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UDP4

UDP4协议说明

UDP的全称是User Datagram Protocol，它不提供复杂的控制机制，仅利用IP提供面向无连接的通信服务。它将上层应用程序发来的数据在收到的那一刻，立即按照原样发送到网络。

UDP报文格式：

各个参数说明如下：

字段	长度（字节）	描述
Source Port	2	发送端口，标识哪个应用程序发送（发送进程）。
Destination Port	2	目标端口，标识哪个应用程序接收（接收进程）。
Length	2	UDP首部加上UDP数据的字节数，最小为8。
Checksum	2	覆盖UDP首部和UDP数据，是可选的。
data octets	变长	UDP负载，可选的。

前面的四个参数对应到UEFI代码中就是UDP头部：

//
// UDP header definition
//
typedef struct {UINT16    SrcPort;UINT16    DstPort;UINT16    Length;UINT16    Checksum;
} EFI_UDP_HEADER;

UDP4代码综述

UDP4也是一个通用的网络协议，其实现在NetworkPkg\Udp4Dxe\Udp4Dxe.inf，这里首先需要看下它的入口：

EFI_STATUS
EFIAPI
Udp4DriverEntryPoint (IN EFI_HANDLE        ImageHandle,IN EFI_SYSTEM_TABLE  *SystemTable)
{//// Install the Udp4DriverBinding and Udp4ComponentName protocols.//Status = EfiLibInstallDriverBindingComponentName2 (ImageHandle,SystemTable,&gUdp4DriverBinding,ImageHandle,&gUdp4ComponentName,&gUdp4ComponentName2);if (!EFI_ERROR (Status)) {//// Initialize the UDP random port.//mUdp4RandomPort = (UINT16)(((UINT16)NetRandomInitSeed ()) % UDP4_PORT_KNOWN + UDP4_PORT_KNOWN); // 宏的值是1024}
}

因为UDP4也是一个UEFI Driver Model，所以第一步是安装gUdp4DriverBinding，其实现：

EFI_DRIVER_BINDING_PROTOCOL  gUdp4DriverBinding = {Udp4DriverBindingSupported,Udp4DriverBindingStart,Udp4DriverBindingStop,0xa,NULL,NULL
};

而第二步是初始化一个随机的UDP端口，根据通用网络协议的做法，UDP的端口占两个字节（即16位），只要不是0-1023里面的公认端口都可以，且跟TCP端口的一致也没有关系。

UDP4在UEFI网络协议栈中的关系图：

Udp4DriverBindingSupported

UDP4依赖于IP4：

EFI_STATUS
EFIAPI
Udp4DriverBindingSupported (IN EFI_DRIVER_BINDING_PROTOCOL  *This,IN EFI_HANDLE                   ControllerHandle,IN EFI_DEVICE_PATH_PROTOCOL     *RemainingDevicePath  OPTIONAL)
{//// Test for the Ip4 Protocol//Status = gBS->OpenProtocol (ControllerHandle,&gEfiIp4ServiceBindingProtocolGuid,NULL,This->DriverBindingHandle,ControllerHandle,EFI_OPEN_PROTOCOL_TEST_PROTOCOL);
}

Udp4DriverBindingStart

Start函数的流程大致如下：

1. 初始化UDP4_SERVICE_DATA。
2. 安装gEfiUdp4ServiceBindingProtocolGuid。

同其它驱动一样，重点也是结构体，这里就是UDP4_SERVICE_DATA。

UDP4_SERVICE_DATA

UDP4_SERVICE_DATA在Start函数中创建：

EFI_STATUS
EFIAPI
Udp4DriverBindingStart (IN EFI_DRIVER_BINDING_PROTOCOL  *This,IN EFI_HANDLE                   ControllerHandle,IN EFI_DEVICE_PATH_PROTOCOL     *RemainingDevicePath  OPTIONAL)
{Status = Udp4CreateService (Udp4Service, This->DriverBindingHandle, ControllerHandle);
}

