From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:53636) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZCn6w-0003XK-UZ for qemu-devel@nongnu.org; Wed, 08 Jul 2015 07:01:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZCn6t-0001bg-0u for qemu-devel@nongnu.org; Wed, 08 Jul 2015 07:01:54 -0400 Date: Wed, 8 Jul 2015 13:01:40 +0200 From: Kevin Wolf Message-ID: <20150708110140.GF4117@noname.redhat.com> 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> <559CFFDD.3000704@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <559CFFDD.3000704@redhat.com> 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: Laurent Vivier Cc: Peter Maydell , Qemu-block , Stefan Hajnoczi , qemu-devel qemu-devel , Programmingkid , Paolo Bonzini , John Snow Am 08.07.2015 um 12:47 hat Laurent Vivier geschrieben: > > > 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. Oh, we're already playing such games... I guess you're right then. It even seems to be not only for '/dev/cdrom', but for everything starting with this string. Does anyone know what's the reason for that? Also, I guess before doing strcat() on bsdPath, we should check the buffer length... > 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. Yes, that looks right. Kevin