Generic name to handle and open by handle syscalls

The below set of patches implement open by handle support using exportfs
operations. This allows user space application to map a file name to file 
handle and later open the file using handle. This should be usable
for userspace NFS and 9P server. XFS already support this with the ioctls
XFS_IOC_PATH_TO_HANDLE and XFS_IOC_OPEN_BY_HANDLE.

Example program:
-------------
#include <stdio.h>
#include <stdlib.h>

#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

struct file_handle {
	int handle_size;
	int handle_type;
	void *f_handle;
};
int main(int argc, char *argv[])
{
	int ret;
	int fd;
	char buf[100];
	struct file_handle fh;
	fh.handle_type = 0;
	fh.handle = malloc(100);
	fh.handle_size = 100/sizeof(int);
	errno  = 0;
	ret = syscall(338, argv[1], &fh);
	if (ret) {
		perror("Error:");
		exit(1);
	}
	printf("%d\n",fh.handle_size);
	fd = syscall(339, &fh, O_RDONLY);
	if (fd <= 0 ) {
		perror("Error:");
		exit(1);
	}
	printf("fd = %d\n", fd);
	memset(buf, 0 , 100);
	while (read(fd, buf, 100) > 0) {
		printf("%s", buf);
		memset(buf, 0 , 100);
	}
	return 0;
}

-aneesh

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