X Change FileSock to use xio.Pipe which is io.Pipe + support for IO cancellation

We need to do this because when e.g. a thread in client process dies and
wants to abort the whole process, kernel sends FUSE INTERRUPT request to
interrup READ syscall on-client pinner is waiting on for /head/watch.
And if this cancellation is not handled, the client process is left hang
forever and even kill -9 does not stop it.

xio.Pipe to be committed/pushed yet to go123.

test_wcfs_watch_robust becomes broken for now.

wcfs/misc.go

@@ -39,6 +39,7 @@ import (
 	"github.com/pkg/errors"
 
 	"lab.nexedi.com/kirr/go123/xcontext"
+	"lab.nexedi.com/kirr/go123/xio"
 
 	"lab.nexedi.com/kirr/neo/go/transaction"
 	"lab.nexedi.com/kirr/neo/go/zodb"
@@ -271,9 +272,9 @@ func mount(mntpt string, root nodefs.Node, opts *fuse.MountOptions) (*fuse.Serve
 // FileSock provides streaming write/read operations for filesystem server that
 // are correspondingly matched with read/write operations on filesystem user side.
 type FileSock struct {
-	file *skFile        // filesock's file peer
-	rx   *io.PipeReader // socket reads from file here
-	tx   *io.PipeWriter // socket writes to file here
+	file *skFile         // filesock's file peer
+	rx   *xio.PipeReader // socket reads from file here
+	tx   *xio.PipeWriter // socket writes to file here
 }
 
 // skFile is File peer of FileSock.
@@ -286,8 +287,8 @@ type FileSock struct {
 type skFile struct {
 	nodefs.File
 
-	rx *io.PipeReader // file reads from socket here
-	tx *io.PipeWriter // file writes to socket here
+	rx *xio.PipeReader // file reads from socket here
+	tx *xio.PipeWriter // file writes to socket here
 }
 
 // NewFileSock creates new file socket.
@@ -301,11 +302,11 @@ func NewFileSock() *FileSock {
 	}
 	sk.file = f
 
-	rx, tx := io.Pipe()
+	rx, tx := xio.Pipe()
 	sk.rx = rx
 	f .tx = tx
 
-	rx, tx = io.Pipe()
+	rx, tx = xio.Pipe()
 	f .rx = rx
 	sk.tx = tx
 
@@ -332,15 +333,15 @@ func (sk *FileSock) File() nodefs.File {
 // Write writes data to filesock.
 //
 // The data will be read by client reading from filesock's file.
-// Write semantic is that of io.Writer.
-func (sk *FileSock) Write(data []byte) (n int, err error) {
+// Write semantic is that of xio.Writer.
+func (sk *FileSock) Write(ctx context.Context, data []byte) (n int, err error) {
 	// XXX err ctx?
-	return sk.tx.Write(data)
+	return sk.tx.Write(ctx, data)
 }
 
 // Read implements nodefs.File and is paired with filesock.Write().
 func (f *skFile) Read(dest []byte, /*ignored*/off int64, fctx *fuse.Context) (fuse.ReadResult, fuse.Status) {
-	n, err := f.rx.Read(dest)	// XXX fctx.cancel
+	n, err := f.rx.Read(fctx, dest)
 	if n != 0 {
 		err = nil
 	}
@@ -358,10 +359,10 @@ func (f *skFile) Read(dest []byte, /*ignored*/off int64, fctx *fuse.Context) (fu
 // Read reads data from filesock.
 //
 // The data read will be that the client writes into filesock's file.
-// Read semantic is that of io.Reader.
-func (sk *FileSock) Read(dest []byte) (n int, err error) {
+// Read semantic is that of xio.Reader.
+func (sk *FileSock) Read(ctx context.Context, dest []byte) (n int, err error) {
 	// XXX err ctx?
-	return sk.rx.Read(dest)
+	return sk.rx.Read(ctx, dest)
 }
 
 // Write implements nodefs.File and is paired with filesock.Read()
@@ -373,7 +374,7 @@ func (f *skFile) Write(data []byte, /*ignored*/off int64, fctx *fuse.Context) (u
 		data = data[:l]
 	}
 
-	n, err := f.tx.Write(data)	// XXX fctx.cancel
+	n, err := f.tx.Write(fctx, data)
 	if n != 0 {
 		err = nil
 	}

wcfs/wcfs.go

@@ -491,6 +491,7 @@ import (
 
 	"lab.nexedi.com/kirr/go123/xcontext"
 	"lab.nexedi.com/kirr/go123/xerr"
+	"lab.nexedi.com/kirr/go123/xio"
 
 	"lab.nexedi.com/kirr/neo/go/transaction"
 	"lab.nexedi.com/kirr/neo/go/zodb"
@@ -924,7 +925,7 @@ retry:
 
 	// notify .wcfs/zhead
 	for sk := range gdebug.zheadSockTab {
-		_, err := fmt.Fprintf(sk, "%s\n", δZ.Tid)
+		_, err := fmt.Fprintf(xio.BindWriter(sk, ctx), "%s\n", δZ.Tid)
 		if err != nil {
 			log.Errorf("%s", err)	// XXX errctx + file, handle, reader pid
 			sk.Close()
@@ -1731,13 +1732,14 @@ func (wlink *WatchLink) serve() {
 
 func (wlink *WatchLink) _serve() (err error) {
 	defer xerr.Contextf(&err, "wlink %d: serve rx", wlink.id)
-	r := bufio.NewReader(wlink.sk)
 
 	ctx0 := context.TODO()	// XXX ctx = ? -> merge(ctx of wcfs running, ctx of wlink timeout)
 
 	ctx, cancel := context.WithCancel(ctx0)
 	wg, ctx := errgroup.WithContext(ctx)
 
+	r := bufio.NewReader(xio.BindReader(wlink.sk, ctx))
+
 	defer func() {
 		// cancel all handlers on both error and ok return.
 		// ( ok return is e.g. when we received "bye", so if client
@@ -1908,10 +1910,9 @@ func (wlink *WatchLink) send(ctx context.Context, stream uint64, msg string) err
 	wlink.txMu.Lock()
 	defer wlink.txMu.Unlock()
 
-	// XXX timeout write on ctx cancel
 	pkt := []byte(fmt.Sprintf("%d %s\n", stream, msg))
 	fmt.Printf("S: wlink %d: tx: %q\n", wlink.id, pkt)
-	_, err := wlink.sk.Write(pkt)
+	_, err := wlink.sk.Write(ctx, pkt)
 	if err != nil {
 		return err
 	}