From owner-freebsd-current@FreeBSD.ORG  Thu Nov 28 11:17:59 2013
Return-Path: <owner-freebsd-current@FreeBSD.ORG>
Delivered-To: current@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115])
 (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id 9B5AD857
 for <current@freebsd.org>; Thu, 28 Nov 2013 11:17:59 +0000 (UTC)
Received: from mail-lb0-x235.google.com (mail-lb0-x235.google.com
 [IPv6:2a00:1450:4010:c04::235])
 (using TLSv1 with cipher ECDHE-RSA-RC4-SHA (128/128 bits))
 (No client certificate requested)
 by mx1.freebsd.org (Postfix) with ESMTPS id 26457175A
 for <current@freebsd.org>; Thu, 28 Nov 2013 11:17:58 +0000 (UTC)
Received: by mail-lb0-f181.google.com with SMTP id q8so6009195lbi.40
 for <current@freebsd.org>; Thu, 28 Nov 2013 03:17:57 -0800 (PST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113;
 h=mime-version:sender:date:message-id:subject:from:to:content-type;
 bh=SifdWtsMTFaSY1s4ytk9V8Z7r1diUauXug+cJoD8ExM=;
 b=gar26gckzSZG4bXGWgXJWSQWsX4KD9sPPXf9fa+dLEhanOJYepgYU7YdVvE4HGkgrG
 h9d+cR9hAGLcnETTtzfHE4Q8dvhg0FXeVLgWRPFUsp7kLrk8dyGeXxHtuoMEbfblB+uV
 uhgwXTyLgi/m1jttgs12RP0dhcvkPoDziJSTqHEnWubiKEo4JQ/yMkl6jLiyZjGxFbHm
 CL0auUB0iKuz+6XFnBpkAVp9N53iyfGArtAyFfgCUiaLBlR2uBA3cY+G6NcDy7IzIB0g
 TbPybxUrjyiCA8ujo5aWDghvFWoy/UpbDRca2KhgWFXbIpqtTostHl3xsE4dbyQk5QBR
 Qacw==
MIME-Version: 1.0
X-Received: by 10.112.141.166 with SMTP id rp6mr4236668lbb.39.1385637477048;
 Thu, 28 Nov 2013 03:17:57 -0800 (PST)
Sender: rizzo.unipi@gmail.com
Received: by 10.114.175.180 with HTTP; Thu, 28 Nov 2013 03:17:56 -0800 (PST)
Date: Thu, 28 Nov 2013 03:17:56 -0800
X-Google-Sender-Auth: LodEDk-nEqPYNMR49_7IMfW2_58
Message-ID: <CA+hQ2+iNurBQnmH-4-DN9V-krc_R=dbEaznJkxLDOzkJEWpFMg@mail.gmail.com>
Subject: [RFC] how to get the size of a malloc(9) block ?
From: Luigi Rizzo <rizzo@iet.unipi.it>
To: FreeBSD Current <current@freebsd.org>
Content-Type: text/plain; charset=ISO-8859-1
X-Content-Filtered-By: Mailman/MimeDel 2.1.16
X-BeenThere: freebsd-current@freebsd.org
X-Mailman-Version: 2.1.16
Precedence: list
List-Id: Discussions about the use of FreeBSD-current
 <freebsd-current.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-current>, 
 <mailto:freebsd-current-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-current/>
List-Post: <mailto:freebsd-current@freebsd.org>
List-Help: <mailto:freebsd-current-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-current>,
 <mailto:freebsd-current-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 28 Nov 2013 11:17:59 -0000

in porting some linux kernel code to FreeBSD we
stumbled upon ksize(), which returns the
actual size of a kmalloc() block.

We could easily implement it as the first part
of realloc(9) -- see kern/kern_malloc.c

Would it make sense to add this to the malloc(9) API ?
The userspace equivalent seems to be
malloc_usable_size(3) which according to the
manpage appeared in FreeBSD 7.0

cheers
luigi