其结构体定义如下：

typedef struct _UDP4_SERVICE_DATA_ {UINT32                          Signature;EFI_SERVICE_BINDING_PROTOCOL    ServiceBinding;EFI_HANDLE                      ImageHandle;EFI_HANDLE                      ControllerHandle;LIST_ENTRY                      ChildrenList;UINTN                           ChildrenNumber;IP_IO                           *IpIo;EFI_EVENT                       TimeoutEvent;
} UDP4_SERVICE_DATA;

相比之前的服务数据，这个结构体相当得简单，其中比较重要的成员有：

• ServiceBinding：对应mUdp4ServiceBinding：

EFI_SERVICE_BINDING_PROTOCOL  mUdp4ServiceBinding = {Udp4ServiceBindingCreateChild,Udp4ServiceBindingDestroyChild
};

用于创建UDP4子项。

• ChildrenList，ChildrenNumber：对应UDP4_INSTANCE_DATA结构体，由Udp4ServiceBindingCreateChild()创建，是表示子项的结构体，在UDP4_INSTANCE_DATA会进一步介绍。
• IpIo：它是对IP4实例的一个包装，UDP4通过它来进行通信，在IP_IO已经介绍过。在UDP4以及TCP4中会进场看到类似IP_IO这样的结构体，它们仅仅是对IP层的保证，之所以要有这样的包装，是因为存在IPv4和IPv6两个版本，而这里只关注IPv4。
• TimeoutEvent：一个定时事件，创建的位置是在Udp4CreateService()函数中：

EFI_STATUS
Udp4CreateService (IN OUT UDP4_SERVICE_DATA  *Udp4Service,IN     EFI_HANDLE         ImageHandle,IN     EFI_HANDLE         ControllerHandle)
{//// Create the event for Udp timeout checking.//Status = gBS->CreateEvent (EVT_TIMER | EVT_NOTIFY_SIGNAL,TPL_CALLBACK,Udp4CheckTimeout,Udp4Service,&Udp4Service->TimeoutEvent);//// Start the timeout timer event.//Status = gBS->SetTimer (Udp4Service->TimeoutEvent,TimerPeriodic,UDP4_TIMEOUT_INTERVAL // 50 milliseconds);

对应的回调函数Udp4CheckTimeout()，它用来检测接收到的报文是否过期，其主体代码：

VOID
EFIAPI
Udp4CheckTimeout (IN EFI_EVENT  Event,IN VOID       *Context)
{NET_LIST_FOR_EACH (Entry, &Udp4Service->ChildrenList) {//// Iterate all the instances belonging to this service context.//Instance = NET_LIST_USER_STRUCT (Entry, UDP4_INSTANCE_DATA, Link);NET_CHECK_SIGNATURE (Instance, UDP4_INSTANCE_DATA_SIGNATURE);if (!Instance->Configured || (Instance->ConfigData.ReceiveTimeout == 0)) {//// Skip this instance if it's not configured or no receive timeout.//continue;}NET_LIST_FOR_EACH_SAFE (WrapEntry, NextEntry, &Instance->RcvdDgramQue) {//// Iterate all the rxdatas belonging to this udp instance.//Wrap = NET_LIST_USER_STRUCT (WrapEntry, UDP4_RXDATA_WRAP, Link);//// TimeoutTick unit is microsecond, MNP_TIMEOUT_CHECK_INTERVAL unit is 100ns.//if (Wrap->TimeoutTick < (UDP4_TIMEOUT_INTERVAL / 10)) {//// Remove this RxData if it timeouts.//Udp4RecycleRxDataWrap (NULL, (VOID *)Wrap);} else {Wrap->TimeoutTick -= (UDP4_TIMEOUT_INTERVAL / 10);}}}
}

这里的Wrap对应结构体UDP4_RXDATA_WRAP：

typedef struct _UDP4_RXDATA_WRAP_ {LIST_ENTRY               Link;NET_BUF                  *Packet;UINT32                   TimeoutTick;EFI_UDP4_RECEIVE_DATA    RxData;
} UDP4_RXDATA_WRAP;

它通过Udp4WrapRxData()创建，然后放到一个队列中供UDP驱动处理，如果来不及处理就会过期，而过期时间也由这里的成员TimeoutTick指定，而该成员由另外的一个值指定：

Wrap->TimeoutTick = Instance->ConfigData.ReceiveTimeout;

