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fruity: Improve userspace NCM driver to perform batching
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As we observed packet loss in bursty situations, and implementing
batching avoids it.

Co-authored-by: Håvard Sørbø <[email protected]>
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@oleavr @hsorbo
oleavr and hsorbo committed Dec 8, 2024
1 parent 930776d commit 8d0b735
Showing 1 changed file with 160 additions and 32 deletions.
192 changes: 160 additions & 32 deletions src/fruity/ncm.vala
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Original file line number Diff line number Diff line change
Expand Up @@ -23,13 +23,29 @@ namespace Frida.Fruity {
}
}

private uint32 ntb_in_max_size;
private uint32 ntb_out_max_size;
private uint16 ndp_out_divisor;
private uint16 ndp_out_payload_remainder;
private uint16 ndp_out_alignment;
private uint16 ntb_out_max_datagrams;
private VirtualNetworkStack? _netstack;
private Gee.Queue<Bytes> pending_output = new Gee.ArrayQueue<Bytes> ();
private bool writing = false;
private uint16 next_outgoing_sequence = 1;

private InetAddress? _remote_ipv6_address;

private Cancellable io_cancellable = new Cancellable ();

private const uint16 TRANSFER_HEADER_SIZE = 4 + 2 + 2 + 2 + 2;

private enum CdcRequest {
GET_NTB_PARAMETERS = 0x80,
}

private const uint16 NTB_PARAMETERS_MIN_SIZE = 28;

private enum EtherType {
IPV6 = 0x86dd,
}
Expand Down Expand Up @@ -70,11 +86,31 @@ namespace Frida.Fruity {

unowned LibUSB.DeviceHandle handle = device.handle;
try {
Usb.check (handle.claim_interface (config.data_iface), "Failed to claim USB interface");
Usb.check (handle.claim_interface (config.ctrl_iface), "Failed to claim control interface");
Usb.check (handle.claim_interface (config.data_iface), "Failed to claim data interface");
} catch (Error e) {
throw new Error.PERMISSION_DENIED ("%s",
make_user_error_message (@"Unable to claim USB CDC-NCM interface ($(e.message))"));
}

var raw_ntb_params = yield device.control_transfer (
LibUSB.RequestRecipient.INTERFACE | LibUSB.RequestType.CLASS | LibUSB.EndpointDirection.IN,
CdcRequest.GET_NTB_PARAMETERS,
0,
config.ctrl_iface,
NTB_PARAMETERS_MIN_SIZE,
1000,
cancellable);
if (raw_ntb_params.get_size () < NTB_PARAMETERS_MIN_SIZE)
throw new Error.PROTOCOL ("Truncated NTB parameters response");
var ntb_params = new Buffer (raw_ntb_params, LITTLE_ENDIAN);
ntb_in_max_size = ntb_params.read_uint32 (4);
ntb_out_max_size = ntb_params.read_uint32 (16);
ndp_out_divisor = ntb_params.read_uint16 (20);
ndp_out_payload_remainder = ntb_params.read_uint16 (22);
ndp_out_alignment = ntb_params.read_uint16 (24);
ntb_out_max_datagrams = ntb_params.read_uint16 (26);

Usb.check (handle.set_interface_alt_setting (config.data_iface, config.data_altsetting),
"Failed to set USB interface alt setting");

Expand All @@ -92,7 +128,7 @@ namespace Frida.Fruity {
}

private async void process_incoming_datagrams () {
var data = new uint8[64 * 1024];
var data = new uint8[ntb_in_max_size];

while (true) {
try {
Expand Down Expand Up @@ -153,45 +189,134 @@ namespace Frida.Fruity {
} while (ndp_index != 0);
}

private async void on_netif_outgoing_datagram (Bytes datagram) {
uint16 transfer_header_length = 12;
uint16 ndp_header_length = 16;
uint16 alignment_padding_length = 2;
private void on_netif_outgoing_datagram (Bytes datagram) {
pending_output.offer (datagram);

if (!writing) {
writing = true;
var source = new IdleSource ();
source.set_callback (() => {
process_pending_output.begin ();
return false;
});
source.attach (MainContext.get_thread_default ());
}
}

uint16 datagram_start_index = transfer_header_length + ndp_header_length + alignment_padding_length;
uint16 datagram_length = (uint16) datagram.length;
private async void process_pending_output () {
while (!pending_output.is_empty) {
size_t num_datagrams = ntb_out_max_datagrams;
TransferLayout layout;
while ((layout = TransferLayout.compute (pending_output, num_datagrams, ndp_out_alignment,
ndp_out_divisor, ndp_out_payload_remainder)).size > ntb_out_max_size) {
num_datagrams--;
}

uint16 sentinel_start_index = 0;
uint16 sentinel_size = 0;
var batch = new Gee.ArrayList<Bytes> ();
for (var i = 0; i != layout.offsets.size; i++)
batch.add (pending_output.poll ());

