Cloning filedescriptor

[Michal Ludvig <michal-list@xxxxxxxx>]

Hi all,

I'm trying to port some kernel code from OpenBSD to Linux and need an
advice ;-) The intent is to "clone" a filedescriptor but let the result
have different "file_operations" (f_op). With the BSD semantics it is
done in a ioctl() on a given device:

	fd = open("/dev/something", ...);
	ioctl(fd, CRIOGET, &cfd);

Now 'fd' uses the original f_op and 'cfd' the new ones.

So I did an ioctl handler for the device and let it handle CRIOGET:

        case CRIOGET:
                fd = get_unused_fd();
                new_file = get_empty_filp();
                memcpy(new_file, file, sizeof(struct file));
                new_file->f_op = &new_fops;
                fd_install(fd, new_file);
                put_user(fd, (int*)arg);
                return 0;

This works but I bet it is not very clean. Especially the memcpy()
copying (possible) locks, refcounts, ...

Is there a better way to "cleanly" duplicate "struct file" and attach it
to a new filedescriptor?

Thanks!

Michal Ludvig

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