On Fri, 2019-08-02 at 21:18 -0700, Jens Axboe wrote: > On 8/1/19 6:00 PM, Leonardo Bras wrote: > > Applies some bits.h macros in order to improve readability of > > linux/blk_types.h. > > > > Signed-off-by: Leonardo Bras <leona...@linux.ibm.com> > > --- > > include/linux/blk_types.h | 55 ++++++++++++++++++++------------------- > > 1 file changed, 28 insertions(+), 27 deletions(-) > > > > diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h > > index 95202f80676c..31c8c6d274f6 100644 > > --- a/include/linux/blk_types.h > > +++ b/include/linux/blk_types.h > > @@ -9,6 +9,7 @@ > > #include <linux/types.h> > > #include <linux/bvec.h> > > #include <linux/ktime.h> > > +#include <linux/bits.h> > > > > struct bio_set; > > struct bio; > > @@ -101,13 +102,13 @@ static inline bool blk_path_error(blk_status_t error) > > #define BIO_ISSUE_SIZE_BITS 12 > > #define BIO_ISSUE_RES_SHIFT (64 - BIO_ISSUE_RES_BITS) > > #define BIO_ISSUE_SIZE_SHIFT (BIO_ISSUE_RES_SHIFT - > > BIO_ISSUE_SIZE_BITS) > > -#define BIO_ISSUE_TIME_MASK ((1ULL << BIO_ISSUE_SIZE_SHIFT) - 1) > > +#define BIO_ISSUE_TIME_MASK GENMASK_ULL(BIO_ISSUE_SIZE_SHIFT - 1, 0) > > Not sure why we even have these helpers, I'd argue that patches like > this HURT readability, not improve it. When I see > > ((1ULL << SOME_SHIFT) - 1) > > I know precisely what that does, whereas I have to think about the other > one, maybe even look it up to be sure. For instance, without looking > now, I have no idea what the second argument is. Looking at the git log, > I see numerous instances of: > > "xxx: Fix misuses of GENMASK macro > > Arguments are supposed to be ordered high then low." > > Hence it seems GENMASK_ULL is easy to misuse or get wrong, the very > opposite of what you'd want in a helper. How is it helping readability > if the helper is easy to misuse? > > Ditto with > > (1ULL << SOME_SHIFT) > > vs BIT_ULL. But at least that one doesn't have a mysterious 2nd > argument. > > Hence I'm not inclined to apply this patch. >
Well, as a newbie, macros like GENMASK(a,b) look way simpler. I to read than (((1 << a) - 1) << b), or (~((1 << c) - 1)). I mean, in GENMASK all bits >= a, <=b are set. But I agree that once you get used to reading masks created with <<, it doesn't look that harder. Well, thanks for this feedback. Regards, Leonardo Brás
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