Re: [Qemu-devel] [RFC PATCH 06/17] block: use bdrv_{co, aio}_discard for write_zeroes operations

[Christoph Hellwig]

On Wed, Mar 14, 2012 at 01:14:18PM +0100, Paolo Bonzini wrote:
> 
> Note that the discard granularity is only a hint, so it's really more a
> maximum suggested value than a granularity.  Outside of a cluster
> boundary the format would still have to write zeros manually.
> 
> Also, Linux for example will only round the number of sectors down to
> the granularity, not the start sector.

Which really is more of a bug than a feature.  The current discard
implementation in Linux is still very poor.