Instance是后面会介绍的UDP4_INSTANCE_DATA中的配置参数ConfigData，ConfigData.ReceiveTimeout的值在创建时是-1，表示不会过期：

  //// use the -1 magic number to disable the receiving process of the ip instance.//Ip4ConfigData->ReceiveTimeout = (UINT32)(-1);

不过在UDP4的配置中可以修改：

EFI_STATUS
EFIAPI
Udp4Configure (IN EFI_UDP4_PROTOCOL     *This,IN EFI_UDP4_CONFIG_DATA  *UdpConfigData OPTIONAL)
{if (UdpConfigData != NULL) {if (Instance->Configured) {//// Save the reconfigurable parameters.//Instance->ConfigData.TransmitTimeout = UdpConfigData->TransmitTimeout;}}
}

UDP4_INSTANCE_DATA

UDP4_INSTANCE_DATA表示一个UDP4子项，其它位于NetworkPkg\Udp4Dxe\Udp4Impl.h：

typedef struct _UDP4_INSTANCE_DATA_ {UINT32                  Signature;LIST_ENTRY              Link;UDP4_SERVICE_DATA       *Udp4Service;EFI_UDP4_PROTOCOL       Udp4Proto;EFI_UDP4_CONFIG_DATA    ConfigData;EFI_HANDLE              ChildHandle;BOOLEAN                 Configured;BOOLEAN                 IsNoMapping;NET_MAP                 TxTokens;NET_MAP                 RxTokens;NET_MAP                 McastIps;LIST_ENTRY              RcvdDgramQue;LIST_ENTRY              DeliveredDgramQue;UINT16                  HeadSum;EFI_STATUS              IcmpError;IP_IO_IP_INFO           *IpInfo;BOOLEAN                 InDestroy;
} UDP4_INSTANCE_DATA;

下面介绍其中比较重要的成员：

• Udp4Service：指向UDP4服务的结构体。

• Udp4Proto：对应EFI_UDP4_PROTOCOL，后面会进一步介绍。

• ConfigData：UDP配置数据：

typedef struct {//// Receiving Filters//BOOLEAN             AcceptBroadcast;BOOLEAN             AcceptPromiscuous;BOOLEAN             AcceptAnyPort;BOOLEAN             AllowDuplicatePort;//// I/O parameters//UINT8               TypeOfService;UINT8               TimeToLive;BOOLEAN             DoNotFragment;UINT32              ReceiveTimeout;UINT32              TransmitTimeout;//// Access Point//BOOLEAN             UseDefaultAddress;EFI_IPv4_ADDRESS    StationAddress;EFI_IPv4_ADDRESS    SubnetMask;UINT16              StationPort;EFI_IPv4_ADDRESS    RemoteAddress;UINT16              RemotePort;
} EFI_UDP4_CONFIG_DATA;

• TxTokens、RxTokens：描述收发数据的映射：

typedef struct {LIST_ENTRY    Used;LIST_ENTRY    Recycled;UINTN         Count;
} NET_MAP;

真正的Token是EFI_UDP4_COMPLETION_TOKEN：

typedef struct {EFI_EVENT     Event;EFI_STATUS    Status;union {EFI_UDP4_RECEIVE_DATA     *RxData;EFI_UDP4_TRANSMIT_DATA    *TxData;} Packet;
} EFI_UDP4_COMPLETION_TOKEN;

• RcvdDgramQue、DeliveredDgramQue：处理收发数据的队列。
• IpInfo：底层IP4实例需要使用到的结构体：

///
/// The IP_IO_IP_INFO is used in IpIoSend() to override the default IP instance
/// in IP_IO.
///
typedef struct _IP_IO_IP_INFO {EFI_IP_ADDRESS               Addr;IP_IO_IP_MASK                PreMask;LIST_ENTRY                   Entry;EFI_HANDLE                   ChildHandle;IP_IO_IP_PROTOCOL            Ip;IP_IO_IP_COMPLETION_TOKEN    DummyRcvToken;INTN                         RefCnt;UINT8                        IpVersion;
} IP_IO_IP_INFO;

