From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49342) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZCmtb-0003lQ-HT for qemu-devel@nongnu.org; Wed, 08 Jul 2015 06:48:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZCmta-0001Rj-IU for qemu-devel@nongnu.org; Wed, 08 Jul 2015 06:48:07 -0400 Message-ID: <559CFFDD.3000704@redhat.com> Date: Wed, 08 Jul 2015 12:47:57 +0200 From: Laurent Vivier MIME-Version: 1.0 References: <55952D97.7040009@redhat.com> <559540F6.9090800@redhat.com> <55954384.9010906@redhat.com> <559544C4.4050809@redhat.com> <55954836.3060700@redhat.com> <20150708103125.GE4117@noname.redhat.com> In-Reply-To: <20150708103125.GE4117@noname.redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] raw-posix.c: remove raw device access for cdrom List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf Cc: Peter Maydell , Qemu-block , Stefan Hajnoczi , qemu-devel qemu-devel , Programmingkid , Paolo Bonzini , John Snow On 08/07/2015 12:31, Kevin Wolf wrote: > Am 02.07.2015 um 16:18 hat Laurent Vivier geschrieben: >> >> >> On 02/07/2015 16:03, Paolo Bonzini wrote: >>> >>> >>> On 02/07/2015 15:58, Laurent Vivier wrote: >>>> Since any /dev entry can be treated as a raw disk image, it is worth >>>> noting which devices can be accessed when and how. /dev/rdisk nodes are >>>> character-special devices, but are "raw" in the BSD sense and force >>>> block-aligned I/O. They are closer to the physical disk than the buffer >>>> cache. /dev/disk nodes, on the other hand, are buffered block-special >>>> devices and are used primarily by the kernel's filesystem code. >>> >>> So the right thing to do would not be just to set need_alignment, but to >>> probe it like we do on Linux for BDRV_O_NO_CACHE. >>> >>> I'm okay with doing the simple thing, but it needs a comment for non-BSDers. >> >> So, what we have to do, in our case, for MacOS X cdrom, is something like: >> >> ... GetBSDPath ... >> ... >> if (flags & BDRV_O_NOCACHE) { >> strcat(bsdPath, "r"); >> } >> ... > > I would avoid such magic. What we could do is rejecting /dev/rdisk nodes > without BDRV_O_NOCACHE. It's not how it works... Look in hdev_open(). If user provides /dev/cdrom on the command line, in the case of MacOS X, QEMU searches for a cdrom drive in the system and set filename to /dev/rdiskX according to the result. Perhaps this part should be removed. But if we just want to correct the bug, we must not set filename to /dev/rdiskX if NOCACHE is not set but to /dev/diskX It's the aim of this change. Laurent