[Qemu-discuss] Host drive basics.

[peter]

An explanation for anyone interested.

From:   Peter Easthope
Date:   Mon, 17 Nov 2014 18:02:09 -0800
> Therefore take any diskette which the bare PC can boot from and
> try to boot the virtual machine from it.
> 
> Here fd0 twitches; then an error.
> address@hidden:~$ sudo qemu-system-i386 -fda /dev/fd0 -vga std -boot a
> qemu-system-i386: -fda /dev/fd0: could not open disk image /dev/fd0:
> Input/output error
> 
> I/O error?  Why?  Certainly it is read/writable.
> 
> address@hidden:~$ ls -l /dev/fd0
> brw-rw---T 1 root floppy 2, 0 Nov 17 16:44 /dev/fd0

Read/writable according to filesystem permission but the write protection 
tab was open.  "-fda /dev/fd0" attempts to mount or mounts the device in 
the virtual machine rw and yields the error.  The solution is to invoke the 
diskette readonly.  

http://www.ocp.inf.ethz.ch/wiki/Documentation/Installation#toc23
For a real diskette, write-protected.
sudo qemu-system-i386 -drive file=/dev/fd0,index0,if=floppy,readonly -drive 
file=/dev/sda,media=disk -vga std -boot a

Given that a real machine boots from a write-protected diskette with no 
complaint, I'm not sure of the logic in this case; but that's how it is.

Regards,                         ... Peter E.

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