Linux RPC

Comer Chapter 21(RPCgen Concept)

RFC 1057 – RPC Spec.UNIX Network Programming - Stevens

1

Using Remote Procedure Calls

• As a program specification technique• For program specification and as an

abstraction during design• Explicitly in the implementation• For design and implementation, from scratch• For design and implementation, with

standard libraries• For automated implementation

2

RPC Programming MechanismsONC (Open Network Computing)

• XDR library routines for data conversion• XDR library routines for complex data

structures• RPC run-time library routines• Program generator tool

3

RPC Programming Process

• Dividing the program into local and remote procedures.

4

Proc A

Client Stub

Server Stub

Proc B

RPC

RPC Dispatching(Procedure Location)

5

Proc A1

Client Stub

Server Stub

Proc B1

Proc A2

Client StubProc B2

Server Stub

Dispatcher

RPC

RPC

RPC Interface Specification

6

Proc A

Client comm

Server Iface

Proc B

Server Comm

Client Iface

RPC

RPCgen Input and Output

• Input– Q.x Interface specification file

• Output– Q.h Declarations header file– Q_xdr.cpp XDR procedure calls used to

marshal arguments– Q_clnt.cpp Client-side communications stub– Q_svc.cpp Server-side communications stub

7

RPC Process Flow

8

Q.x rpcgen

Q_clnt.cpp

Q.h

Q_xdr.cpp

Q_svc.cpp

Clientapplication

Clientinterface

Serverinterface

Remoteprocedures

Server

Clientcompile

compile

RPC General Build Procedure

9

Develop Interface

Develop Client Develop Server

Developing the Interface

10

MyApp.x

RPCgen

MyApp_clnt.cClient Stub

MyApp_svc.cServer Stub

MyApp.h

MyApp_xdr.c

Developing the Server

11

MyApp.x

RPCgen

MyApp_svc.cServer Stub

MyApp.hMySrvr.c MyApp_xdr.c

C Compiler

Linker

MySrvr.exe

Developing the Client

12

MyApp.idl

RPCgen

MyApp_clnt.cClient Stub

MyApp.hMyClnt.c

C Compiler

Linker

MyClnt.exe

MyApp_xdr.c

How the Server Prepares for a Connection

• (Be certain that Portmap is running)• Create UDP service• Register UDP service with Portmap• Create TCP service• Register TCP service with Portmap• Run service...– Uses select( ) to monitor ports.

13

Start Portmap

Portmap is included in all Linux distributions as a standard server.

Under Red Hat Fedora Open services applet ,select portmap and startFrom command line (as root)

/sbin/services portmap start

Other distributions should be similar

14

Server concurrency mode

RPC servers can be created in either single threaded or multi-threaded mode.

Servers automatically create and (when done) destroy a thread for each incoming connection.

15

Register the Server Program

svc_register(port#, SERV#, VER#, serv_func, proto#);

port#: port on which the service is activeSERV#: unique number for the serviceVER#: version for this particular serviceserv_func: name by which this function is calledproto#: IPPROTO_UDP or IPPROTO_TCP

16

How the Client Establishes a Connection

• Make a Remote Procedure Call• Find the Server Host Computer• Find Server Process Port # (through Portmap)• Create a (connection) to the Server Process

17

How the Client Establishes a Connection

clnt_create(server, SERV#, VER#, proto#);

remote procedure call...

Clnt_destroy(CLIENT);

18

Example #1

• Temperature Server (Fahrenheit to Centigrade)– Parameters passed as integers– TCP / IP port connection

• Source files:– temp.x– Tclient.c– tempServer.c

19

temp.x

program TEMPSERV {version TEMPVERS {

int TempConv(int) = 1; //procedure number} = 1; //version number

} = 77; //program number

20

TClient.c#include <stdio.h>, <stdlib.h>, <string.h>#include <rpc/rpc.h>#include "temp.h"#define YES 0#define NO 1

void main (int argc, char *argv[]){

int tempconvert(int temp, char *srvr);int temperature, nuTemp;int loopFlag;char srvr[25];CLIENT * cl;

21

TClient.c (cont)

strcpy (srvr, argv[1]);cl = clnt_create(srvr, TEMPSERV, TEMPVERS, "tcp");loopFlag = YES;

while(loopFlag == YES){

printf("Enter temperature in Faherenheit (-999 to quit)");

scanf ("%d", &temperature);ans = tempconv_1(&temperature, cl);

22

TClient.c (cont)

if (ans != NULL)nuTemp = * ans;

if (temperature == -999 || temperature == -9999){

loopFlag = NO;printf ("Goodbye...\n");continue;

}printf("That’s %2d in centigrade\n", nuTemp);

}clnt_destroy(cl);return 0;

}

23

tempServer.c

#include <stdlib.h>, <unistd.h>, <stdio.h>#include <rpc/rpc.h>, "temp.h"

static int count;static int nuTemp;

int *tempconv_1_svc (int *val, struct svc_req * rqst)

{int oldTemp;oldTemp = *val;

24

tempServer.c

if (oldTemp == -9999){

printf("We're shutting down...\n");exit (0);

}printf("We got a temperature of %d, ", oldTemp);count++;nuTemp = (int)((5*(oldTemp -32)) / 9.0);printf("and we returned a value of %d\n", nuTemp);sleep(1);return (&nuTemp);