从注释中可以看到发送数据时会使用到。

EFI_UDP4_PROTOCOL

UDP4通信的接口，该Protocol的结构体如下：

///
/// The EFI_UDP4_PROTOCOL defines an EFI UDPv4 Protocol session that can be used
/// by any network drivers, applications, or daemons to transmit or receive UDP packets.
/// This protocol instance can either be bound to a specified port as a service or
/// connected to some remote peer as an active client. Each instance has its own settings,
/// such as the routing table and group table, which are independent from each other.
///
struct _EFI_UDP4_PROTOCOL {EFI_UDP4_GET_MODE_DATA    GetModeData;EFI_UDP4_CONFIGURE        Configure;EFI_UDP4_GROUPS           Groups;EFI_UDP4_ROUTES           Routes;EFI_UDP4_TRANSMIT         Transmit;EFI_UDP4_RECEIVE          Receive;EFI_UDP4_CANCEL           Cancel;EFI_UDP4_POLL             Poll;
};

对应的实现：

EFI_UDP4_PROTOCOL  mUdp4Protocol = {Udp4GetModeData,Udp4Configure,Udp4Groups,Udp4Routes,Udp4Transmit,Udp4Receive,Udp4Cancel,Udp4Poll
};

后面会介绍这些函数的实现。

Udp4.GetModeData

对应的实现是Udp4GetModeData()，其代码实现：

EFI_STATUS
EFIAPI
Udp4GetModeData (IN  EFI_UDP4_PROTOCOL                *This,OUT EFI_UDP4_CONFIG_DATA             *Udp4ConfigData OPTIONAL,OUT EFI_IP4_MODE_DATA                *Ip4ModeData    OPTIONAL,OUT EFI_MANAGED_NETWORK_CONFIG_DATA  *MnpConfigData  OPTIONAL,OUT EFI_SIMPLE_NETWORK_MODE          *SnpModeData    OPTIONAL)
{if (Udp4ConfigData != NULL) {//// Set the Udp4ConfigData.//CopyMem (Udp4ConfigData, &Instance->ConfigData, sizeof (*Udp4ConfigData));}Ip = Instance->IpInfo->Ip.Ip4;//// Get the underlying Ip4ModeData, MnpConfigData and SnpModeData.//Status = Ip->GetModeData (Ip, Ip4ModeData, MnpConfigData, SnpModeData);}

