Re: [Qemu-devel] [PATCH 2/6] change vectored block I/O API to plain iovecs

[Anthony Liguori]

Avi Kivity wrote:
> Christoph Hellwig wrote:
> > QEMUIOVector is a useful helper for the dma-helper.c internals but 
> > for a generic
> > block API it's more of hindrance.  Some top-level consumers like 
> > virtio-blk
> > already have the plain iovec and segment number at hand and can pass 
> > it down
> > directly, and for those that just have a single element and need to 
> > fake up
> > a vector the plain iovec also is a lot easier.
> >   
>
> virtio gets its iovecs through a hacky (and incorrect, try >=4G) 
> method.  IMO virtio should be fixed to use the dma api, at which point 
> it will start to use QEMUIOVector anyway,

>= 4GB should work fine in virtio.  It basically replicates the DMA API 
today.  It doesn't handle MMIO memory though.

> > Last but not leas we want to push down vectored I/O to the lowest level,
> > and if posix-aio-compat.c wants to stay somewhat true to it's goal of
> > beeing like an ehanced posix AIO API it should stick to posix types.
> >   
>
> Internally yes, but why should bdrv_* not use QEMUIOVector?  That API 
> isn't very interested in posix.

Agreed.

Regards,

Anthony Liguori