Re: [Qemu-devel] [PATCH v2 02/10] block: New bdrv_nb_sectors()

[Eric Blake]

On 05/28/2014 08:25 AM, Markus Armbruster wrote:
> A call to retrieve the image size converts between bytes and sectors
> several times:
> 
> * BlockDriver method bdrv_getlength() returns bytes.
> 
> * refresh_total_sectors() converts to sectors, rounding up, and stores
>   in total_sectors.
> 
> * bdrv_getlength() converts total_sectors back to bytes (now rounded
>   up to a multiple of the sector size).
> 
> * Callers wanting sectors rather bytes convert it right back.
>   Example: bdrv_get_geometry().
> 
> bdrv_nb_sectors() provides a way to omit the last two conversions.
> It's exactly bdrv_getlength() with the conversion to bytes omitted.
> It's functionally like bdrv_get_geometry() without its odd error
> handling.
> 
> Reimplement bdrv_getlength() and bdrv_get_geometry() on top of
> bdrv_nb_sectors().
> 
> The next patches will convert some users of bdrv_getlength() to
> bdrv_nb_sectors().
> 
> Signed-off-by: Markus Armbruster <address@hidden>
> ---
>  block.c               | 29 +++++++++++++++++++----------
>  include/block/block.h |  1 +
>  2 files changed, 20 insertions(+), 10 deletions(-)

Reviewed-by: Eric Blake <address@hidden>

> +/**
> + * Return length in bytes on success, -errno on error.
> + * The length is always a multiple of BDRV_SECTOR_SIZE.
> + */
> +int64_t bdrv_getlength(BlockDriverState *bs)

The second sentence might not always be true in the future if we add
support for image length not a multiple of sector size; but we can
correct it at the point we make such a change.  For now, it is worth
keeping.

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

signature.asc
Description: OpenPGP digital signature