On Thu, Apr 23, 2009 at 2:20 AM, Greg Freemyer <greg.freemyer@xxxxxxxxx> wrote:
> On Wed, Apr 22, 2009 at 3:38 PM, Rohit Sharma <imreckless@xxxxxxxxx> wrote:
>> Arun, i suggest that if you are using this for IPC then , better use pipes.
>>
>> And if you really want to use fd in another application then
>> pass the file descriptor to exec after doing a fork.
>>
>> something like this.
>>
>> in application_1
>>
>> ret = fork();
>>
>> if(ret == 0){
>> sprintf(buff, "%d", fd_1);
>> (void)exec("application_2","application_2", buff, (char*)0);
>> }
>>
>> .......
>> .........
>>
>> in application_2
>>
>> int fd_1;
>> sscanf(argv[1],"%d", &fd_1);
>>
>> read(fd_1, buff, BUFFSIZE);
>>
>> ....
>> .....
>>
>> I hope that helps.
>
> Decided to back and refresh my memory. I was not thinking of passing
> a FD via a pipe. I was thinking of doing it through sendmsg().
>
Well, this might incur some unnecessary overheads of sockets and their handlers.
The point is to simply pass the file descriptor across process.
I believe using sendmsg might be more useful if you have other needs to.
Else, IMO, using a simple fork and pipe should solve the issue easily.
A classical example.
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
int main(void)
{
int fd[2], nbytes;
pid_t childpid;
char string[] = "Hello, world!\n";
char readbuffer[80];
pipe(fd);
if((childpid = fork()) == -1)
{
perror("fork");
exit(1);
}
if(childpid == 0)
{
/* Child process closes up input side of pipe */
close(fd[0]);
/* Send "string" through the output side of pipe */
write(fd[1], string, (strlen(string)+1));
exit(0);
}
else
{
/* Parent process closes up output side of pipe */
close(fd[1]);
/* Read in a string from the pipe */
nbytes = read(fd[0], readbuffer, sizeof(readbuffer));
printf("Received string: %s", readbuffer);
}
return(0);
}
> I don't think I ever did that in Linux, so it may or may not work with
> a linux kernel.
>
> See http://archives.neohapsis.com/archives/postfix/2000-09/1476.html
> for a write-up of how it worked in at least some environments. I
> don't even remember what flavor of Unix I was using when I did the
> sendmsg() trick to pass a FD.
>
> Greg
> --
> Greg Freemyer
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--
Regards,
Sandeep.
“To learn is to change. Education is a process that changes the learner.”
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