I'm trying to use the "mknod" call in C to create a clone of /dev/null. I am stumped as to the final parameter I should provide to "mknod()". I am supposed to give it a type dev_t, which specifies a major & minor number. I want to specify major 3, minor 1, but how can I do this?
dev_t seems to be a long long. It takes up 8 bytes, but I can't find anything about it. I've searched through quite a few /usr/include files, but I still can't find anything (nor on google).
If I 'stat()' /dev/null and then print the value of st_dev as an int (%d), I get '16'. But when I try and create a file called 'mynull', a clone of /dev/null, I get a major number of 0 and minor number of 16 , as shown below ( mknod() fails unless I call it as root ).
Code:
c--------- 1 root root 0, 16 Sep 18 21:20 mynull
From my man page:
Code:
If the file type is S_IFCHR or S_IFBLK then dev specifies the major and minor numbers of the newly created device special file; otherwise it is ignored.
Does anyone have any ideas as to how I can create a character special file with major number 1 and minor number 3?
Code:
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <strings.h>
#include <errno.h>
/* int mknod(const char *pathname, mode_t mode, dev_t dev); */
main( argc, argv )
int argc;
char *argv[];
{
int rc;
char path[256];
char errstr[1024];
strcpy( path, "mynull" );
rc = mknod( path, S_IFCHR, 16 );
if ( rc < 0 )
perror( "mknod" );
return(rc);
}
Here's what I get when I stat /dev/null:
Code:
rc = stat( "/dev/null" , &fstatus );
printf("dev_t for /dev/null = %d\n", fstatus.st_dev);
$ a.out
dev_t for /dev/null = 16
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