X keeping fd to root opened prevents the filesystem from being unmounted

wcfs/wcfs.go

@@ -540,18 +540,18 @@ func (r *Root) zwatcher(ctx context.Context) (err error) {
 }
 
 // zhandle1 handles 1 event from ZODB notification.
-// (called with .zheadMu wlocked)
 func (r *Root) zhandle1(zevent zodb.WatchEvent) {
 	// XXX locking correct? XXX too coarse? -> lock only around "resync .zhead ..." ?
-	r.zheadMu.Lock()
-	defer r.zheadMu.Unlock()
+	r.head.zconnMu.Lock()
+	defer r.head.zconnMu.Unlock()
+	zhead := r.head.zconn
 
 	//toinvalidate := map[*ZBigFile]SetI64{} // {} zfile -> set(#blk)
 	toinvalidate := map[*BigFile]SetI64{} // {} zfile -> set(#blk)
 
 	// zevent = (tid^, []oid)
 	for _, oid := range zevent.Changev {
-		obj := r.zhead.Cache().Get(oid)
+		obj := zhead.Cache().Get(oid)
 		if obj == nil {
 			continue // nothing to do - see invariant
 		}
@@ -597,12 +597,15 @@ func (r *Root) zhandle1(zevent zodb.WatchEvent) {
 }
 
 // invalidateBlk invalidates 1 file block.	XXX
+//
+// called with f.head.zconnMu wlocked.
+//
 // XXX see "4.4) for all file/blk to in invalidate we do"
 func (f *BigFile) invalidateBlk(ctx context.Context, blk int64) error {
-	fsconn := f.root().fsconn
+	fsconn := gfsconn
 	off := blk*blksize
 
-	// try retrieve cache of current head/data[blk]
+	// try to retrieve cache of current head/data[blk]
 	//
 	// if less than blksize was cached - probably the kernel had to evict
 	// some data from its cache already. In such case we don't try to
@@ -610,11 +613,13 @@ func (f *BigFile) invalidateBlk(ctx context.Context, blk int64) error {
 	// system overloaded.
 	//
 	// XXX st != OK -> warn?
-	blkdata, st := fsconn.FileRetrieveCache(f.Inode(), off, blksize)
-	if len(blkdata) == blksize {
+	blkdata := make([]byte, blksize)
+	n, st := fsconn.FileRetrieveCache(f.Inode(), off, blkdata)
+	if n == blksize {
 		// XXX -> go
-		// store retrieved data back to OS cache for file @<rev>/data[blk]
-		frev, _ := f.bigfile.δFtail.LastRevOf(blk, at)
+		// store retrieved data back to OS cache for file @<rev>/file[blk]
+		blkrev, _ := f.δFtail.LastRevOf(blk, f.head.zconn.At())
+		frev := groot.revisionedFile(ctx, blkrev, f.zbf.POid())
 		st = fsconn.FileNotifyStoreCache(frev.Inode(), off, blkdata)
 		if st != fuse.OK {
 			// XXX log	- dup wrt readBlk -> common func.
@@ -627,6 +632,18 @@ func (f *BigFile) invalidateBlk(ctx context.Context, blk int64) error {
 
 	panic("TODO")
 }
+
+
+// mkrevfile makes sure inode of /@<rev>/bigfile/<fid> is known to kernel.
+//
+// We need node ID to be know to the kernel, when we need to store data into
+// file's kernel cache.
+//
+// For kernel to know node IDmkrevfile has
+//
+// XXX why we go through kernel.lookup
+func (root *Root) mkrevfile(ctx context.Context, rev zodb.Tid, fid zodb.Oid) (*BigFile, error) {
+}
 */
 
 // ----------------------------------------
@@ -960,7 +977,7 @@ func (f *BigFile) readBlk(ctx context.Context, blk int64, dest []byte) error {
 	_ = revmax
 
 /*
-	// XXX remmapping
+	// XXX remmapping - only if head.rev == 0
 	// XXX -> own func?
 	// XXX locking
 	for _, mapping := range f.mappings {
@@ -1050,9 +1067,12 @@ func (h *Head) readAt() []byte {
 //	- Mount:
 //		.Root()		-> root Inode of the fs
 //		.Connector()	-> FileSystemConnector through which fs is mounted
-//var groot   *Root
+var groot   *Root
 var gfsconn *nodefs.FileSystemConnector
 
+// file descriptor for opened root of the filesystem
+var grootf *os.File // XXX -> fd
+
 func main() {
 	stdlog.SetPrefix("wcfs: ")
 	//log.CopyStandardLogTo("WARNING") // XXX -> "DEBUG" if -d ?
@@ -1116,7 +1136,7 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
-	//groot   = root		// FIXME temp workaround (see ^^^)
+	groot   = root		// FIXME temp workaround (see ^^^)
 	gfsconn = fsconn	// FIXME ----//----
 
 	// we require proper pagecache control (added to Linux 2.6.36 in 2010)
@@ -1139,5 +1159,22 @@ func main() {
 	_ = autoexit
 
 	// serve client requests
-	fssrv.Serve()	// XXX Serve returns no error
+	done := make(chan struct{})
+	go func() {
+		fssrv.Serve()	// XXX Serve returns no error
+		close(done)
+	}()
+
+	err = fssrv.WaitMount()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	grootf, err = os.Open(mntpt)
+	if err != nil {
+		fssrv.Unmount()
+		log.Fatal(err)
+	}
+
+	<-done
 }