Re: [Qemu-devel] [PATCH] block: Use QEMU_IS_ALIGNED instead of reinventing it

[Nir Soffer <nsoffer@redhat.com>]

On Tue, Aug 20, 2019 at 10:51 PM Max Reitz <mreitz@redhat.com> wrote:

> On 17.08.19 19:53, Nir Soffer wrote:
> > Replace instances of:
> >
> >     (n & (BDRV_SECTOR_SIZE - 1)) == 0)
> >
> > With:
> >
> >     QEMU_IS_ALIGNED(n, BDRV_SECTOR_SIZE)
> >
> > Which reveals the intent of the code better, and makes it easier to
> > locate the code checking alignment.
> >
> > QEMU_IS_ALIGNED is implemented using %, which may be less efficient but
> > it is used only in assert() except one instance, so it should not
> > matter.
> >
> > Signed-off-by: Nir Soffer <nsoffer@redhat.com>
> > ---
> >  block/bochs.c | 4 ++--
> >  block/cloop.c | 4 ++--
> >  block/dmg.c   | 4 ++--
> >  block/io.c    | 8 ++++----
> >  block/qcow2.c | 4 ++--
> >  block/vvfat.c | 8 ++++----
> >  qemu-img.c    | 2 +-
> >  7 files changed, 17 insertions(+), 17 deletions(-)
>
> Because John was speaking about a magical incantation, I found
> BDRV_SECTOR_MASK.  There are two places in block/qcow2-cluster.c that
> use that to check alignment, I think those should be amended as well.
>

$ git grep BDRV_SECTOR_MASK
block/qcow2-cluster.c:        assert((offset_in_cluster &
~BDRV_SECTOR_MASK) == 0);
block/qcow2-cluster.c:        assert((bytes & ~BDRV_SECTOR_MASK) == 0);

Right, should use QEMU_IS_ALIGNED

include/block/block.h:#define BDRV_SECTOR_MASK   ~(BDRV_SECTOR_SIZE - 1)
include/block/block.h:#define BDRV_BLOCK_OFFSET_MASK  BDRV_SECTOR_MASK
migration/block.c:        flags = addr & ~BDRV_SECTOR_MASK;

This could use (BDRV_SECTOR_SIZE - 1).
In Linux SECTOR_MASK is defined as:

drivers/block/null_blk_main.c:#define SECTOR_MASK
(PAGE_SECTORS - 1)

It seems that qemu use use the same.

I will try to handle these in v2.

Nir