Re: [Qemu-devel] [PATCH v3 09/29] block: Introduce bdrv_aligned_preadv()

["Benoît Canet" <benoit.canet@irqsave.net>]

Le Friday 17 Jan 2014 à 15:14:59 (+0100), Kevin Wolf a écrit :
> This separates the part of bdrv_co_do_readv() that needs to happen
> before the request is modified to match the backend alignment, and a
> part that needs to be executed afterwards and passes the request to the
> BlockDriver.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
> Reviewed-by: Max Reitz <mreitz@redhat.com>
> ---
>  block.c | 61 +++++++++++++++++++++++++++++++++++++++++++------------------
>  1 file changed, 43 insertions(+), 18 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 25ae896..0c2baf5 100644
> --- a/block.c
> +++ b/block.c
> @@ -2705,26 +2705,24 @@ err:
>  }
>  
>  /*
> - * Handle a read request in coroutine context
> + * Forwards an already correctly aligned request to the BlockDriver. This
> + * handles copy on read and zeroing after EOF; any other features must be
> + * implemented by the caller.
>   */
> -static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
> -    int64_t sector_num, int nb_sectors, QEMUIOVector *qiov,
> -    BdrvRequestFlags flags)
> +static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
> +    int64_t offset, unsigned int bytes, QEMUIOVector *qiov, int flags)
unsigned int bytes <- Would it worth it to make this int64_t or size_t for the
not so far future where 4GB will be the new 4MB ?

Best regards

Benoît

>  {
>      BlockDriver *drv = bs->drv;
>      BdrvTrackedRequest req;
>      int ret;
>  
> -    if (!drv) {
> -        return -ENOMEDIUM;
> -    }
> -    if (bdrv_check_request(bs, sector_num, nb_sectors)) {
> -        return -EIO;
> -    }
> +    int64_t sector_num = offset >> BDRV_SECTOR_BITS;
> +    unsigned int nb_sectors = bytes >> BDRV_SECTOR_BITS;
>  
> -    if (bs->copy_on_read) {
> -        flags |= BDRV_REQ_COPY_ON_READ;
> -    }
> +    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> +    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
> +
> +    /* Handle Copy on Read and associated serialisation */
>      if (flags & BDRV_REQ_COPY_ON_READ) {
>          bs->copy_on_read_in_flight++;
>      }
> @@ -2733,11 +2731,6 @@ static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
>          wait_for_overlapping_requests(bs, sector_num, nb_sectors);
>      }
>  
> -    /* throttling disk I/O */
> -    if (bs->io_limits_enabled) {
> -        bdrv_io_limits_intercept(bs, nb_sectors, false);
> -    }
> -
>      tracked_request_begin(&req, bs, sector_num, nb_sectors, false);
>  
>      if (flags & BDRV_REQ_COPY_ON_READ) {
> @@ -2754,6 +2747,7 @@ static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
>          }
>      }
>  
> +    /* Forward the request to the BlockDriver */
>      if (!(bs->zero_beyond_eof && bs->growable)) {
>          ret = drv->bdrv_co_readv(bs, sector_num, nb_sectors, qiov);
>      } else {
> @@ -2794,6 +2788,37 @@ out:
>      return ret;
>  }
>  
> +/*
> + * Handle a read request in coroutine context
> + */
> +static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
> +    int64_t sector_num, int nb_sectors, QEMUIOVector *qiov,
> +    BdrvRequestFlags flags)
> +{
> +    BlockDriver *drv = bs->drv;
> +    int ret;
> +
> +    if (!drv) {
> +        return -ENOMEDIUM;
> +    }
> +    if (bdrv_check_request(bs, sector_num, nb_sectors)) {
> +        return -EIO;
> +    }
> +
> +    if (bs->copy_on_read) {
> +        flags |= BDRV_REQ_COPY_ON_READ;
> +    }
> +
> +    /* throttling disk I/O */
> +    if (bs->io_limits_enabled) {
> +        bdrv_io_limits_intercept(bs, nb_sectors, false);
> +    }
> +
> +    ret = bdrv_aligned_preadv(bs, sector_num << BDRV_SECTOR_BITS,
> +                             nb_sectors << BDRV_SECTOR_BITS, qiov, flags);
> +    return ret;
> +}
> +
>  int coroutine_fn bdrv_co_readv(BlockDriverState *bs, int64_t sector_num,
>      int nb_sectors, QEMUIOVector *qiov)
>  {
> -- 
> 1.8.1.4
> 
>