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Date: Thu, 18 Jul 2013 09:43:27 +0800
From: Stefan Hajnoczi <stefanha@gmail.com>
Message-ID: <20130718014327.GA21598@stefanha-thinkpad.redhat.com>
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Subject: Re: [Qemu-devel] [Bug 1186303] [NEW] virtual fat do not working in
 qemu 1.5.0
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To: Bug 1186303 <1186303@bugs.launchpad.net>
Cc: qemu-devel@nongnu.org

On Fri, May 31, 2013 at 03:26:47PM -0000, prochazka nicolas wrote:
> Public bug reported:
> 
> Guest : windows Seven / XP
> Qemu version : 1.5.0 
> cmd line : 
> -drive file=fat:floppy:/mnt/vdisk/diskconf/TEST004/,if=none,id=drive-fdc0-0-0,readonly=on 
> generated by  libvirt :
>  
> <disk type='dir' device='floppy'>
>       <driver name='qemu' type='fat'/>
>       <source dir='/mnt/vdisk/diskconf/TEST003/'/>
>       <target dev='fda' bus='fdc'/>
>       <readonly/>
>       <alias name='fdc0-0-0'/>
>       <address type='drive' controller='0' bus='0' target='0' unit='0'/>
>     </disk>
> 
> works with qemu <= 1.4.1
> 
> with qemu 1.5.0 , guest does not see the floppy content.

Thanks for reporting this bug.  The vvfat block driver is not actively
maintained, but you can help us track down this bug:

Since it used to work in QEMU 1.4.1 you could use git-bisect(1) to
identify the commit that broke vvfat.

http://git-scm.com/book/en/Git-Tools-Debugging-with-Git#Binary-Search
https://www.kernel.org/pub/software/scm/git/docs/git-bisect.html
http://code-worrier.com/blog/git-bisect-basics/

Something along the lines of:

$ git clone git://git.qemu.org/qemu.git
$ cd qemu
$ git bisect start
$ git bisect bad master
$ git bisect good v1.4.1

Then build from source and test at each bisect step:

$ ./configure --target-list=x86_64-softmmu && make
$ qemu -drive file=fat:floppy:...

If it fails:

$ git bisect bad

If it succeeds:

$ git bisect good

At the end of the process it will tell you which commit broke vvfat.

Stefan