Re: [Qemu-devel] [PATCH 2/5] block: New bdrv_nb_sectors()

[Kevin Wolf <kwolf@redhat.com>]

Am 09.05.2014 um 11:48 hat Markus Armbruster geschrieben:
> 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 <armbru@redhat.com>

Is this really the right direction to move?

Generally I think we should be trying to move away from those arbitrary
units of 512 bytes (that are called sectors for some reason, but aren't
really related to either guest or host sector sizes), and towards
interfaces that use byte granularity.

So I would rather see bs->total_sectors becoming bs->total_bytes than
adding a new sector-based function.

Kevin