Re: [Xen-devel] bug when using 4K sectors?

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Mon, Aug 13, 2012 at 02:12:58PM +0000, James Harper wrote:
> I notice this code in drivers/block/xen-blkback/common.h
> 
> #define vbd_sz(_v)      ((_v)->bdev->bd_part ? \
>                          (_v)->bdev->bd_part->nr_sects : \
>                           get_capacity((_v)->bdev->bd_disk))
> 
> is the value returned by vbd_sz(_v) the number of sectors in the Linux device 
> (eg size / 4096), or the number of 512 byte sectors? I suspect the former 
> which is causing block requests beyond 1/8th the size of the device to fail 
> (assuming 4K sectors are expected to work at all - I can't quite get my head 
> around how it would be expected to work - does Linux do the read-modify-write 
> if required?)

I think you need to instrument it to be sure.. But more interesting, do you 
actually
have a disk that exposes a 4KB hardware and logical sector? So far I've only 
found
SSDs that expose a 512kB logical sector but also expose the 4KB hardware.

Never could figure out how that is all suppose to work as the blkback
is filled with << 9 on a bunch of things.

> 
> I can't test until tomorrow AEDT, but maybe someone here knows the answer 
> already?
> 
> James
> 
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