Implement basic support for JSaddle special device

fs.js

@@ -5,6 +5,24 @@ if(typeof exports !== 'undefined'){
 var bfs = BrowserFS.BFSRequire('fs');
 var bfs_utils = BrowserFS.BFSRequire('bfs_utils');
 
+// Sub-worker, collecting incoming messages from JS side jsaddle
+var jsaddleListener = new Worker('jsaddle_listener.js');
+
+// SharedArrayBuffer to communicate between wasm and jsaddleListener workers
+// Just for incoming messages/SYS_read
+// The write can happen via non-blocking postMessage
+//
+// The wasm worker is supposed to read one incoming message at a time
+// So this buffer will contain only one message at a time.
+
+// First UInt (32 bits), indicate buffer data size
+// Followed by data
+var jsaddleMsgSharedBuf = new SharedArrayBuffer(1024*1024);
+var jsaddleMsgBufArray = new Uint8Array(jsaddleMsgSharedBuf);
+var jsaddleMsgBufArray32 = new Uint32Array(jsaddleMsgSharedBuf);
+
+var JSADDLE_INOUT_FD = 4;
+var JSADDLE_INOUT_DEV = "/dev/jsaddle_inout";
 
 // Certain directories are required by POSIX (and musl). In case there is an
 // in memory filesystem under root we need to take care to create these manually.
@@ -96,28 +114,79 @@ function catchApiError(f) {
 }
 
 var fs = {
+
+  initFsJSaddle: function (jsaddleChannelPort) {
+    jsaddleListener.postMessage(
+      {type: 'init'
+       , jsaddleMsgBufArray32: jsaddleMsgBufArray32
+       , jsaddleMsgBufArray: jsaddleMsgBufArray
+       , jsaddleChannelPort: jsaddleChannelPort}
+      , [jsaddleChannelPort]);
+  },
+
   openat: function (dirfd, pathname, flags, mode) {
-    if (dirfd !== AT_FDCWD) {
-      utils.warn('openat: TODO: dirfd other than AT_FDCWD, ignoring');
+    if (pathname == JSADDLE_INOUT_DEV) {
+      // FIXME set a valid value here
+      JSADDLE_INOUT_FD = 4;
+      return JSADDLE_INOUT_FD;
+    } else {
+      if (dirfd !== AT_FDCWD) {
+        utils.warn('openat: TODO: dirfd other than AT_FDCWD, ignoring');
+      }
+      return catchApiError(() => bfs.openSync(pathname, flagsToString(flags), mode));
     }
-    return catchApiError(() => bfs.openSync(pathname, flagsToString(flags), mode));
   },
 
   creat: function (pathname, mode) {
     return this.openat(AT_FDCWD, pathname, O_CREAT|O_WRONLY|O_TRUNC, mode);
   },
 
   read: function (fd, buf, offset, count) {
-    var b = bfs_utils.uint8Array2Buffer(buf);
-    return catchApiError(() => bfs.readSync(fd, b, offset, count, null));
+    if (fd === JSADDLE_INOUT_FD) {
+      var bytes_read = 0;
+      var bytes_available = jsaddleMsgBufArray32[0];
+      if (bytes_available > 0) {
+        if (bytes_available > count) {
+          var i = count;
+          bytes_read = i;
+          while (i--) buf[offset + i] = jsaddleMsgBufArray[i + 4];
+
+          // Shift the remaining contents, and set size
+          var target = 4;
+          var start = count + 4 + 1;
+          var len = bytes_available - count;
+          jsaddleMsgBufArray.copyWithin(target, start, len);
+          jsaddleMsgBufArray32[0] = len;
+        } else {
+          var i = bytes_available;
+          bytes_read = bytes_available;
+          while (i--) buf[offset + i] = jsaddleMsgBufArray[i + 4];
+          //buf[offset + bytes_available + 1] = 0;
+
+          // Set remaining bytes to 0
+          jsaddleMsgBufArray32[0] = 0;
+          // Tell jsaddle listener that buffer has been read
+          jsaddleListener.postMessage({type: 'read'});
+        }
+      }
+      return bytes_read;
+    } else {
+      var b = bfs_utils.uint8Array2Buffer(buf);
+      return catchApiError(() => bfs.readSync(fd, b, offset, count, null));
+    }
   },
 
   write: function (fd, buf, offset, count) {
-    // stdout is handled specially here, we may have a more robust solution
-    // in the future that does not assume stdout is connected to console
-    if (fd === 1) {
+    // stdout and stderr are handled specially here, we may have a more robust solution
+    // in the future that does not assume they are connected to console
+    if ((fd === 1) || (fd === 2)) {
       utils.stdout__write(utils.bufToStr(buf, offset, offset + count));
       return count;
+    } else if (fd === JSADDLE_INOUT_FD) {
+      var a = new Uint8Array(buf.slice(offset, offset + count));
+      var b = a.buffer;
+      jsaddleListener.postMessage({type: 'write', buf: b}, [b]);
+      return count;
     } else {
       var b = bfs_utils.uint8Array2Buffer(buf);
       return catchApiError(() => bfs.writeSync(fd, b, offset, count, null));
@@ -198,9 +267,24 @@ var fs = {
 
   ftruncate: function (fd, length) {
     return catchApiError(() => bfs.ftruncate(fd, length));
+  },
+
+  fstat64: function (fd, statbuf_) {
+    if (fd === JSADDLE_INOUT_FD) {
+      // Set device type in st_mode field
+      // S_IFCHR    0020000   character device (octal)
+      // sizeof (st_dev) 8
+      // sizeof (st_ino) 8
+      // sizeof (st_mode) 4
+      st_mode_ptr = (statbuf_ + 16) / 4;
+      heap_uint32[st_mode_ptr] = 8192;
+      return 0;
+    } else {
+      throw "SYS_fstat64 NYI";
+    }
   }
 };
 
-if(typeof exports !== 'undefined'){
+if (typeof exports !== 'undefined'){
   module.exports = fs;
 }