docs/87548: LIST_*, TAILQ_* man pages include memory leak in sample code

[John Baldwin]

The following reply was made to PR docs/87548; it has been noted by GNATS.

From: John Baldwin <jhb at freebsd.org>
To: freebsd-doc at freebsd.org
Cc: David Leppik <dleppik at vocalabs.com>,
 freebsd-gnats-submit at freebsd.org
Subject: Re: docs/87548: LIST_*, TAILQ_* man pages include memory leak in sample code
Date: Mon, 17 Oct 2005 13:53:11 -0400

 On Sunday 16 October 2005 05:50 pm, David Leppik wrote:
 > >Number:         87548
 > >Category:       docs
 > >Synopsis:       LIST_*, TAILQ_* man pages include memory leak in sample
 > > code Confidential:   no
 > >Severity:       non-critical
 > >Priority:       low
 > >Responsible:    freebsd-doc
 > >State:          open
 > >Quarter:
 > >Keywords:
 > >Date-Required:
 > >Class:          doc-bug
 > >Submitter-Id:   current-users
 > >Arrival-Date:   Sun Oct 16 22:00:27 GMT 2005
 > >Closed-Date:
 > >Last-Modified:
 > >Originator:     David Leppik
 > >Release:        None (old BSD code--see below)
 > >Organization:
 >
 > Vocal Laboratories
 >
 > >Environment:
 > >Description:
 >
 > I've seen this on Mac OS X and Linux, so this probably affects FreeBSD as
 > well.
 >
 > The man page for TAILQ_INSERT, TAILQ_REMOVE, etc. have the following sample
 > code:
 >
 > while (head.tqh_first != NULL)
 >              TAILQ_REMOVE(&head, head.tqh_first, entries);
 >
 > I was so shocked that I checked queue.h and sure enough, TAILQ_REMOVE does
 > not deallocate the queue entry (nor should it.)  The same is true for the
 > other structures mentioned in this man page.
 >
 > >How-To-Repeat:
 > >
 > >Fix:
 >
 > I'm just a lowly Java programmer, but I think the fix is:
 >
 > while (head.tqh_first != NULL) {
 >              np = head.tqh_first;
 >              TAILQ_REMOVE(&head, np, entries);
 >              free(np);
 > }
 >
 
 Well, it should be something like:
 
 	while (!TAILQ_EMPTY(&head)) {
 		np = TAILQ_FIRST(&head);
 		TAILQ_REMOVE(&head, np, entries);
 		free(np);
 	}
 
 And actually, on my machine here running current this is what the examples 
 look like:
                                              /* TailQ Deletion. */
      while (!TAILQ_EMPTY(&head)) {
              n1 = TAILQ_FIRST(&head);
              TAILQ_REMOVE(&head, n1, entries);
              free(n1);
      }
                                              /* Faster TailQ Deletion. */
      n1 = TAILQ_FIRST(&head);
      while (n1 != NULL) {
              n2 = TAILQ_NEXT(n1, entries);
              free(n1);
              n1 = n2;
      }
      TAILQ_INIT(&head);
 
 Which version of FreeBSD are you seeing the memory leak in?
 
 -- 
 John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
 "Power Users Use the Power to Serve"  =  http://www.FreeBSD.org