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#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <errno.h>
#include <string.h>
void error_handle( char * msg);
int main(int argc, char * argv[] )
{
int sock_tcp;
int sock_udp;
int option;
socklen_t length; // sys/types.h
sock_tcp = socket( PF_INET, SOCK_STREAM, 0 );
if( sock_tcp == -1 )
error_handle( "socket error()" );
sock_udp = socket( PF_INET, SOCK_DGRAM, 0 );
if( sock_udp == -1 )
error_handle( "scoket error()" );
length = sizeof( option );
if( getsockopt( sock_tcp, SOL_SOCKET, SO_SNDBUF, (void*) &option, &length ) == -1 )
error_handle( "getsockopt() error" );
printf( "tcp send buffer size : %d\n", option );
length = sizeof( option );
if( getsockopt( sock_tcp, SOL_SOCKET, SO_RCVBUF, (void*) &option, &length ) == -1 )
error_handle( "getsockopt() error" );
printf( "tcp receive buffer size : %d\n", option );
option = 1024 * 10;
if( setsockopt( sock_tcp, SOL_SOCKET, SO_SNDBUF, (void*) &option, sizeof( option ) ) == -1 )
error_handle( "setsockopt() error" );
length = sizeof( option );
option = 1024 * 20;
if( setsockopt( sock_tcp, SOL_SOCKET, SO_RCVBUF, (void*) &option, sizeof( option ) ) == -1 )
error_handle( "setsockopt() error" );
length = sizeof( option );
if( getsockopt( sock_tcp, SOL_SOCKET, SO_SNDBUF, (void*) &option, &length ) == -1 )
error_handle( "getsockopt() error" );
printf( "tcp send buffer size : %d\n", option );
length = sizeof( option );
if( getsockopt( sock_tcp, SOL_SOCKET, SO_RCVBUF, (void*) &option, &length ) == -1 )
error_handle( "getsockopt() error" );
printf( "tcp receive buffer size : %d\n", option );
/*
length = sizeof( option );
if( getsockopt( sock_udp, SOL_SOCKET, SO_SNDBUF, (void*) &option, &length ) == -1 )
error_handle( "getsockopt() error" );
printf( "udp send buffer size : %d\n", option );
length = sizeof( option );
if( getsockopt( sock_udp, SOL_SOCKET, SO_RCVBUF, (void*) &option, &length ) == -1 )
error_handle( "getsockopt() error" );
printf( "udp receive buffer size : %d\n", option );
*/
close (sock_tcp);
close (sock_udp);
return 0;
}
void error_handle( char * msg )
{
fprintf( stderr, "%s\n", msg );
fprintf( stderr, "errno number : %d\n", errno );
fprintf( stderr, "errno message: %s\n", strerror( errno ) );
exit(1);
}
| cs |
위 코드의 결과.
tcp send buffer size : 16384
tcp receive buffer size : 87380
tcp send buffer size : 20480
tcp receive buffer size : 40960
실제
setsockopt 의 변수로, 10240 을 주면 그의 2 배인 20480,
setsockopt 의 변수로, 20480 을 주면 그의 2 배인 40960
이 나온다.
왜 그런지 확인해 보려면,
man 7 socket
명령어를 linux 에서 실행시켜 보면,
아래와 같은 안내를 볼 수 있다.
SO_SNDBUF
Sets or gets the maximum socket send buffer in bytes. The kernel doubles this value (to allow space for
bookkeeping overhead) when it is set using setsockopt(2), and this doubled value is returned by getsock‐
opt(2). The default value is set by the /proc/sys/net/core/wmem_default file and the maximum allowed
value is set by the /proc/sys/net/core/wmem_max file. The minimum (doubled) value for this option is
2048.
