From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1IJEwX-0001rS-FS for qemu-devel@nongnu.org; Thu, 09 Aug 2007 16:49:17 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1IJEwU-0001oc-MQ for qemu-devel@nongnu.org; Thu, 09 Aug 2007 16:49:16 -0400 Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1IJEwU-0001oS-Eo for qemu-devel@nongnu.org; Thu, 09 Aug 2007 16:49:14 -0400 Received: from an-out-0708.google.com ([209.85.132.244]) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1IJEwU-0000w5-3x for qemu-devel@nongnu.org; Thu, 09 Aug 2007 16:49:14 -0400 Received: by an-out-0708.google.com with SMTP id d11so166151and for ; Thu, 09 Aug 2007 13:49:13 -0700 (PDT) Message-ID: <46BB7DC6.3060400@codemonkey.ws> Date: Thu, 09 Aug 2007 15:49:10 -0500 From: Anthony Liguori MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH 4/4][RFC] Add logic to QEMU to read command line options from qcow2 images References: <59abf66e0708081124g14901b01i841b70d17ae1e097@mail.gmail.com> <59abf66e0708081252of2948d7we85c9084bad245d4@mail.gmail.com> <20070808202428.GA25050@redhat.com> <46BB2A99.3030609@codemonkey.ws> <46BB7625.2050900@qumranet.com> <46BB7842.1030101@codemonkey.ws> <46BB7966.3090007@qumranet.com> <46BB79ED.2020503@codemonkey.ws> <1186692263.20963.42.camel@wombat.dlib.indiana.edu> In-Reply-To: <1186692263.20963.42.camel@wombat.dlib.indiana.edu> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Brian Wheeler wrote: > On Thu, 2007-08-09 at 15:32 -0500, Anthony Liguori wrote: > >> Avi Kivity wrote: >> >>> Anthony Liguori wrote: >>> >>>> If you're looking for a low-end solution, another possibility would >>>> be having a "new" file format which consisted of: >>>> >>>> #!/path/to/qemu [ ...] >>>> >>>> >>>> And then make the appropriate changes to QEMU such that it can skip >>>> the first line in a disk image file. This has a few nice side >>>> effects. The disk image is directly executable and it makes it very >>>> clear to the user that they have to trust the disk image. The other >>>> nice thing is that it would work with file formats other than qcow2. >>>> >>> Well, it would be nice to align the disk image to a sector boundary >>> (or, better, a page boundary). But yes, a very good idea. >>> >> That has the very nice side effect of allowing you to edit the command >> line with a text editor provided you don't cross the sector boundary. >> Filling with spaces would be pretty nice. >> >> > > > Its a bad idea. Either have a line terminated file, or a pure binary > file, but don't mix them. Besides firing up an editor to modify it > being a royal pain, mystery breakages will occur when someone has their > editor set to "insert mode" (which is the default) vs "overwrite mode" > and doesn't notice those extra spaces moving beyond the 512-byte mark. > > Brian > Assuming that you have a tool that edits the command line (I admit, using emacs is a bad idea), then aligning to a sector boundary means that you don't have to munge the data every time you update. Since most command lines will be < 512 bytes probably, this means that you can usually get away with not having to copy any data on disk which is a very good thing when you have multi-gigabyte files. Regards, Anthony Liguori >> Regards, >> >> Anthony Liguori >> >> >> >> > > > > >