linux-kernel - Re: [PATCH 5/7] lib: rework bitmap

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Date:   Thu, 9 May 2019 19:26:33 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Amritha Nambiar <amritha.nambiar@...el.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Matthew Wilcox <willy@...radead.org>,
        "Tobin C . Harding" <tobin@...nel.org>,
        Will Deacon <will.deacon@....com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Vineet Gupta <vineet.gupta1@...opsys.com>,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        linux-kernel@...r.kernel.org, Yury Norov <ynorov@...vell.com>,
        Jens Axboe <axboe@...nel.dk>,
        Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: [PATCH 5/7] lib: rework bitmap_parse()

Hi Andy,

Thanks for thorough review.

On Wed, May 08, 2019 at 11:46:32AM +0300, Andy Shevchenko wrote:
> On Tue, Apr 30, 2019 at 06:06:34PM -0700, Yury Norov wrote:
> > bitmap_parse() is ineffective and full of opaque variables and opencoded
> > parts. It leads to hard understanding and usage of it. This rework
> > includes:
> >  - remove bitmap_shift_left() call from the cycle. Now it makes the
> >    complexity of the algorithm as O(nbits^2). In the suggested approach
> >    the input string is parsed in reverse direction, so no shifts needed;
> >  - relax requirement on a single comma and no white spaces between chunks.
> >    It is considered useful in scripting, and it aligns with
> >    bitmap_parselist();
> >  - split bitmap_parse() to small readable helpers;
> >  - make an explicit calculation of the end of input line at the
> >    beginning, so users of the bitmap_parse() won't bother doing this.
> 
> > +static inline bool in_str(const char *start, const char *ptr)
> > +{
> > +	return start <= ptr;
> > +}
> > +
> 
> The explicit use of the conditional is better.
> 
> -- 
> With Best Regards,
> Andy Shevchenko

I still think that is_str() is more verbose, but it's minor issue
anyways, so I obey. Below is the patch that removes the function.
It's up to Andrew finally, either apply it or not.

Thanks,
Yury

>From 7438c15a0b165032a3e5a6d87daabe877dc8cbc8 Mon Sep 17 00:00:00 2001
From: Yury Norov <ynorov@...vell.com>
Date: Thu, 9 May 2019 17:54:23 -0700
Subject: [PATCH] lib: opencode in_str()

Signed-off-by: Yury Norov <ynorov@...vell.com>
---
 lib/bitmap.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/lib/bitmap.c b/lib/bitmap.c
index ebcf4700ebed..ecf93d2982a5 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -454,11 +454,6 @@ static inline bool end_of_region(char c)
 	return __end_of_region(c) || end_of_str(c);
 }
 
-static inline bool in_str(const char *start, const char *ptr)
-{
-	return start <= ptr;
-}
-
 /*
  * The format allows commas and whitespases at the beginning
  * of the region.
@@ -473,7 +468,7 @@ static const char *bitmap_find_region(const char *str)
 
 static const char *bitmap_find_region_reverse(const char *start, const char *end)
 {
-	while (in_str(start, end) && __end_of_region(*end))
+	while (start <= end && __end_of_region(*end))
 		end--;
 
 	return end;
@@ -618,7 +613,7 @@ static const char *bitmap_get_x32_reverse(const char *start,
 
 		ret |= c << i;
 
-		if (!in_str(start, end) || __end_of_region(*end))
+		if (start > end || __end_of_region(*end))
 			goto out;
 	}
 
@@ -653,7 +648,7 @@ int bitmap_parse(const char *start, unsigned int buflen,
 	u32 *bitmap = (u32 *)maskp;
 	int unset_bit;
 
-	while (in_str(start, (end = bitmap_find_region_reverse(start, end)))) {
+	while (start <= (end = bitmap_find_region_reverse(start, end))) {
 		if (!chunks--)
 			return -EOVERFLOW;
 
-- 
2.17.1