2021-05-25 08:37:15

by Wu Bo

Subject: [PATCH 1/2] crypto: af_alg - use DIV_ROUND_UP helper macro for calculations

From: Wu Bo <[email protected]>

Replace open coded divisor calculations with the DIV_ROUND_UP kernel
macro for better readability.

Signed-off-by: Wu Bo <[email protected]>
---
crypto/af_alg.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/af_alg.c b/crypto/af_alg.c
index 18cc82d..8bd288d 100644
--- a/crypto/af_alg.c
+++ b/crypto/af_alg.c
@@ -411,7 +411,7 @@ int af_alg_make_sg(struct af_alg_sgl *sgl, struct iov_iter *iter, int len)
if (n < 0)
return n;

- npages = (off + n + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ npages = DIV_ROUND_UP(off + n, PAGE_SIZE);
if (WARN_ON(npages == 0))
return -EINVAL;
/* Add one extra for linking */
--
1.8.3.1

2021-05-25 08:53:48

by Christophe Leroy

Subject: Re: [PATCH 1/2] crypto: af_alg - use DIV_ROUND_UP helper macro for calculations

Wu Bo <[email protected]> a écrit :

> From: Wu Bo <[email protected]>
>
> Replace open coded divisor calculations with the DIV_ROUND_UP kernel
> macro for better readability.
>
> Signed-off-by: Wu Bo <[email protected]>
> ---
> crypto/af_alg.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/crypto/af_alg.c b/crypto/af_alg.c
> index 18cc82d..8bd288d 100644
> --- a/crypto/af_alg.c
> +++ b/crypto/af_alg.c
> @@ -411,7 +411,7 @@ int af_alg_make_sg(struct af_alg_sgl *sgl,
> struct iov_iter *iter, int len)
> if (n < 0)
> return n;
>
> - npages = (off + n + PAGE_SIZE - 1) >> PAGE_SHIFT;
> + npages = DIV_ROUND_UP(off + n, PAGE_SIZE);

You should use PFN_UP()

> if (WARN_ON(npages == 0))
> return -EINVAL;
> /* Add one extra for linking */
> --
> 1.8.3.1

2021-05-26 08:32:28

by Dave Chinner

Subject: Re: [PATCH 1/2] crypto: af_alg - use DIV_ROUND_UP helper macro for calculations

On Tue, May 25, 2021 at 10:37:44AM +0200, Christophe Leroy wrote:
> Wu Bo <[email protected]> a ?crit?:
>
> > From: Wu Bo <[email protected]>
> >
> > Replace open coded divisor calculations with the DIV_ROUND_UP kernel
> > macro for better readability.
> >
> > Signed-off-by: Wu Bo <[email protected]>
> > ---
> > crypto/af_alg.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/crypto/af_alg.c b/crypto/af_alg.c
> > index 18cc82d..8bd288d 100644
> > --- a/crypto/af_alg.c
> > +++ b/crypto/af_alg.c
> > @@ -411,7 +411,7 @@ int af_alg_make_sg(struct af_alg_sgl *sgl, struct
> > iov_iter *iter, int len)
> > if (n < 0)
> > return n;
> >
> > - npages = (off + n + PAGE_SIZE - 1) >> PAGE_SHIFT;
> > + npages = DIV_ROUND_UP(off + n, PAGE_SIZE);
>
> You should use PFN_UP()

No. We are not using pfns here - we're converting a byte count to a
page count.

Besides, "PFN_UP" is a horrible, awful api. It does not decribe what
it does and anyone who is not a mm developer will look at it and ask
"what <the ....> does this do?" and have to go looking for it's
definition to determine what it does. Yes, that's exactyl what I've
just done, and I really wish I didn't because, well, it just
reinforces how much we suck at APIs...

OTOH, what DIV_ROUND_UP() does is obvious, widely understood, self
documenting and easy to determine if the usage is correct, which
indeed this is.

The lesson: do not use whacky obscure, out of context macros when a
simple, obvious, widely known macro will give the same result and
make the code easier to understand.

Cheers,

Dave.
--
Dave Chinner
[email protected]