Re: [Qemu-devel] [PATCH 00/17] block: Convert .bdrv_read/write to .bdrv_preadv/pwritev

[Stefan Hajnoczi]

On Wed, Apr 27, 2016 at 11:52:30AM +0200, Kevin Wolf wrote:
> This series introduces a new BlockDriver interface, which will hopefully be 
> the
> final one, or at least good enough for another few years: 
> .bdrv_preadv/pwritev.
> It is based on coroutines, vectored, has flags and uses a byte granularity.
> This is now the preferred interface for new drivers.
> 
> All drivers still using the legacy interface .bdrv_read/write are converted to
> the new interface and the emulation code we had for the old interface is
> removed. Most of the drivers become zero-copy with these patches as they are
> vectored now; only vvfat continues to allocate a bounce buffer.
> 
> The less obscure formats (vmdk, vdi, vpc) also natively support byte-aligned
> requests now. The block layer is still enforcing a minimal alignment of 512, 
> so
> this isn't actually used yet, but in a next step, we can lift this restriction
> for drivers that implement .bdrv_preadv/pwritev.
> 
> Kevin Wolf (17):
>   block: Introduce bdrv_driver_preadv()
>   block: Introduce bdrv_driver_pwritev()
>   block: Support AIO drivers in bdrv_driver_preadv/pwritev()
>   block: Rename bdrv_co_do_preadv/writev to bdrv_co_preadv/writev
>   block: Introduce .bdrv_co_preadv/pwritev BlockDriver function
>   bochs: Implement .bdrv_co_preadv() interface
>   cloop: Implement .bdrv_co_preadv() interface
>   dmg: Implement .bdrv_co_preadv() interface
>   vdi: Implement .bdrv_co_preadv() interface
>   vdi: Implement .bdrv_co_pwritev() interface
>   vmdk: Add vmdk_find_offset_in_cluster()
>   vmdk: Implement .bdrv_co_preadv() interface
>   vmdk: Implement .bdrv_co_pwritev() interface
>   vpc: Implement .bdrv_co_preadv() interface
>   vpc: Implement .bdrv_co_pwritev() interface
>   vvfat: Implement .bdrv_co_preadv/pwritev interfaces
>   block: Remove BlockDriver.bdrv_read/write
> 
>  block.c                   |   2 -
>  block/block-backend.c     |   4 +-
>  block/bochs.c             |  46 ++++---
>  block/cloop.c             |  33 ++---
>  block/dmg.c               |  36 +++---
>  block/io.c                | 317 +++++++++++++++++++--------------------------
>  block/iscsi.c             |   8 --
>  block/nbd.c               |   9 --
>  block/raw_bsd.c           |  12 +-
>  block/vdi.c               | 127 ++++++++++--------
>  block/vmdk.c              | 320 
> ++++++++++++++++++++++++++++------------------
>  block/vpc.c               | 165 ++++++++++++------------
>  block/vvfat.c             |  55 ++++++--
>  hw/ide/macio.c            |   4 +-
>  include/block/block_int.h |  12 +-
>  15 files changed, 609 insertions(+), 541 deletions(-)

The idea to support byte-granularity requests is interesting.  Seems
like there is not much stopping that anymore.

Please check all block driver changes to make sure the CoMutex is
unlocked in error return code paths.  I only pointed it out the first
few times but there are more instances later in the series with missing
unlocks.

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