Re: [Qemu-devel] [PATCH] raw: Use the right host device driver for open/create
So the proposed patch is too hacky, but nobody likes to discuss what the right way is? What about 0.12? Are we just going to provide the current bad user interface? Kevin
Re: [Qemu-devel] [PATCH] raw: Use the right host device driver for open/create
Am 30.11.2009 21:51, schrieb Christoph Hellwig: On Mon, Nov 30, 2009 at 04:54:31PM +0100, Kevin Wolf wrote: Users don't expect that they need to specify host_device/cdrom/floppy when creating an image on a block device or converting with an device as target. Currently creating as raw leads to 'Error while formatting' whereas using as raw just works. With this patch raw is accepted for both files and host devices. For devices the block driver is transparently changed to host_*. I agree that we should allow raw to also cover host devices, but I don't like the implementation very much. Beeing used to specify the format is pretty much the only reason to have the name in the block driver anyway, and looking it up in one is a bit of a layering violation. Ok, if you start talking about layering, we can have a fundamental discussion on this topic and why the layering is broken anyway. Logically, we have image formats like qcow2, VMDK and raw, and they are stored in files, on CD-ROMs or general block devices. From a layering perspective, it is wrong to include the latter in the raw format driver in the first place. I'd suggest to either allow multiple formats with the same name and looping over them or some sort of alias property in the block driver to also match the alias instead. I don't like taking the same name for multiple formats very much. You get a bug report with a raw image and need to start guessing which of the many raws could be meant. Adding some kind of a parent driver field to the driver definition and probing for which of the children is used could work though (it would basically mean moving the code of this patch into block.c). I'm not sure if such an abstraction is needed when there is only one user anyway (same argument as yours with AIO, even though there are two users), but I'm not opposed to it. It just won't help much in getting the layering right. In the end, I don't care too much which way it is implemented, but I do want to present the right user interface in 0.12. Kevin
Re: [Qemu-devel] [PATCH] raw: Use the right host device driver for open/create
Christoph Hellwig wrote: On Mon, Nov 30, 2009 at 04:54:31PM +0100, Kevin Wolf wrote: Users don't expect that they need to specify host_device/cdrom/floppy when creating an image on a block device or converting with an device as target. Currently creating as raw leads to 'Error while formatting' whereas using as raw just works. With this patch raw is accepted for both files and host devices. For devices the block driver is transparently changed to host_*. I agree that we should allow raw to also cover host devices, but I don't like the implementation very much. Beeing used to specify the format is pretty much the only reason to have the name in the block driver anyway, and looking it up in one is a bit of a layering violation. I agree. I'd suggest to either allow multiple formats with the same name and looping over them or some sort of alias property in the block driver to also match the alias instead. Regards, Anthony Liguori
Re: [Qemu-devel] [PATCH] raw: Use the right host device driver for open/create
On Mon, Nov 30, 2009 at 04:54:31PM +0100, Kevin Wolf wrote: Users don't expect that they need to specify host_device/cdrom/floppy when creating an image on a block device or converting with an device as target. Currently creating as raw leads to 'Error while formatting' whereas using as raw just works. With this patch raw is accepted for both files and host devices. For devices the block driver is transparently changed to host_*. I agree that we should allow raw to also cover host devices, but I don't like the implementation very much. Beeing used to specify the format is pretty much the only reason to have the name in the block driver anyway, and looking it up in one is a bit of a layering violation. I'd suggest to either allow multiple formats with the same name and looping over them or some sort of alias property in the block driver to also match the alias instead.
