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嵌入式linux使用rpc实现多任务过程调用

易超
2023-12-01

在嵌入式linux应用产品开发过程中,由于应用程序使用了多进程开发模式,在软件平台为应用程序提供API接口时,会涉及到接口函数多任务调度支持的问题。

linux的每个进程有自己独立的地址空间,如果API接口函数在多个应用进程中执行,则不能使用全局变量进行数据存储,并且会涉及到很多临界资源保护和读写访问冲突等方面的问题。为了简化API接口函数的开发,并为应用程序提供简单的API接口函数,在API接口函数实现中,添加RPC机制实现多任务的本地过程调用,支持多进程模式的API接口函数支持。

RPC(Remote Procedure Call Protocol)的本意是一种远程过程调用机制,通过网络调用远程设备的过程函数。在Linux中,没有提供与RPC对应的本地过程调用机制,所以我们直接用RPC来进行本地的过程调用,实现对多任务应用开发的支持。

RPC的开发可以通过rpcgen工具实现,rpcgen可以自动生成RPC开发需要的大多数程序代码。rpcgen需要一个符合规格的说明文件作为输出,在给文件中可以定义API函数接口,数据结构等内容。rpcgen的说明文件示例如下:

program rpc_test{
        version VERSION{
                int rpc_test_get_status(void) = 1;
                int rpc_test_check(void) = 2;
                int rpc_test_set_val(int,int) = 3;
        } = 1;
} = 1;

说明文件编写完成后,可以使用rpcgen生成对应的程序代码,命令如下:

rm rpc_test_server.c 
rm rpc_test_client.c 
rpcgen -N -Sc -o rpc_test_client.c rpc_test.x
rpcgen -N -Ss -o rpc_test_server.c rpc_test.x
rpcgen -N rpc_test.x
arm-linux-gnueabihf-gcc -Wall -o rpc_server rpc_test_server.c rpc_test_svc.c rpc_test_xdr.c
arm-linux-gnueabihf-gcc -Wall -o rpc_client rpc_test_clnt.c rpc_test_client.c rpc_test_xdr.c

gcc -Wall -o rpc_server_x86 rpc_test_server.c rpc_test_svc.c rpc_test_xdr.c
gcc -Wall -o rpc_client_x86 rpc_test_clnt.c rpc_test_client.c rpc_test_xdr.c


RPC服务运行需要portmap服务支持,由于嵌入式系统中用来没有实现portmap机制,在执行rpc_server时,报错如下:

Cannot register service: RPC: Unable to receive; errno = Connection refused
unable to register (rpc_test, VERSION, udp).

下载portmap服务代码,编译生成portmap服务程序:

CC=arm-linux-gnueabihf-gcc ./configure --host=arm-linux 
下载portmap程序到开发板并执行,rpc_server可以正常启动。

下载rpc_client程序到开发板,执行时报错如下:

127.0.0.1: RPC: Unknown protocol
该错误是由于在/etc/下缺少配置文件protocols,创建文件,内容如下:

# Internet (IP) protocols
#
# Updated from http://www.iana.org/assignments/protocol-numbers and other
# sources.
# New protocols will be added on request if they have been officially
# assigned by IANA and are not historical.
# If you need a huge list of used numbers please install the nmap package.

ip      0       IP              # internet protocol, pseudo protocol number
#hopopt 0       HOPOPT          # IPv6 Hop-by-Hop Option [RFC1883]
icmp    1       ICMP            # internet control message protocol
igmp    2       IGMP            # Internet Group Management
ggp     3       GGP             # gateway-gateway protocol
ipencap 4       IP-ENCAP        # IP encapsulated in IP (officially ``IP'')
st      5       ST              # ST datagram mode
tcp     6       TCP             # transmission control protocol
egp     8       EGP             # exterior gateway protocol
igp     9       IGP             # any private interior gateway (Cisco)
pup     12      PUP             # PARC universal packet protocol
udp     17      UDP             # user datagram protocol
hmp     20      HMP             # host monitoring protocol
xns-idp 22      XNS-IDP         # Xerox NS IDP
rdp     27      RDP             # "reliable datagram" protocol
iso-tp4 29      ISO-TP4         # ISO Transport Protocol class 4 [RFC905]
dccp    33      DCCP            # Datagram Congestion Control Prot. [RFC4340]
xtp     36      XTP             # Xpress Transfer Protocol
ddp     37      DDP             # Datagram Delivery Protocol
idpr-cmtp 38    IDPR-CMTP       # IDPR Control Message Transport
ipv6    41      IPv6            # Internet Protocol, version 6
ipv6-route 43   IPv6-Route      # Routing Header for IPv6
ipv6-frag 44    IPv6-Frag       # Fragment Header for IPv6
idrp    45      IDRP            # Inter-Domain Routing Protocol
rsvp    46      RSVP            # Reservation Protocol
gre     47      GRE             # General Routing Encapsulation
esp     50      IPSEC-ESP       # Encap Security Payload [RFC2406]
ah      51      IPSEC-AH        # Authentication Header [RFC2402]
skip    57      SKIP            # SKIP
ipv6-icmp 58    IPv6-ICMP       # ICMP for IPv6
ipv6-nonxt 59   IPv6-NoNxt      # No Next Header for IPv6
ipv6-opts 60    IPv6-Opts       # Destination Options for IPv6
rspf    73      RSPF CPHB       # Radio Shortest Path First (officially CPHB)
vmtp    81      VMTP            # Versatile Message Transport
eigrp   88      EIGRP           # Enhanced Interior Routing Protocol (Cisco)
ospf    89      OSPFIGP         # Open Shortest Path First IGP
ax.25   93      AX.25           # AX.25 frames
ipip    94      IPIP            # IP-within-IP Encapsulation Protocol
etherip 97      ETHERIP         # Ethernet-within-IP Encapsulation [RFC3378]
encap   98      ENCAP           # Yet Another IP encapsulation [RFC1241]
#       99                      # any private encryption scheme
pim     103     PIM             # Protocol Independent Multicast
ipcomp  108     IPCOMP          # IP Payload Compression Protocol
vrrp    112     VRRP            # Virtual Router Redundancy Protocol [RFC5798]
l2tp    115     L2TP            # Layer Two Tunneling Protocol [RFC2661]
isis    124     ISIS            # IS-IS over IPv4
sctp    132     SCTP            # Stream Control Transmission Protocol
fc      133     FC              # Fibre Channel
mobility-header 135 Mobility-Header # Mobility Support for IPv6 [RFC3775]
udplite 136     UDPLite         # UDP-Lite [RFC3828]
mpls-in-ip 137  MPLS-in-IP      # MPLS-in-IP [RFC4023]
manet   138                     # MANET Protocols [RFC5498]
hip     139     HIP             # Host Identity Protocol
shim6   140     Shim6           # Shim6 Protocol [RFC5533]
wesp    141     WESP            # Wrapped Encapsulating Security Payload
rohc    142     ROHC            # Robust Header Compression


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