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

Laszlo Ersek lersek at redhat.com
Tue Apr 5 18:49:43 CEST 2016

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).


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