从这里可以看出，上层的网络协议可以获取到下层所有的模式数据。

对于UDP4来说，数据在UDP4_INSTANCE_DATA的ConfigData成员中。

Udp4.Configure

对应的实现是Udp4Configure()，其代码实现：

EFI_STATUS
EFIAPI
Udp4Configure (IN EFI_UDP4_PROTOCOL     *This,IN EFI_UDP4_CONFIG_DATA  *UdpConfigData OPTIONAL)
{// 根据是否有配置存在两种情况，没有数据相当于重置if (UdpConfigData != NULL) {if (Instance->Configured) {//// The instance is already configured, try to do the re-configuration.//if (!Udp4IsReconfigurable (&Instance->ConfigData, UdpConfigData)) {//// If the new configuration data wants to change some unreconfigurable// settings, return EFI_ALREADY_STARTED.//Status = EFI_ALREADY_STARTED;goto ON_EXIT;}//// Save the reconfigurable parameters.//Instance->ConfigData.TypeOfService   = UdpConfigData->TypeOfService;Instance->ConfigData.TimeToLive      = UdpConfigData->TimeToLive;Instance->ConfigData.DoNotFragment   = UdpConfigData->DoNotFragment;Instance->ConfigData.ReceiveTimeout  = UdpConfigData->ReceiveTimeout;Instance->ConfigData.TransmitTimeout = UdpConfigData->TransmitTimeout;} else {//// Construct the Ip configuration data from the UdpConfigData.//Udp4BuildIp4ConfigData (UdpConfigData, &Ip4ConfigData);//// Configure the Ip instance wrapped in the IpInfo.//Status = IpIoConfigIp (Instance->IpInfo, &Ip4ConfigData);if (EFI_ERROR (Status)) {if (Status == EFI_NO_MAPPING) {Instance->IsNoMapping = TRUE;}goto ON_EXIT;}Instance->IsNoMapping = FALSE;//// Save the configuration data.//CopyMem (&Instance->ConfigData, UdpConfigData, sizeof (Instance->ConfigData));IP4_COPY_ADDRESS (&Instance->ConfigData.StationAddress, &Ip4ConfigData.StationAddress);IP4_COPY_ADDRESS (&Instance->ConfigData.SubnetMask, &Ip4ConfigData.SubnetMask);//// Try to allocate the required port resource.//Status = Udp4Bind (&Udp4Service->ChildrenList, &Instance->ConfigData);if (EFI_ERROR (Status)) {//// Reset the ip instance if bind fails.//IpIoConfigIp (Instance->IpInfo, NULL);goto ON_EXIT;}//// Pre calculate the checksum for the pseudo head, ignore the UDP length first.//CopyMem (&LocalAddr, &Instance->ConfigData.StationAddress, sizeof (IP4_ADDR));CopyMem (&RemoteAddr, &Instance->ConfigData.RemoteAddress, sizeof (IP4_ADDR));Instance->HeadSum = NetPseudoHeadChecksum (LocalAddr,RemoteAddr,EFI_IP_PROTO_UDP,0);Instance->Configured = TRUE;}} else {//// UdpConfigData is NULL, reset the instance.//Instance->Configured  = FALSE;Instance->IsNoMapping = FALSE;//// Reset the Ip instance wrapped in the IpInfo.//IpIoConfigIp (Instance->IpInfo, NULL);//// Cancel all the user tokens.//Instance->Udp4Proto.Cancel (&Instance->Udp4Proto, NULL);//// Remove the buffered RxData for this instance.//Udp4FlushRcvdDgram (Instance);}
}

