_SHM_NLOCK]bool
-	readOnly bool
+	mod    api.Module
+	alloc  api.Function
+	free   api.Function
+	path   string
+	shadow []byte
+	ptrs   []uint32
+	stack  [1]uint64
+	lock   [_SHM_NLOCK]bool
 }
 
 func (s *vfsShm) Close() error {
@@ -58,13 +60,18 @@ func (s *vfsShm) Close() error {
 		return nil
 	}
 
+	err := os.Remove(s.path)
+	if err != nil && !errors.Is(err, fs.ErrNotExist) {
+		return _IOERR_UNLOCK
+	}
 	delete(vfsShmBuffers, s.path)
+	s.vfsShmBuffer = nil
 	return nil
 }
 
-func (s *vfsShm) shmOpen() {
+func (s *vfsShm) shmOpen() _ErrorCode {
 	if s.vfsShmBuffer != nil {
-		return
+		return _OK
 	}
 
 	vfsShmBuffersMtx.Lock()
@@ -74,12 +81,23 @@ func (s *vfsShm) shmOpen() {
 	if g, ok := vfsShmBuffers[s.path]; ok {
 		s.vfsShmBuffer = g
 		g.refs++
-		return
+		return _OK
+	}
+
+	// Create a directory on disk to ensure only this process
+	// uses this path to register a shared memory.
+	err := os.Mkdir(s.path, 0777)
+	if errors.Is(err, fs.ErrExist) {
+		return _BUSY
+	}
+	if err != nil {
+		return _IOERR_LOCK
 	}
 
 	// Add the new shared buffer.
 	s.vfsShmBuffer = &vfsShmBuffer{}
 	vfsShmBuffers[s.path] = s.vfsShmBuffer
+	return _OK
 }
 
 func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, extend bool) (uint32, _ErrorCode) {
@@ -91,8 +109,10 @@ func (s *vfsShm) shmMap(ctx context.Context, mod api.Module, id, size int32, ext
 		s.free = mod.ExportedFunction("sqlite3_free")
 		s.alloc = mod.ExportedFunction("sqlite3_malloc64")
 	}
+	if rc := s.shmOpen(); rc != _OK {
+		return 0, rc
+	}
 
-	s.shmOpen()
 	s.Lock()
 	defer s.Unlock()
 	defer s.shmAcquire()

vfs/shm_ofd.go

@@ -28,14 +28,13 @@ var _ blockingSharedMemory = &vfsShm{}
 
 func (s *vfsShm) shmOpen() _ErrorCode {
 	if s.File == nil {
-		var flag int
-		if s.readOnly {
-			flag = unix.O_RDONLY
-		} else {
-			flag = unix.O_RDWR
-		}
 		f, err := os.OpenFile(s.path,
-			flag|unix.O_CREAT|unix.O_NOFOLLOW, 0666)
+			unix.O_RDWR|unix.O_CREAT|unix.O_NOFOLLOW, 0666)
+		if err != nil {
+			f, err = os.OpenFile(s.path,
+				unix.O_CREAT|unix.O_NOFOLLOW, 0666)
+			s.readOnly = true
+		}
 		if err != nil {
 			return _CANTOPEN
 		}