[LIP] Getting client credentials through a UNIX Domain Socket.

Hi all,

I  need a little help on getting client process' 
credentials on a Unix Domain Socket.I have been 
googling for the past few hours but have'nt been
able to locate a page with accurate info on how 
to get client credentials through UNIX Domains sockets
'on linux'.
Some of sites that have some info, refer to the 
SCM_CREDENTIALS control messages and recommend
going through the kernel source, which I did.


Now the code I wrote is a mix of what I read in 
UNPv1,Stevens and what I read on the web, but it
 doesn't work.

Please see the code below or the next paragraph for
 a brief on the problem.The code is longer than 
usual, please bear with me.

The problem I face is like this, when I try to get
client credentials on linux, I get a 'Resource 
temporarily unavailible' in recvmsg.The code returns
 thereafter.

When I comment out the return statements,
the execution continues after printing the error and
 the read calls that I make are able to read from the
socket descriptor(here in connfd) without any 
problems.


TIA,
Shehjar

===========CODE BELOW================
/* Some of the code is from UNPv1, Stevens. */
/* For getting client credentials. */
struct msghdr msg;
struct ucred cli_cred;

union {

struct cmsghdr cm;
char control[CMSG_SPACE(sizeof(struct ucred))];

} control_un;

        struct cmsghdr *cmptr;

        cmptr=NULL;
        msg.msg_control=control_un.control;
        msg.msg_controllen=sizeof(control_un.control);

        msg.msg_name=NULL;
        msg.msg_namelen=0;

        /* I don't want to read anything from the 
           socket except the credentials.
         */
        msg.msg_iov=NULL;
        msg.msg_iovlen=0;

        /* Getting credentials here. */
        if(recvmsg(connfd, &msg, 0)<0) {
                tmperr=errno;
                /* This is where I get a
                 * 'Resource temporarily unavailible'
                 */
                fprintf(log, "dl_run:Could not get
client");
                fprintf(log," credentials:%s\n",
strerror(tmperr));
                return -1;
        }

        if(msg.msg_controllen > sizeof(struct
cmsghdr)) {
                cmptr=CMSG_FIRSTHDR(&msg);
                if(cmptr->cmsg_len !=
CMSG_LEN(sizeof(struct
ucred))) {
                        fprintf(log, "dl_run:No client
credentials.\n");
                        return -1;
                }

                if(cmptr->cmsg_level!=SOL_SOCKET) {
                        fprintf(log, "dl_run:No client
credentials.\n");
                        return -1;
                }

                if(cmptr->cmsg_type!=SCM_CREDENTIALS)
{
                        fprintf(log, "dl_run:No client
credentials.\n");
                        return -1;
                }

                memcpy(&cli_cred, CMSG_DATA(cmptr),
sizeof(struct
ucred));
                
        }
        else {
                fprintf(log, "dl_run: No client
credentials.\n");
                return -1;
        }
        
=========================

Thanks again.



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