Implement writeBuffers using writev and pwritev syscalls.

Change-Type: patch

lib/binding.js

@@ -15,7 +15,7 @@ function getCallback(req) {
 }
 
 function addNullTerminationIfNeeded(s) {
-	// If the s is a Buffer, we need to add a NULL termination byte.
+	// If s is a Buffer, we need to add a NULL termination byte.
 	if (Buffer.isBuffer(s)) {
 		const nullTerminated = Buffer.allocUnsafe(s.length + 1);
 		s.copy(nullTerminated);
@@ -193,8 +193,21 @@ exports.writeBuffer = function(fd, buffer, offset, length, position, req) {
 	}
 }
 
-exports.writeBuffers = function() {
-	throw new Error('Unimplemented');
+exports.writeBuffers = function(fd, buffers, position, req) {
+	const callback = getCallback(req);
+	const iovecs = bindings.buffersToIoVecs(buffers);
+	if (typeof position === 'number' && position !== -1) {
+		return syscall.pwritev(
+			fd,
+			iovecs,
+			buffers.length,
+			position & 0xffffffff,  // 32 lower bits
+			Math.floor(position / Math.pow(2, 32)),  // high bits
+			callback
+		);
+	} else {
+		return syscall.writev(fd, iovecs, buffers.length, callback);
+	}
 }
 
 exports.writeString = function() {

lib/syscall.js

@@ -47,6 +47,7 @@ module.exports = {
 	openat:        syscall.bind(null, constants.SYS_openat),
 	pread64:       syscall.bind(null, constants.SYS_pread64),
 	pwrite64:      syscall.bind(null, constants.SYS_pwrite64),
+	pwritev:       syscall.bind(null, constants.SYS_pwritev),
 	read:          syscall.bind(null, constants.SYS_read),
 	readlinkat:    syscall.bind(null, constants.SYS_readlinkat),
 	removexattr:   syscall.bind(null, constants.SYS_removexattr),
@@ -56,7 +57,8 @@ module.exports = {
 	sync:          syscall.bind(null, constants.SYS_sync),
 	truncate:      syscall.bind(null, constants.SYS_truncate),
 	unlinkat:      syscall.bind(null, constants.SYS_unlinkat),
-	write:         syscall.bind(null, constants.SYS_write)
+	write:         syscall.bind(null, constants.SYS_write),
+	writev:        syscall.bind(null, constants.SYS_writev)
 };
 
 // Unimplemented syscalls

src/bindings.cc

@@ -11,6 +11,7 @@ NAN_MODULE_INIT(InitAll) {
 	NAN_EXPORT(target, sizeOfStructLklStat);
 	NAN_EXPORT(target, parseLklStat);
 	NAN_EXPORT(target, millisecondsToTimespec);
+	NAN_EXPORT(target, buffersToIoVecs);
 }
 
 NODE_MODULE(bindings, InitAll)

src/node_lkl.cc

@@ -187,3 +187,19 @@ NAN_METHOD(millisecondsToTimespec) {
 	).ToLocalChecked();
 	info.GetReturnValue().Set(result);
 }
+
+NAN_METHOD(buffersToIoVecs) {
+	auto arr = info[0].As<v8::Array>();
+	auto len = arr->Length();
+	auto *iovecs = new struct iovec[len];
+	for (unsigned int i = 0; i < len; i++) {
+		auto buf = arr->Get(i);
+		iovecs[i].iov_base = reinterpret_cast<char*>(node::Buffer::Data(buf));
+		iovecs[i].iov_len = node::Buffer::Length(buf);
+	}
+	auto result = Nan::NewBuffer(
+		reinterpret_cast<char*>(iovecs),
+		sizeof *iovecs
+	).ToLocalChecked();
+	info.GetReturnValue().Set(result);
+}

src/node_lkl.h

@@ -7,3 +7,4 @@ NAN_METHOD(parseDirent64);
 NAN_METHOD(sizeOfStructLklStat);
 NAN_METHOD(parseLklStat);
 NAN_METHOD(millisecondsToTimespec);
+NAN_METHOD(buffersToIoVecs);

test/index.js

@@ -372,5 +372,31 @@ describe('node-lkl', function() {
 				.then(done);
 			});
 		});
+
+		describe('writev', function() {
+			it('should write all buffers to file', function(done) {
+				const fpath = path.join(this.mountpoint, 'filename');
+				const stream = lkl.fs.WriteStream(fpath);
+				const chunks = [
+					{chunk: Buffer.from('1')},
+					{chunk: Buffer.from('2')},
+					{chunk: Buffer.from('3')},
+				]
+				// testing writev syscall
+				stream._writev(chunks, function(err) {
+					// testing pwritev syscall
+					stream.pos = 1;
+					stream._writev(chunks, function(err) {
+						stream.close(function(err){
+							lkl.fs.readFileAsync(fpath, 'utf8')
+							.then(function(content) {
+								assert.strictEqual(content, '1123', 'should read what it has written');
+								done();
+							})
+						})
+					});
+				});
+			});
+		});
 	});
 });