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

[Nir Soffer]

On Tue, Aug 20, 2019 at 10:30 PM John Snow <address@hidden> wrote:

>
>
> On 8/17/19 1:53 PM, Nir Soffer wrote:
> > Replace instances of:
> >
> >     (n & (BDRV_SECTOR_SIZE - 1)) == 0)
> >
> > With:
> >
> >     QEMU_IS_ALIGNED(n, BDRV_SECTOR_SIZE)
> >
>
> Do you have a magical incantation you used to find these?
>

I found the first by accident, then I used:

    git grep 'BDRV_SECTOR_SIZE - 1'

> 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.
> >
>
> There is virtually no way these aren't optimized by the compiler.
>

Makes sense, but I did not check.


>
> > Signed-off-by: Nir Soffer <address@hidden>
>
> Therefore:
>
> Reviewed-by: John Snow <address@hidden>
>
> > ---
> >  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(-)
> >
> > diff --git a/block/bochs.c b/block/bochs.c
> > index 962f18592d..32bb83b268 100644
> > --- a/block/bochs.c
> > +++ b/block/bochs.c
> > @@ -248,8 +248,8 @@ bochs_co_preadv(BlockDriverState *bs, uint64_t
> offset, uint64_t bytes,
> >      QEMUIOVector local_qiov;
> >      int ret;
> >
> > -    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> > -    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
> > +    assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
> > +    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
> >
> >      qemu_iovec_init(&local_qiov, qiov->niov);
> >      qemu_co_mutex_lock(&s->lock);
> > diff --git a/block/cloop.c b/block/cloop.c
> > index 384c9735bb..4de94876d4 100644
> > --- a/block/cloop.c
> > +++ b/block/cloop.c
> > @@ -253,8 +253,8 @@ cloop_co_preadv(BlockDriverState *bs, uint64_t
> offset, uint64_t bytes,
> >      int nb_sectors = bytes >> BDRV_SECTOR_BITS;
> >      int ret, i;
> >
> > -    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> > -    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
> > +    assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
> > +    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
> >
> >      qemu_co_mutex_lock(&s->lock);
> >
> > diff --git a/block/dmg.c b/block/dmg.c
> > index 45f6b28f17..4a045f2b3e 100644
> > --- a/block/dmg.c
> > +++ b/block/dmg.c
> > @@ -697,8 +697,8 @@ dmg_co_preadv(BlockDriverState *bs, uint64_t offset,
> uint64_t bytes,
> >      int nb_sectors = bytes >> BDRV_SECTOR_BITS;
> >      int ret, i;
> >
> > -    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> > -    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
> > +    assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
> > +    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
> >
> >      qemu_co_mutex_lock(&s->lock);
> >
> > diff --git a/block/io.c b/block/io.c
> > index 56bbf195bb..7508703ecd 100644
> > --- a/block/io.c
> > +++ b/block/io.c
> > @@ -1080,8 +1080,8 @@ static int coroutine_fn
> bdrv_driver_preadv(BlockDriverState *bs,
> >      sector_num = offset >> BDRV_SECTOR_BITS;
> >      nb_sectors = bytes >> BDRV_SECTOR_BITS;
> >
> > -    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> > -    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
> > +    assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
> > +    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
> >      assert(bytes <= BDRV_REQUEST_MAX_BYTES);
> >      assert(drv->bdrv_co_readv);
> >
> > @@ -1133,8 +1133,8 @@ static int coroutine_fn
> bdrv_driver_pwritev(BlockDriverState *bs,
> >      sector_num = offset >> BDRV_SECTOR_BITS;
> >      nb_sectors = bytes >> BDRV_SECTOR_BITS;
> >
> > -    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> > -    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
> > +    assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
> > +    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
> >      assert(bytes <= BDRV_REQUEST_MAX_BYTES);
> >
> >      assert(drv->bdrv_co_writev);
> > diff --git a/block/qcow2.c b/block/qcow2.c
> > index 59cff1d4cb..41cab70e1d 100644
> > --- a/block/qcow2.c
> > +++ b/block/qcow2.c
> > @@ -2072,8 +2072,8 @@ static coroutine_fn int
> qcow2_co_preadv(BlockDriverState *bs, uint64_t offset,
> >              }
> >              if (bs->encrypted) {
> >                  assert(s->crypto);
> > -                assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> > -                assert((cur_bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
> > +                assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
> > +                assert(QEMU_IS_ALIGNED(cur_bytes, BDRV_SECTOR_SIZE));
> >                  if (qcow2_co_decrypt(bs, cluster_offset, offset,
> >                                       cluster_data, cur_bytes) < 0) {
> >                      ret = -EIO;
> > diff --git a/block/vvfat.c b/block/vvfat.c
> > index f6c28805dd..019b8f1341 100644
> > --- a/block/vvfat.c
> > +++ b/block/vvfat.c
> > @@ -1547,8 +1547,8 @@ vvfat_co_preadv(BlockDriverState *bs, uint64_t
> offset, uint64_t bytes,
> >      int nb_sectors = bytes >> BDRV_SECTOR_BITS;
> >      void *buf;
> >
> > -    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> > -    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
> > +    assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
> > +    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
> >
> >      buf = g_try_malloc(bytes);
> >      if (bytes && buf == NULL) {
> > @@ -3082,8 +3082,8 @@ vvfat_co_pwritev(BlockDriverState *bs, uint64_t
> offset, uint64_t bytes,
> >      int nb_sectors = bytes >> BDRV_SECTOR_BITS;
> >      void *buf;
> >
> > -    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
> > -    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
> > +    assert(QEMU_IS_ALIGNED(offset, BDRV_SECTOR_SIZE));
> > +    assert(QEMU_IS_ALIGNED(bytes, BDRV_SECTOR_SIZE));
> >
> >      buf = g_try_malloc(bytes);
> >      if (bytes && buf == NULL) {
> > diff --git a/qemu-img.c b/qemu-img.c
> > index c920e3564c..ca3af0c549 100644
> > --- a/qemu-img.c
> > +++ b/qemu-img.c
> > @@ -2138,7 +2138,7 @@ static int img_convert(int argc, char **argv)
> >              int64_t sval;
> >
> >              sval = cvtnum(optarg);
> > -            if (sval < 0 || sval & (BDRV_SECTOR_SIZE - 1) ||
> > +            if (sval < 0 || !QEMU_IS_ALIGNED(sval, BDRV_SECTOR_SIZE) ||
> >                  sval / BDRV_SECTOR_SIZE > MAX_BUF_SECTORS) {
> >                  error_report("Invalid buffer size for sparse output
> specified. "
> >                      "Valid sizes are multiples of %llu up to %llu.
> Select "
> >
>
>
>