uint16 sequence = next_outgoing_sequence++;
uint16 block_length = datagram_start_index + datagram_length;
uint16 ndp_index = transfer_header_length;
uint16 next_ndp_index = 0;
var transfer = build_output_transfer (batch, layout, next_outgoing_sequence++);

try {
yield device.bulk_transfer (config.tx_address, transfer.get_data (), uint.MAX, io_cancellable);
} catch (GLib.Error e) {
break;
}
}

writing = false;
}

private class TransferLayout {
public uint16 size;
public uint16 ndp_header_offset;
public uint16 ndp_header_size;
public Gee.List<uint16> offsets;

public static TransferLayout compute (Gee.Collection<Bytes> datagrams, size_t max_datagrams, size_t ndp_alignment,
size_t datagram_modulus, size_t datagram_remainder) {
size_t ndp_header_base_size = 4 + 2 + 2;
size_t ndp_entry_size = 2 + 2;
size_t ethernet_header_size = 14;

size_t ndp_header_offset = align (TRANSFER_HEADER_SIZE, ndp_alignment, 0);
size_t num_datagram_slots = size_t.min (datagrams.size, max_datagrams);
size_t ndp_header_size = ndp_header_base_size + ((num_datagram_slots + 1) * ndp_entry_size);

size_t current_transfer_size = ndp_header_offset + ndp_header_size;
var offsets = new Gee.ArrayList<uint16> ();

uint i = 0;
foreach (var datagram in datagrams) {
var size = (uint16) datagram.get_size ();

size_t start_offset =
align (current_transfer_size + ethernet_header_size, datagram_modulus, datagram_remainder);
size_t end_offset = start_offset + size;
if (end_offset > uint16.MAX)
break;

current_transfer_size = end_offset;
offsets.add ((uint16) start_offset);

i++;
if (i == max_datagrams)
break;
}

uint16 alignment_padding_value = 0;
return new TransferLayout () {
size = (uint16) current_transfer_size,
ndp_header_offset = (uint16) ndp_header_offset,
ndp_header_size = (uint16) ndp_header_size,
offsets = offsets,
};
}

var frame = new BufferBuilder (LITTLE_ENDIAN)
private static size_t align (size_t val, size_t modulus, size_t remainder) {
var delta = val % modulus;
if (delta != remainder)
return val + modulus - delta + remainder;
return val;
}
}

private static Bytes build_output_transfer (Gee.List<Bytes> datagrams, TransferLayout layout, uint16 sequence_number) {
var builder = new BufferBuilder (LITTLE_ENDIAN)
.append_string ("NCMH", StringTerminator.NONE)
.append_uint16 (transfer_header_length)
.append_uint16 (sequence)
.append_uint16 (block_length)
.append_uint16 (ndp_index)
.append_uint16 (TRANSFER_HEADER_SIZE)
.append_uint16 (sequence_number)
.append_uint16 (layout.size)
.append_uint16 (layout.ndp_header_offset);

uint16 next_ndp_index = 0;
builder
.seek (layout.ndp_header_offset)
.append_string ("NCM0", StringTerminator.NONE)
.append_uint16 (ndp_header_length)
.append_uint16 (next_ndp_index)
.append_uint16 (datagram_start_index)
.append_uint16 (datagram_length)
.append_uint16 (sentinel_start_index)
.append_uint16 (sentinel_size)
.append_uint16 (alignment_padding_value)
.append_bytes (datagram)
.build ();
.append_uint16 (layout.ndp_header_size)
.append_uint16 (next_ndp_index);

try {
yield device.bulk_transfer (config.tx_address, frame.get_data (), uint.MAX, io_cancellable);
} catch (GLib.Error e) {
int i;

i = 0;
foreach (var datagram in datagrams) {
builder
.append_uint16 (layout.offsets[i])
.append_uint16 ((uint16) datagram.get_size ());
i++;
}

i = 0;
foreach (var datagram in datagrams) {
builder
.seek (layout.offsets[i])
.append_bytes (datagram);
i++;
}

builder.seek (layout.size);

return builder.build ();
}

private static InetAddress? try_infer_remote_address_from_datagram (Bytes datagram) {
Expand All @@ -213,6 +338,7 @@ namespace Frida.Fruity {
}

internal class UsbNcmConfig {
public uint8 ctrl_iface;
public uint8 data_iface;
public int data_altsetting;
public uint8 rx_address;
Expand Down Expand Up @@ -256,6 +382,8 @@ namespace Frida.Fruity {
foreach (var setting in iface.altsetting) {
if (setting.bInterfaceClass == LibUSB.ClassCode.COMM &&
setting.bInterfaceSubClass == UsbCommSubclass.NCM) {
config.ctrl_iface = setting.bInterfaceNumber;

try {
parse_cdc_header (setting.extra, out config.mac_address_index);
found_cdc_header = true;
Expand Down

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