Re: [Qemu-devel] [PATCH] fdc: fix MAX_FD probelm

[Stuart Brady <sdbrady@ntlworld.com>]

On Mon, Sep 14, 2009 at 12:42:32AM +0900, TAKEDA, toshiya wrote:
> Dear Stuart and members,
> 
> >I'm still slightly concerned that for machines with MAX_PHYSICAL_DRIVES
> >set to 2, guests would see drives 2 and 3 as present, but with no disk
> >inserted.  Previously, though, I expect they would have been mirrors of
> >drives 0 and 1, which is obviously worse!
> 
> FD_DOR_SELMASK is not affected by MAX_PHYSICAL_DRIVES and is fixed to 3,
> so I think drive 2 and 3 are not recognized as the mirror of 0 and 1.

Agreed.

(Just to clarify, my comment about mirrors of drives 2 and 3 was
referring to the old code, when FD_DOR_SELMASK was affected by MAX_FD.)

> Well, I also think it is better the user can select the physical drive
> number, not only 2 but 0, 1 and 3.
> But it will require the large scale patch, for example the block and
> qemu option commands.

The user should really be able to attach drives individually, and have
only drive 3 connected, if they want... but that's a separate problem.

> If this patch is acceptable for commit, I will reimplement PC-09 patch
> based on it and in this time I hope I can fix the sence interrupt status.

My only concern is that a guest OS might now reserve drive letters for
drives 2 and 3, whereas before, it might have ignored those drives
because it was not possible to select them.

In reality, it seems a greater concern that without this patch, a
guest OS might allow access to the mirrors of drives 0 and 1,
potentially causing filesystem corruption. :-(

Cheers,
-- 
Stuart Brady