Re: [Qemu-devel] [PATCH 2/6] block: Prepare bdrv_aligned_preadv() for byte-aligned requests

[Eric Blake <eblake@redhat.com>]

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On 06/08/2016 08:10 AM, Kevin Wolf wrote:
> This patch makes bdrv_aligned_preadv() ready to accept byte-aligned
> requests. Note that this doesn't mean that such requests are actually
> made. The caller still ensures that all requests are aligned to at least
> 512 bytes.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block/io.c | 41 +++++++++++++++++------------------------
>  1 file changed, 17 insertions(+), 24 deletions(-)
> 
> diff --git a/block/io.c b/block/io.c
> index 3b34f20..2fd88cb 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -959,11 +959,6 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
>  {
>      int ret;
>  
> -    int64_t sector_num = offset >> BDRV_SECTOR_BITS;
> -    unsigned int nb_sectors = bytes >> BDRV_SECTOR_BITS;
> -
> -    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> -    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);

My recent patch proposal conflicts here; I can drop (or rebase) mine,
but I think you want to keep the asserts, after modifying them to:

assert((offset & (align - 1)) == 0);
assert((bytes & (align - 1)) == 0);

and maybe add 'assert(is_power_of_2(align)); for good measure.


>  
> -        max_nb_sectors = ROUND_UP(MAX(0, total_sectors - sector_num),
> -                                  align >> BDRV_SECTOR_BITS);
> -        if (nb_sectors < max_nb_sectors) {
> +        max_bytes = ROUND_UP(MAX(0, total_bytes - offset), align);
> +        if (bytes < max_bytes) {

Another one of my posted patches switches this to <= to avoid a harmless
off-by-one, also something I can rebase.

Whether you add the assertions, or leave it for me to (re-)add them in
my rebase,

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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