Procedure Remote Call
Outline
Concept of RPC SunRPC
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RPC Timeline
Client Server
Requ est
Blocked
Blocked Computing
Reply
Blocked
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RPC
There exists a way for processes to represent a task: procedure/function.
main() func(12); func() return 5; func(12); func() main() return 5;
Client
Server
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RPC
main() stub(12); stub Request Reply return 5;
Client
skeleton func(12); func() return 5;
Server
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Stubs
Stub is a function with the same interface as func(); it converts the function call into a network response and a network response into a function return. Skeleton converts requests into function calls and function returns into network replies. RPC System: used to generate both stub and skeleton (automatically).
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SunRPC
Widely used Remote Procedure Call system:
Sun Microsystems, implemented in most Unix systems NFS distributed file system is based on Sun RPC
Designed to call remote C procedures. Platform-independent.
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SunRPC Header Format
XID (transaction id) Server does not remember last XID it serviced Problem if client retransmits request while reply is in transit
0 XID MsgType = CALL (a) RPCVersion = 2 Program Version Procedure Credentials (variable) Verifier (variable) Data (b) 31 0 XID MsgType = REPLY Status = ACCEPTED Data 31
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RPC
One computer can be server for multiple procedures:
server may host several programs (identified by program number) each program may have several subsequent versions (version number) each version may contain one or more procedures (procedure number)
Program numbers are 32-bit hexadecimal values (0x21212100)
As user, you can choose any program number between 0x20000000 and 0x3FFFFFFF, but they have to be unique (not several programs with same number on same machine)
Version and procedure numbers are integers (1,2,...)
(prog, vers, proc)
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Sun RPC Program Numbers
FROM 0x00000000 0x20000000 0x40000000 0x60000000 0x80000000 0xa0000000 0xc0000000 0xe0000000 TO 0x1fffffff 0x3fffffff 0x5fffffff 0x7fffffff 0x9fffffff 0xbfffffff 0xdfffffff 0xffffffff VALUES ASSIGNED BY Sun Microsystems, Inc. System manager at a users site Transient (temporary) Reserved Reserved Reserved Reserved Reserved
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Sun RPC Program Numbers
NAME portmap rstatd rusersd nfs ypserv mountd dbxd ypbind ...
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NUMBER 100000 100001 100002 100003 100004 100005 100006 100007
DESCRIPTION port mapper rstat, rup, perfmeter remote users network file system yp (NIS) mount, showmount DMXprog (debugger) NIS binder
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Writing an RPC Program
client.c add_clnt.c add.h add.x add_xdr.c add_scv.c serverproc.c add_xdr.o add_svc.o serverproc.o server client.o add_clnt.o client
You obtain a client & server
You write these files
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rpcgen generates these files
You compile every C file
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Example
Step 1: Write a specification file (add.x)
struct add_in { /* Arguments of procedure */ long arg1; long arg2; }; typedef long add_out; /* Return value */ program ADD_PROG { version ADD_VERS { add_out ADD_PROC(add_in) = 1 /* Procedure# = 1 */ } = 1; /* Version# = 1 */ } = 0x3434000; /* Program# = 0x3434000 */
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Example
Contains specifications of:
add_in (arguments) typedef add_out (return values) program ADD_PROG (0x3434000) 1 version ADD_VERS (1) 1 procedure ADD_PROC (1)
Your procedures can only take ONE input argument and return ONE output return value (use structures for more):
more readable (structure entries should have meaningful names)
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Example
Step 2: generate stubs
rpcgen add.x
add.h contains declarations:
#define ADD_PROG 0x34340000 /* Program nb */ #define ADD_VERS 1 /* Version nb */ #define ADD_PROC 1 /* Procedure nb */ add_out * add_proc_1 (add_in *, CLIENT *); add_out * add_proc_1_svc (add_in *, struct svc_req *);
add_proc_1 is the stub (called client) by add_proc_1_svc is the actual procedure that you will write and run at the server
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Example
add_clnt.c: implementation of add_proc_1 add_svc.c: contains program which calls your procedure add_proc_1_svc when request received add_xdr.c: marshall/unmarshall routines
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Example
Step 3: write server procedure: serverproc.c
#include add.h add_out *add_proc_1_svc(add_in *in, struct svc_req *rqstp) { static add_out out; out = in->arg1 + in->arg2; return(&out); } rqstp contains some information about the requester (IP address, etc.)
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Example
Step 4: compile the server Need to compile together your procedure, the (generated) server program, the (generated) marshall/unmarshall procedures and the nsl library (contains the RPC runtime).
$ gcc -c serverproc.c $ gcc -c add_svc.c $ gcc -c add_xdr.c $ gcc -o server serverproc.o add_svc.o add_xdr.o -lnsl
To start the server:
./server
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Example
Step 5: write a client program client.c
#include add.h int main(int argc, char **argv) { CLIENT *cl; add_in in; add_out *out; if (argc!=4) {printf(Usage:...\n); return 1;} cl = clnt_create(argv[1], ADD_PROG, ADD_VERS, tcp); in.arg1 = atol(argv[2]); in.arg2 = atol(argv[3]); out = add_proc_1(&in, cl); if (out == NULL) {printf(Error: %s\n, clnt_sperror(cl, argv[1])); } else { printf{We received the result: %ld\n, * out); } clnt_destroy(cl); return 0; }
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Example
Create a client structure with clnt_create
#include <rpc/rpc.h> CLIENT *clnt_create(char *host, u_long prog, u_long vers, char *proto); host: name of server machine prog, vers: program/version number proto: transport protocol (tcp or udp)
You can call add_proc_1 to send the RPC When finished, destroy client structure (client structure can be used multiple times without being destroyed and recreated).
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Example
Step 6: compile the client
$ gcc -c client.c $ gcc -c add_clnt.c $ gcc -c add_xdr.c $ gcc -o client client.o add_clnt.o add_xdr.o -lnsl
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Example
Step 7: try it out
start your server: ./server send a request:
./client machine.cse.nd.edu 8 34 We received the result: 42
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Mutual Exclusion
Sun RPC: at most one remote procedure in a remote program can be invoked at a given time. Automatic mutual exclusion among...