ethernet: Get rid of the read/write buffers for scattered I/O.

This (mostly) reverts commit 3ea7c99119.

We no longer need this code after introducing the calls to send
net_buffers to drivers directly.

Change-Id: I31a2fdbbbe8203c53dbcc1e3b1fab2492c8651bd
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7914
Reviewed-by: waddlesplash <[email protected]>

src/add-ons/kernel/network/devices/ethernet/ethernet.cpp

@@ -31,18 +31,9 @@
 
 
 struct ethernet_device : net_device, DoublyLinkedListLinkImpl<ethernet_device> {
-	~ethernet_device()
-	{
-		free(read_buffer);
-		free(write_buffer);
-	}
-
 	int		fd;
 	uint32	frame_size;
 	bool	supports_net_buffer;
-
-	void* read_buffer, *write_buffer;
-	mutex read_buffer_lock, write_buffer_lock;
 };
 
 static const bigtime_t kLinkCheckInterval = 1000000;
@@ -165,9 +156,6 @@ ethernet_init(const char *name, net_device **_device)
 	device->media = IFM_ACTIVE | IFM_ETHER;
 	device->header_length = ETHER_HEADER_LENGTH;
 	device->fd = -1;
-	device->read_buffer = device->write_buffer = NULL;
-	device->read_buffer_lock = MUTEX_INITIALIZER("ethernet read_buffer"),
-	device->write_buffer_lock = MUTEX_INITIALIZER("ethernet write_buffer");
 
 	*_device = device;
 	return B_OK;
@@ -232,19 +220,6 @@ ethernet_up(net_device *_device)
 		sCheckList.Add(device);
 	}
 
-	if (device->frame_size > ETHER_MAX_FRAME_SIZE) {
-		free(device->read_buffer);
-		free(device->write_buffer);
-
-		device->read_buffer = malloc(device->frame_size);
-		device->write_buffer = malloc(device->frame_size);
-
-		if (device->read_buffer == NULL || device->write_buffer == NULL) {
-			errno = B_NO_MEMORY;
-			goto err;
-		}
-	}
-
 	device->address.length = ETHER_ADDRESS_LENGTH;
 	device->mtu = device->frame_size - device->header_length;
 	return B_OK;
@@ -303,38 +278,25 @@ ethernet_send_data(net_device *_device, net_buffer *buffer)
 	net_buffer *allocated = NULL;
 	net_buffer *original = buffer;
 
-	MutexLocker bufferLocker;
-	struct iovec iovec;
 	if (gBufferModule->count_iovecs(buffer) > 1) {
-		if (device->write_buffer != NULL) {
+		// Create a new buffer containing the data.
-			bufferLocker.SetTo(device->write_buffer_lock, false);
+		buffer = gBufferModule->duplicate(original);
+		if (buffer == NULL)
+			return ENOBUFS;
 
-			status_t status = gBufferModule->read(buffer, 0,
+		allocated = buffer;
-				device->write_buffer, buffer->size);
-			if (status != B_OK)
-				return status;
-			iovec.iov_base = device->write_buffer;
-			iovec.iov_len = buffer->size;
-		} else {
-			// Fall back to creating a new buffer.
-			allocated = gBufferModule->duplicate(original);
-			if (allocated == NULL)
-				return ENOBUFS;
 
-			buffer = allocated;
+		if (gBufferModule->count_iovecs(buffer) > 1) {
-
+			dprintf("ethernet: net_buffer I/O is not supported by underlying device\n");
-			if (gBufferModule->count_iovecs(allocated) > 1) {
+			gBufferModule->free(buffer);
-				dprintf("ethernet_send_data: no write buffer, cannot perform scatter I/O\n");
+			device->stats.send.errors++;
-				gBufferModule->free(allocated);
+			return B_NOT_SUPPORTED;
-				return EMSGSIZE;
-			}
-
-			gBufferModule->get_iovecs(buffer, &iovec, 1);
 		}
-	} else {
-		gBufferModule->get_iovecs(buffer, &iovec, 1);
 	}
 
+	struct iovec iovec;
+	gBufferModule->get_iovecs(buffer, &iovec, 1);
+
 //dump_block((const char *)iovec.iov_base, buffer->size, "  ");
 	ssize_t bytesWritten = write(device->fd, iovec.iov_base, iovec.iov_len);
 //dprintf("sent: %ld\n", bytesWritten);
@@ -366,45 +328,32 @@ ethernet_receive_data(net_device *_device, net_buffer **_buffer)
 		return 0;
 	}
 
-	// TODO: better header space
+	// read/write only works for standard ethernet frames. For larger frames,
+	// the driver should support send/receive of net_buffers directly, above.
+
 	net_buffer *buffer = gBufferModule->create(256);
 	if (buffer == NULL)
 		return ENOBUFS;
 
-	MutexLocker bufferLocker;
-	struct iovec iovec;
 	ssize_t bytesRead;
-	status_t status;
+	void *data;
-	if (device->read_buffer != NULL) {
-		bufferLocker.SetTo(device->read_buffer_lock, false);
 
-		iovec.iov_base = device->read_buffer;
+	status_t status = gBufferModule->append_size(buffer, device->frame_size, &data);
-		iovec.iov_len = device->frame_size;
+	if (status == B_OK && data == NULL) {
-	} else {
+		dprintf("ethernet: net_buffer I/O is not supported by underlying device\n");
-		void *data;
+		status = B_NOT_SUPPORTED;
-		status = gBufferModule->append_size(buffer, device->frame_size, &data);
-		if (status == B_OK && data == NULL) {
-			dprintf("ethernet_receive_data: no read buffer, cannot perform scattered I/O!\n");
-			status = B_NOT_SUPPORTED;
-		}
-		if (status < B_OK)
-			goto err;
-
-		iovec.iov_base = data;
-		iovec.iov_len = device->frame_size;
 	}
+	if (status < B_OK)
+		goto err;
 
-	bytesRead = read(device->fd, iovec.iov_base, iovec.iov_len);
+	bytesRead = read(device->fd, data, device->frame_size);
 	if (bytesRead < 0) {
 		status = errno;
 		goto err;
 	}
 //dump_block((const char *)data, bytesRead, "rcv: ");
 
-	if (iovec.iov_base == device->read_buffer)
+	status = gBufferModule->trim(buffer, bytesRead);
-		status = gBufferModule->append(buffer, iovec.iov_base, bytesRead);
-	else
-		status = gBufferModule->trim(buffer, bytesRead);
 	if (status < B_OK) {
 		atomic_add((int32*)&device->stats.receive.dropped, 1);
 		goto err;