Re: [Qemu-devel] [Qemu-block] [PATCH] block.c: fix real cdrom detection

[Stefan Hajnoczi]

On Thu, Jun 25, 2015 at 11:11:24AM -0400, Programmingkid wrote:
> On Jun 25, 2015, at 9:31 AM, Stefan Hajnoczi wrote:
> > On Tue, Jun 23, 2015 at 02:26:51PM -0400, Programmingkid wrote:
> >> On Jun 23, 2015, at 2:06 PM, John Snow wrote:
> >>> So what's the issue that this patch attempts to fix and how did you
> >>> determine that the fix was needed here? It doesn't look like it respects
> >>> proper abstraction at a glance.
> >> 
> >> Without the patch, QEMU would just quit when the "-cdrom /dev/cdrom" 
> >> option is given.
> > 
> > Why does it quit?
> 
> Because of a bug. This is what it prints: "Could not read image for 
> determining its format: Invalid argument".

The bdrv_pread() failure is what need you need to investigate.  In the
other sub-thread there have been hints about adding CD-ROM passthrough
support on Mac OS X by filling in the missing parts in
block/raw-posix.c.  That should help you get to the bottom of the
problem.

> This message seems to indicate that QEMU thinks the real cdrom drive is an 
> image file. 

If the -drive format= option is not given, QEMU will try to detect the
image format.  That's the purpose of the find_image_format() function.

QEMU does not make a distinction between image files and block devices
because there are valid use cases where a block device uses an image
format.  For example, a disk or partition can contain qcow2 data (there
is no partition table or file system, just qcow2).

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