[BusyBox] confused by copyfd.c

[Rainer Weikusat]

Paul Fox <pgf at brightstareng.com> writes:
> we run (mostly) busybox-1.00 on our product, and i just hit the
> problem where cp won't fail properly if a disk is full.

[...]

> looking at copyfd.c, i'm a little confused.  the routine in
> question is short, so i'll include it here:
>
> (note that it's possible that i'm hitting at least some of these
> errors because i've been building busybox with -O3 rather than
> the default -Os.)

Nope. While this is certainly unintentional, the code appears to
actually be C.

A mentally sane person would do this roughly like that:

static ssize_t copy_fd(int from, int to)
{
        char buf[4096];	/* pick whatever you like */
        ssize_t rc, total;

        total = 0;
        do {
        	rc = read(from, buf, sizeof(buf));
                
                if (rc > 0) {
                	total += rc;
                	rc = bb_full_write(to, buf, rc);
                }
        } while (rc > 0);

        return rc ? rc : total;
}        
[uncompiled/ may not be compatible]