Another class of problem

(Well, it looks like someone cleaned up a possible defect in the
delete_slaves method in 	 ruby/ext/tk/tcltklib.c without my bringing
it up.   Cool!)

Here's another kind of error pointed out by coverity:

Checker: FORWARD_NULL (help)
File: ruby/io.c
Function: io_fwrite
Description: Variable "(fptr)->wbuf" tracked as NULL was passed to a
function that dereferences it.




540  	/* writing functions */
541  	static long
542  	io_fwrite(VALUE str, OpenFile *fptr)
543  	{
544  	    long len, n, r, l, offset = 0;
545  	
546  	    len = RSTRING(str)->len;
547  	    if ((n = len) <= 0) return n;

Event var_compare_op: Added "(fptr)->wbuf" due to comparison "(fptr)->wbuf == 0"
Also see events: [var_deref_model]
At conditional (1): "(fptr)->wbuf == 0" taking true path
At conditional (2): "(fptr)->mode & 8 == 0" taking false path

548  	    if (fptr->wbuf == NULL && !(fptr->mode & FMODE_SYNC)) {
549  	        fptr->wbuf_off = 0;
550  	        fptr->wbuf_len = 0;
551  	        fptr->wbuf_capa = 8192;
552  	        fptr->wbuf = ALLOC_N(char, fptr->wbuf_capa);
553  	    }

At conditional (3): "(fptr)->mode & 8 != 0" taking true path

554  	    if ((fptr->mode & FMODE_SYNC) ||
555  	        (fptr->wbuf && fptr->wbuf_capa <= fptr->wbuf_len + len) ||
556  	        ((fptr->mode & FMODE_TTY) &&
memchr(RSTRING(str)->ptr+offset, '\n', len))) {
557  	        /* xxx: use writev to avoid double write if available */

At conditional (4): "(fptr)->wbuf_len != 0" taking true path
At conditional (5): "((fptr)->wbuf_len + len) <= (fptr)->wbuf_capa"
taking true path

558  	        if (fptr->wbuf_len && fptr->wbuf_len+len <= fptr->wbuf_capa) {

At conditional (6): "(fptr)->wbuf_capa < (((fptr)->wbuf_off +
(fptr)->wbuf_len) + len)" taking true path

559  	            if (fptr->wbuf_capa < fptr->wbuf_off+fptr->wbuf_len+len) {

Event var_deref_model: Variable "(fptr)->wbuf" tracked as NULL was
passed to a function that dereferences it.
Also see events: [var_compare_op]

560  	                MEMMOVE(fptr->wbuf, fptr->wbuf+fptr->wbuf_off,
char, fptr->wbuf_len);
561  	                fptr->wbuf_off = 0;
562  	            }
563  	            MEMMOVE(fptr->wbuf+fptr->wbuf_off+fptr->wbuf_len,
RSTRING(str)->ptr+offset, char, len);
564  	            fptr->wbuf_len += len;
565  	            n = 0;
566  	        }
567  	        if (io_fflush(fptr) < 0)
568  	            return -1L;
569  	        if (n == 0)
570  	            return len;
571  	        /* avoid context switch between "a" and "\n" in STDERR.puts "a".
572  	           [ruby-dev:25080] */
573  		if (fptr->stdio_file != stderr && !rb_thread_fd_writable(fptr->fd)) {
574  		    rb_io_check_closed(fptr);
575  		}
576  	      retry:
577  	        l = n;
578  	        if (PIPE_BUF < l &&
579  	            !rb_thread_critical &&
580  	            !rb_thread_alone() &&
581  	            wsplit_p(fptr)) {
582  	            l = PIPE_BUF;
583  	        }
584  	        TRAP_BEG;
585  		r = write(fptr->fd, RSTRING(str)->ptr+offset, l);
586  	        TRAP_END; /* xxx: signal handler may modify given string. */
587  	        if (r == n) return len;
588  	        if (0 <= r) {
589  	            offset += r;
590  	            n -= r;
591  	            errno = EAGAIN;
592  	        }
593  	        if (rb_io_wait_writable(fptr->fd)) {
594  	            rb_io_check_closed(fptr);
595  		    if (offset < RSTRING(str)->len)
596  			goto retry;
597  	        }
598  	        return -1L;
599  	    }
600  	
601  	    if (fptr->wbuf_off) {
602  	        if (fptr->wbuf_len)
603  	            MEMMOVE(fptr->wbuf, fptr->wbuf+fptr->wbuf_off, char,
fptr->wbuf_len);
604  	        fptr->wbuf_off = 0;
605  	    }
606  	    MEMMOVE(fptr->wbuf+fptr->wbuf_off+fptr->wbuf_len,
RSTRING(str)->ptr+offset, char, len);
607  	    fptr->wbuf_len += len;
608  	    return len;
609  	}