Re: [SeaBIOS] virtio-blk ... block size 4096 is unsupported

[James Shimer]

Thanks for the responses.  What you've both said makes total sense.  We've tried 512 logical/ 4k physical and it works fine with Seabios.  Thanks Laszlo for the OVMF tip, that's totally the route we need to take.

________________________________________
From: Laszlo Ersek 
Sent: Tuesday, April 5, 2016 12:49 PM
To: Kevin O'Connor
Cc: James Shimer; Kevin Wolf; [e-mail]
Subject: Re: [SeaBIOS] virtio-blk ... block size 4096 is unsupported

On 04/05/16 18:36, Kevin O'Connor wrote:
> On Tue, Apr 05, 2016 at 02:31:53PM +0200, Laszlo Ersek wrote:
> > On 04/05/16 06:25, James Shimer wrote:
> > > I've been doing some testing if KVM with 4K physical sector virtio
> > > disks and they work with KVM as a none boot disk.  We'd like to be
> > > able to boot a 4k physical sector disk in KVM, is there 4K support in
> > > any seabios newer/upcoming releases, or is there a way to configure
> > > for 4k sectors?
> > >
> > > reference from master
> > > src/hw/virtio-blk.c lin 142
> > >    if (vdrive->drive.blksize != DISK_SECTOR_SIZE) {
> > >         dprintf(1, "virtio-blk %pP block size %d is unsupported\n",
> > >                 pci, vdrive->drive.blksize);
> > >         goto fail;
> > >     }
> >
> > This code dates back to 4030db0d2c5a7.
> >
> > I'm not an expert, but I think BIOS interfaces don't support a sector
> > size different from 512 B. It seems that a drive with 4096 B physical
> > sectors should enable (the emulation of) a 512 B logical sector size, so
> > that it can work with code that assumes an 512 B sector size.
> >
> > https://en.wikipedia.org/wiki/Advanced_Format#512e
>
> The EDD standard ( https://en.wikipedia.org/wiki/Enhanced_Disk_Drive )
> allows for 4K blocks.  However, the older BIOS interface (eg, int
> 1301) only support 512 byte sectors.  This means that the BIOS would
> need to emulate 512 byte reads should one of the older interfaces be
> called on one of these drives.  This isn't difficult as SeaBIOS
> already does this for cdroms.

That sounds great, thanks. I should have thought of CD-ROMs, I guess.
> > I guess for a virtio-blk disk, that means:
> >
> > -device virtio-blk-pci,physical_block_size=4096,logical_block_size=512
>
> In practice, almost all real drives seem to do the above.  So, adding
> support for drives that don't has not previously been a priority.

Right, I missed that 512e could be implemented in SeaBIOS itself (and I
completely missed that it had been, for CD-ROMs).

Thanks!
Laszlo