Re: [Qemu-devel] [RFC PATCH 00/19] block: Support for 512b-on-4k emulation

[Paolo Bonzini]

Il 06/12/2013 18:22, Kevin Wolf ha scritto:
> This patch series adds code to the block layer that allows performing
> I/O requests in smaller granularities than required by the host backend
> (most importantly, O_DIRECT restrictions). It achieves this for reads
> by rounding the request to host-side block boundary, and for writes by
> performing a read-modify-write cycle (and serialising requests
> touching the same block so that the RMW doesn't write back stale data).
> 
> Originally I intended to reuse a lot of code from Paolo's previous
> patch series, however as I tried to integrate pread/pwrite, which
> already do a very similar thing (except for considering concurrency),
> and because I wanted to implement zero-copy, most of this series ended
> up being new code.

Very nice!  There's not much to comment on regarding the 512-on-4k part.

Just one question.  Do you think we could make our emulated disks
512b-logical/4k-physical (512E) by default?  In other words, I don't
remember the outcome of our discussion on whether the standard promises
a 4k write granularity for this configuration.

Paolo