From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48014) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b5ApU-0004Jz-Mv for qemu-devel@nongnu.org; Tue, 24 May 2016 07:48:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b5ApT-0002zC-Kl for qemu-devel@nongnu.org; Tue, 24 May 2016 07:48:56 -0400 Date: Tue, 24 May 2016 12:48:45 +0100 From: "Richard W.M. Jones" Message-ID: <20160524114845.GF28935@redhat.com> References: <1463470536-8981-1-git-send-email-famz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1463470536-8981-1-git-send-email-famz@redhat.com> Subject: Re: [Qemu-devel] [PATCH v5 00/27] block: Lock images when opening List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Fam Zheng Cc: qemu-devel@nongnu.org, Kevin Wolf , qemu-block@nongnu.org, Jeff Cody , Markus Armbruster , Max Reitz , stefanha@redhat.com, den@openvz.org, pbonzini@redhat.com, John Snow On Tue, May 17, 2016 at 03:35:09PM +0800, Fam Zheng wrote: > v5: - Change "lock-image=on/off" to "lock-mode=exclusive/shared/off". > Default is "lock-mode=exclusive" to exclusively lock RW images and shared > lock RO images; with lock-mode="shared", RW images are shared locked too; > lock-mode=off turns off image locking completely. > - Use F_OFD_SETLK fcntl so that close/dup on different fds are not a > problem. > - Update test cases. My comments after testing this patch set: * It's not possible to tell from the `qemu -help' output that this binary supports the lock-mode option. Please add this to the -help output (under `-drive') so we can detect it in qemu. * I patched libguestfs to add the `lock-image=off' flag when the drive is added readonly. This permits libguestfs to read live guests. I also checked that writing to live guests is now forbidden, and it is, which is good. In the write-to-live-guest case libguestfs will now fail with: qemu-system-x86_64: -drive file=/var/tmp/centos-6.img,cache=writeback,id=hd0,if=none: Failed to lock image So definitely we need this option to be reflected in the -help output. Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org