Re: [Qemu-devel] [PATCH v3 18/20] block: Make bdrv_is_allocated() byte-based

[Juan Quintela <quintela@redhat.com>]

Eric Blake <eblake@redhat.com> wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  In the common case, allocation is unlikely to ever use
> values that are not naturally sector-aligned, but it is possible
> that byte-based values will let us be more precise about allocation
> at the end of an unaligned file that can do byte-based access.
>
> Changing the signature of the function to use int64_t *pnum ensures
> that the compiler enforces that all callers are updated.  For now,
> the io.c layer still assert()s that all callers are sector-aligned
> on input and that *pnum is sector-aligned on return to the caller,
> but that can be relaxed when a later patch implements byte-based
> block status.  Therefore, this code adds usages like
> DIV_ROUND_UP(,BDRV_SECTOR_SIZE) to callers that still want aligned
> values, where the call might reasonbly give non-aligned results
> in the future; on the other hand, no rounding is needed for callers
> that should just continue to work with byte alignment.
>
> For the most part this patch is just the addition of scaling at the
> callers followed by inverse scaling at bdrv_is_allocated().  But
> some code, particularly bdrv_commit(), gets a lot simpler because it
> no longer has to mess with sectors; also, it is now possible to pass
> NULL if the caller does not care how much of the image is allocated
> beyond the initial offset.
>
> For ease of review, bdrv_is_allocated_above() will be tackled
> separately.
>
> Signed-off-by: Eric Blake <eblake@redhat.com>
> Reviewed-by: John Snow <jsnow@redhat.com>

Reviewed-by: Juan Quintela <quintela@redhat.com>