Not enough queuing of datagrams on a unix domain socket

[shotgunlee]

Not enough queuing of datagrams on a unix domain socket

When I test in Linux 2.4.18-14debug(Redhat 8.0), only 10 or 11 datagrams can be queued on a unix domain socket(SOCK_DGRAM)'s receive buffer. If a sender tries to send more datagrams, it blocks(in a blocking sento) or returns error(in a non-blocking sendto). That doesn't make sense, because each message is 10 bytes long and receive buffer size is 64KB. Is there any solution?

----> dg_serv.c
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>

#define MAXLINE 1024

int
main(int argc, char **argv)
{
int sockfd, clilen, rcvbufsize, len;
struct sockaddr_un cliaddr, servaddr;
char recvline[MAXLINE + 1];

char UNIXDG_PATH[30]="unix_sock_dgram";

sockfd = socket(AF_LOCAL, SOCK_DGRAM, 0);

unlink(UNIXDG_PATH);
bzero(&servaddr, sizeof(servaddr));
servaddr.sun_family = AF_LOCAL;
strcpy(servaddr.sun_path, UNIXDG_PATH);

bind(sockfd, (struct sockaddr*) &servaddr, sizeof(servaddr));
len = sizeof(rcvbufsize);
getsockopt( sockfd, SOL_SOCKET, SO_RCVBUF, &rcvbufsize, &len);
printf("recv buffer size = %d\n", rcvbufsize);

clilen = sizeof(cliaddr);
while (1) {
int n;

getchar();

while( (n = recvfrom(sockfd, recvline, MAXLINE, MSG_DONTWAIT, (struct sockaddr*) &cliaddr, &clilen ))>0 ) {
recvline[n]='\0';

printf("Received :%s", recvline);
}

}
}

----> dg_cli.c
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <errno.h>

#define MAXLINE 1024

int
main(int argc, char **argv)
{
int sockfd, count=0;
struct sockaddr_un cliaddr, servaddr;

char UNIXDG_PATH[30]="unix_sock_dgram";

sockfd = socket(AF_LOCAL, SOCK_DGRAM, 0);

bzero(&cliaddr, sizeof(cliaddr)); /* bind an address for us */
cliaddr.sun_family = AF_LOCAL;
strcpy(cliaddr.sun_path, tmpnam(NULL));

bind(sockfd, (struct sockaddr*) &cliaddr, sizeof(cliaddr));

bzero(&servaddr, sizeof(servaddr)); /* fill in server's address */
servaddr.sun_family = AF_LOCAL;
strcpy(servaddr.sun_path, UNIXDG_PATH);


while (1) {
char sendline[MAXLINE];
int retval;

sprintf( sendline, "Message %d\n" , count);


retval = sendto(sockfd, sendline, strlen(sendline), MSG_DONTWAIT, (struct sockaddr*) &servaddr, sizeof(servaddr) );

printf("called sendto() with %s", sendline);
printf("return value = %d, errno = %d\n", retval,errno);

sleep(1);


count += 1;

}
}

[shotgunlee]

I found a solution... sysctl -w net.unix.max_dgram_qlen=200