From owner-freebsd-fs Fri Jun 8 19: 2:46 2001 Delivered-To: freebsd-fs@freebsd.org Received: from mass.dis.org (fumerola-laptop.corp.yahoo.com [216.145.60.111]) by hub.freebsd.org (Postfix) with ESMTP id AB5F537B401; Fri, 8 Jun 2001 19:02:41 -0700 (PDT) (envelope-from msmith@mass.dis.org) Received: from mass.dis.org (localhost [127.0.0.1]) by mass.dis.org (8.11.3/8.11.3) with ESMTP id f592Cjb02166; Fri, 8 Jun 2001 19:12:45 -0700 (PDT) (envelope-from msmith@mass.dis.org) Message-Id: <200106090212.f592Cjb02166@mass.dis.org> X-Mailer: exmh version 2.1.1 10/15/1999 To: Pat Dirks Cc: FreeBSD-Arch@freebsd.org, FreeBSD-FS@freebsd.org Subject: Re: Support for pivot_root-like system call? In-reply-to: Your message of "Fri, 08 Jun 2001 14:27:04 PDT." <200106082127.OAA23988@scv1.apple.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Fri, 08 Jun 2001 19:12:45 -0700 From: Mike Smith Sender: owner-freebsd-fs@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.org Just a couple of observations about this approach: - If you only replace the / mount, you only protect /. If an application traverses off / onto another filesystem during a lookup, the eventuating vnode is going to get the vfsops pointer for the filesystem handling the FS the lookup terminates on, circumventing the protection. A better approach will probably be to implement a 'mount template', where an FS can register a hook which allows it to decide whether if wants to be automagically layered over another FS being mounted, something like an automatic version of Terry's union mount. - There's an ugly tradeoff between kernel footprint and performance here. You want the checker in kernel space to avoid context switching and piping all your I/O to/from userspace, but if you're doing dictionary searches, that's stuff that is going to be sitting permanently mapped. 8( Hope this helps; thanks for raising the issue, it's an interesting one. 8) Regards, Mike -- ... every activity meets with opposition, everyone who acts has his rivals and unfortunately opponents also. But not because people want to be opponents, rather because the tasks and relationships force people to take different points of view. [Dr. Fritz Todt] V I C T O R Y N O T V E N G E A N C E To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-fs" in the body of the message