Re: [Qemu-devel] [RFC PATCH 0/3] block: add support for 4k logical blocks

[Paolo Bonzini]

On 11/25/2011 08:26 AM, Mark Wu wrote:
> 1. This patch aims to add 4k logical support for qemu running on a host
> with 4k logical block size, right?

No, it adds support for 512b logical block sizes running on a host with 
4k logical block size and cache=none.  This is suboptimal as it requires 
bounce buffers, but it can happen with migration and until libvirt 
provides a knob for the guest's logical block size.

> For guest, we can use
> logical_block_size=4096 to achieve that even on a host with the
> logical_block_size of 512. Am I right?

Yes.

> 2. Can we just call bdrv_get_alignment in bdrv_open_common once and use
> the stored buffer_alignment for future usage instead of always
> calling bdrv_get_alignment in qemu_blockalign/qiov_is_aligned.  What's
> the benefit of the dynamic way?

Yes, I think it's possible.

Paolo