根据输入参数的不同，以及是否已经配置过，会走到不同的流程，此外，UDP4还会配置进一步调用IP4的接口进行配置。

Udp4.Transmit

对应的实现是Udp4Transmit()，其代码实现：

EFI_STATUS
EFIAPI
Udp4Transmit (IN EFI_UDP4_PROTOCOL          *This,IN EFI_UDP4_COMPLETION_TOKEN  *Token)
{//// Validate the Token, if the token is invalid return the error code.//Status = Udp4ValidateTxToken (Instance, Token);if (EFI_ERROR (Status)) {goto ON_EXIT;}if (EFI_ERROR (NetMapIterate (&Instance->TxTokens, Udp4TokenExist, Token)) ||EFI_ERROR (NetMapIterate (&Instance->RxTokens, Udp4TokenExist, Token))){//// Try to find a duplicate token in the two token maps, if found, return// EFI_ACCESS_DENIED.//Status = EFI_ACCESS_DENIED;goto ON_EXIT;}TxData = Token->Packet.TxData;//// Create a net buffer to hold the user buffer and the udp header.//Packet = NetbufFromExt ((NET_FRAGMENT *)TxData->FragmentTable,TxData->FragmentCount,UDP4_HEADER_SIZE,0,Udp4NetVectorExtFree,NULL);if (Packet == NULL) {Status = EFI_OUT_OF_RESOURCES;goto ON_EXIT;}//// Store the IpIo in ProtoData.//Udp4Service                       = Instance->Udp4Service;*((UINTN *)&Packet->ProtoData[0]) = (UINTN)(Udp4Service->IpIo);Udp4Header = (EFI_UDP_HEADER *)NetbufAllocSpace (Packet, UDP4_HEADER_SIZE, TRUE);ASSERT (Udp4Header != NULL);ConfigData = &Instance->ConfigData;//// Fill the udp header.//Udp4Header->SrcPort  = HTONS (ConfigData->StationPort);Udp4Header->DstPort  = HTONS (ConfigData->RemotePort);Udp4Header->Length   = HTONS ((UINT16)Packet->TotalSize);Udp4Header->Checksum = 0;UdpSessionData = TxData->UdpSessionData;IP4_COPY_ADDRESS (&Override.Ip4OverrideData.SourceAddress, &ConfigData->StationAddress);if (UdpSessionData != NULL) {//// Set the SourceAddress, SrcPort and Destination according to the specified// UdpSessionData.//if (!EFI_IP4_EQUAL (&UdpSessionData->SourceAddress, &mZeroIp4Addr)) {IP4_COPY_ADDRESS (&Override.Ip4OverrideData.SourceAddress, &UdpSessionData->SourceAddress);}if (UdpSessionData->SourcePort != 0) {Udp4Header->SrcPort = HTONS (UdpSessionData->SourcePort);}if (UdpSessionData->DestinationPort != 0) {Udp4Header->DstPort = HTONS (UdpSessionData->DestinationPort);}CopyMem (&Source, &Override.Ip4OverrideData.SourceAddress, sizeof (IP4_ADDR));CopyMem (&Destination, &UdpSessionData->DestinationAddress, sizeof (IP4_ADDR));//// calculate the pseudo head checksum using the overridden parameters.//HeadSum = NetPseudoHeadChecksum (Source,Destination,EFI_IP_PROTO_UDP,0);} else {//// UdpSessionData is NULL, use the address and port information previously configured.//CopyMem (&Destination, &ConfigData->RemoteAddress, sizeof (IP4_ADDR));HeadSum = Instance->HeadSum;}//// calculate the checksum.//Udp4Header->Checksum = Udp4Checksum (Packet, HeadSum);if (Udp4Header->Checksum == 0) {//// If the calculated checksum is 0, fill the Checksum field with all ones.//Udp4Header->Checksum = 0xffff;}//// Fill the IpIo Override data.//if (TxData->GatewayAddress != NULL) {IP4_COPY_ADDRESS (&Override.Ip4OverrideData.GatewayAddress, TxData->GatewayAddress);} else {ZeroMem (&Override.Ip4OverrideData.GatewayAddress, sizeof (EFI_IPv4_ADDRESS));}Override.Ip4OverrideData.Protocol      = EFI_IP_PROTO_UDP;Override.Ip4OverrideData.TypeOfService = ConfigData->TypeOfService;Override.Ip4OverrideData.TimeToLive    = ConfigData->TimeToLive;Override.Ip4OverrideData.DoNotFragment = ConfigData->DoNotFragment;//// Save the token into the TxToken map.//Status = NetMapInsertTail (&Instance->TxTokens, Token, Packet);//// Send out this datagram through IpIo.//IpDestAddr.Addr[0] = Destination;Status             = IpIoSend (Udp4Service->IpIo,Packet,Instance->IpInfo,Instance,Token,&IpDestAddr,&Override);
}

Udp4.Receive

对应的实现是Udp4Receive()，其代码实现：

EFI_STATUS
EFIAPI
Udp4Receive (IN EFI_UDP4_PROTOCOL          *This,IN EFI_UDP4_COMPLETION_TOKEN  *Token)
{if (EFI_ERROR (NetMapIterate (&Instance->RxTokens, Udp4TokenExist, Token)) ||EFI_ERROR (NetMapIterate (&Instance->TxTokens, Udp4TokenExist, Token))){//// Return EFI_ACCESS_DENIED if the specified token is already in the TxTokens or// RxTokens map.//Status = EFI_ACCESS_DENIED;goto ON_EXIT;}Token->Packet.RxData = NULL;//// Save the token into the RxTokens map.//Status = NetMapInsertTail (&Instance->RxTokens, Token, NULL);if (EFI_ERROR (Status)) {Status = EFI_NOT_READY;goto ON_EXIT;}//// If there is an icmp error, report it.//Udp4ReportIcmpError (Instance);//// Try to deliver the received datagrams.//Udp4InstanceDeliverDgram (Instance);//// Dispatch the DPC queued by the NotifyFunction of Token->Event.//DispatchDpc ();
}

同其它的网络协议中的Receive一样，重点是注册Token。

Udp4.Poll

对应的实现是Udp4Poll()，其代码实现就是调用下一层的Poll：

EFI_STATUS
EFIAPI
Udp4Poll (IN EFI_UDP4_PROTOCOL  *This)
{Ip       = Instance->IpInfo->Ip.Ip4;//// Invode the Ip instance consumed by the udp instance to do the poll operation.//return Ip->Poll (Ip);
}

代码示例

DHCP和DNS等都是使用UDP的，后面会进一步说明。