}

25

Files created with rpcgen

• Input:– temp.x

• Output– temp.h– temp_xdr.c (NULL file)– temp_clnt.c– temp_svc.c

26

temp.h#include <rpc/rpc.h>

#ifdef __cplusplus

extern "C" {

#endif

#define TEMPSERV 77

#define TEMPVERS 1

#if defined(__STDC__) || defined(__cplusplus)

#define TempConv 1

extern int * tempconv_1(int *, CLIENT *);

extern int * tempconv_1_svc(int *, struct svc_req *);

extern int tempserv_1_freeresult (SVCXPRT *, xdrproc_t, caddr_t);

#ifdef __cplusplus}

#endif

#endif /* !_TEMP_H_RPCGEN */

27

temp_xdr.c

#include <rpc/rpc.h>

#include "temp.h"

28

temp_clnt.c#include <memory.h> /* for memset */#include "temp.h“/* Default timeout can be changed using

clnt_control() */

static struct timeval TIMEOUT = { 25, 0 };

int *tempconv_1(int *argp, CLIENT *clnt){static int clnt_res;memset((char *)&clnt_res, 0, sizeof(clnt_res));

29

temp_clnt.c (cont)

if (clnt_call (clnt, TempConv,(xdrproc_t) xdr_int, (caddr_t)

argp, (xdrproc_t) xdr_int, (caddr_t) &clnt_res,TIMEOUT) != RPC_SUCCESS)

{return (NULL);

}return (&clnt_res);}

30

temp_svc.c

#include "temp.h“#include <stdio.h>#include <stdlib.h>#include <rpc/pmap_clnt.h>#include <string.h>#include <memory.h>#include <sys/socket.h>#include <netinet/in.h>

#ifndef SIG_PF#define SIG_PF void(*)(int)#endif

31

temp_svc.c (cont)static void tempserv_1(struct svc_req *rqstp, register SVCXPRT *transp){

union {

int tempconv_1_arg;

} argument;

char *result;

xdrproc_t _xdr_argument, _xdr_result;

char *(*local)(char *, struct svc_req *);

switch (rqstp->rq_proc) {

case NULLPROC:

(void) svc_sendreply (transp, (xdrproc_t) xdr_void, (char *)NULL);return;

case TempConv:

_xdr_argument = (xdrproc_t) xdr_int;

_xdr_result = (xdrproc_t) xdr_int;

local = (char *(*)(char *, struct svc_req *)) tempconv_1_svc;break;

default:

svcerr_noproc (transp);

return; }32

temp_svc.c (cont)memset ((char *)&argument, 0, sizeof (argument));if (!svc_getargs (transp, (xdrproc_t) _xdr_argument,

(caddr_t) &argument)) {svcerr_decode (transp);return;

}result = (*local)((char *)&argument, rqstp);if (result != NULL && !svc_sendreply(transp, (xdrproc_t) _xdr_result, result)) {

svcerr_systemerr (transp);}if (!svc_freeargs (transp, (xdrproc_t) _xdr_argument, (caddr_t) &argument)) {

fprintf (stderr, "%s", "unable to free arguments");exit (1);

}return;

}

33

temp_svc.c (cont)int main (int argc, char **argv){

register SVCXPRT *transp;pmap_unset (TEMPSERV, TEMPVERS);transp = svcudp_create(RPC_ANYSOCK);if (transp == NULL) {

fprintf (stderr, "%s", "can’t create udp service."); exit(1);}if (!svc_register(transp, TEMPSERV, TEMPVERS,

tempserv_1, IPPROTO_UDP)) {fprintf (stderr, "%s", "unable to register

(TEMPSERV, TEMPVERS, udp).");exit(1);

}

34

temp_svc.c (cont)transp = svctcp_create(RPC_ANYSOCK, 0, 0);

if (transp == NULL) {fprintf (stderr, "%s", "cannot create

tcp service.");

exit(1);}if (!svc_register(transp, TEMPSERV, TEMPVERS,

tempserv_1, IPPROTO_TCP)) {fprintf (stderr, "%s", "unable to

register (TEMPSERV, TEMPVERS, tcp).");

exit(1);}svc_run ();fprintf (stderr, "%s", "svc_run returned");exit (1); /* NOTREACHED */}

35

Sample Client Output

D:\data\RPC\onrpc_temp\client\Debug>client localhost

Enter the temperature in Faherenheit (-999 to quit)32

That would be 0 in centigrade

Enter the temperature in Faherenheit (-999 to quit)100

That would be 37 in centigrade

Enter the temperature in Faherenheit (-999 to quit)212

That would be 100 in centigrade

Enter the temperature in Faherenheit (-999 to quit)-9999

Goodbye...

D:\data\RPC\onrpc_temp\client\Debug>

36

Sample Server Output

D:\data\RPC\examples\onrpc_temp\server\Debug>server

We got a temperature of 32, and we returned a value of 0

We got a temperature of 100, and we returned a value of 37

We got a temperature of 212, and we returned a value of 100

We're shutting down...

D:\data\RPC\examples\onrpc_temp\server\Debug>

37

Summary

• Linux RPC Implementation models SUN ONCRPC functionality

• RPC specific programming limited to linking original applications code with rpcgen interface code.

38