[PATCH v3 1/9] string: introduce memweight

[PATCH v3 1/9] string: introduce memweight

[Akinobu Mita]

memweight() is the function that counts the total number of bits set
in memory area.  Unlike bitmap_weight(), memweight() takes pointer
and size in bytes to specify a memory area which does not need to be
aligned to long-word boundary.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Anders Larsen <al@alarsen.net>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: dm-devel@redhat.com
Cc: linux-fsdevel@vger.kernel.org
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: linux-media@vger.kernel.org
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: ocfs2-devel@oss.oracle.com
Cc: Jan Kara <jack@suse.cz>
Cc: linux-ext4@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Matthew Wilcox <matthew@wil.cx>
---
v3: add comment for the last loop, adviced by Jan Kara
v2: simplify memweight(), adviced by Jan Kara

 include/linux/string.h |    3 +++
 lib/string.c           |   36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 0 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index e033564..ffe0442 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -145,4 +145,7 @@ static inline bool strstarts(const char *str, const char *prefix)
 	return strncmp(str, prefix, strlen(prefix)) == 0;
 }
 #endif
+
+extern size_t memweight(const void *ptr, size_t bytes);
+
 #endif /* _LINUX_STRING_H_ */
diff --git a/lib/string.c b/lib/string.c
index e5878de..e467186 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -26,6 +26,7 @@
 #include <linux/export.h>
 #include <linux/bug.h>
 #include <linux/errno.h>
+#include <linux/bitmap.h>
 
 #ifndef __HAVE_ARCH_STRNICMP
 /**
@@ -824,3 +825,38 @@ void *memchr_inv(const void *start, int c, size_t bytes)
 	return check_bytes8(start, value, bytes % 8);
 }
 EXPORT_SYMBOL(memchr_inv);
+
+/**
+ * memweight - count the total number of bits set in memory area
+ * @ptr: pointer to the start of the area
+ * @bytes: the size of the area
+ */
+size_t memweight(const void *ptr, size_t bytes)
+{
+	size_t w = 0;
+	size_t longs;
+	const unsigned char *bitmap = ptr;
+
+	for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
+			bytes--, bitmap++)
+		w += hweight8(*bitmap);
+
+	longs = bytes / sizeof(long);
+	if (longs) {
+		BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
+		w += bitmap_weight((unsigned long *)bitmap,
+				longs * BITS_PER_LONG);
+		bytes -= longs * sizeof(long);
+		bitmap += longs * sizeof(long);
+	}
+	/*
+	 * The reason that this last loop is distinct from the preceding
+	 * bitmap_weight() call is to compute 1-bits in the last region smaller
+	 * than sizeof(long) properly on big-endian systems.
+	 */
+	for (; bytes > 0; bytes--, bitmap++)
+		w += hweight8(*bitmap);
+
+	return w;
+}
+EXPORT_SYMBOL(memweight);
-- 
1.7.7.6

[PATCH v3 4/9] affs: use memweight()

[Akinobu Mita]

Use memweight() to count the total number of bits set in memory area.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: linux-fsdevel@vger.kernel.org
---
No changes from v1

 fs/affs/bitmap.c |   28 ++--------------------------
 1 files changed, 2 insertions(+), 26 deletions(-)

diff --git a/fs/affs/bitmap.c b/fs/affs/bitmap.c
index 3e26271..3dfdcd2 100644
--- a/fs/affs/bitmap.c
+++ b/fs/affs/bitmap.c
@@ -10,30 +10,6 @@
 #include <linux/slab.h>
 #include "affs.h"
 
-/* This is, of course, shamelessly stolen from fs/minix */
-
-static const int nibblemap[] = { 0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4 };
-
-static u32
-affs_count_free_bits(u32 blocksize, const void *data)
-{
-	const u32 *map;
-	u32 free;
-	u32 tmp;
-
-	map = data;
-	free = 0;
-	for (blocksize /= 4; blocksize > 0; blocksize--) {
-		tmp = *map++;
-		while (tmp) {
-			free += nibblemap[tmp & 0xf];
-			tmp >>= 4;
-		}
-	}
-
-	return free;
-}
-
 u32
 affs_count_free_blocks(struct super_block *sb)
 {
@@ -317,7 +293,7 @@ int affs_init_bitmap(struct super_block *sb, int *flags)
 			goto out;
 		}
 		pr_debug("AFFS: read bitmap block %d: %d\n", blk, bm->bm_key);
-		bm->bm_free = affs_count_free_bits(sb->s_blocksize - 4, bh->b_data + 4);
+		bm->bm_free = memweight(bh->b_data + 4, sb->s_blocksize - 4);
 
 		/* Don't try read the extension if this is the last block,
 		 * but we also need the right bm pointer below
@@ -367,7 +343,7 @@ int affs_init_bitmap(struct super_block *sb, int *flags)
 
 	/* recalculate bitmap count for last block */
 	bm--;
-	bm->bm_free = affs_count_free_bits(sb->s_blocksize - 4, bh->b_data + 4);
+	bm->bm_free = memweight(bh->b_data + 4, sb->s_blocksize - 4);
 
 out:
 	affs_brelse(bh);
-- 
1.7.7.6

Re: [PATCH v3 1/9] string: introduce memweight

[Andrew Morton]

On Sat,  9 Jun 2012 09:50:30 +0900
Akinobu Mita <akinobu.mita@gmail.com> wrote:

> memweight() is the function that counts the total number of bits set
> in memory area.  Unlike bitmap_weight(), memweight() takes pointer
> and size in bytes to specify a memory area which does not need to be
> aligned to long-word boundary.
> 
> ...
>
> +/**
> + * memweight - count the total number of bits set in memory area
> + * @ptr: pointer to the start of the area
> + * @bytes: the size of the area
> + */
> +size_t memweight(const void *ptr, size_t bytes)
> +{
> +	size_t w = 0;

Calling the return value "ret" is a useful convention and fits well here.

> +	size_t longs;
> +	const unsigned char *bitmap = ptr;
> +
> +	for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
> +			bytes--, bitmap++)
> +		w += hweight8(*bitmap);
> +
> +	longs = bytes / sizeof(long);
> +	if (longs) {
> +		BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
> +		w += bitmap_weight((unsigned long *)bitmap,
> +				longs * BITS_PER_LONG);
> +		bytes -= longs * sizeof(long);
> +		bitmap += longs * sizeof(long);
> +	}
> +	/*
> +	 * The reason that this last loop is distinct from the preceding
> +	 * bitmap_weight() call is to compute 1-bits in the last region smaller
> +	 * than sizeof(long) properly on big-endian systems.
> +	 */
> +	for (; bytes > 0; bytes--, bitmap++)
> +		w += hweight8(*bitmap);
> +
> +	return w;
> +}
> +EXPORT_SYMBOL(memweight);

diff -puN lib/string.c~string-introduce-memweight-fix lib/string.c
--- a/lib/string.c~string-introduce-memweight-fix
+++ a/lib/string.c
@@ -833,18 +833,18 @@ EXPORT_SYMBOL(memchr_inv);
  */
 size_t memweight(const void *ptr, size_t bytes)
 {
-	size_t w = 0;
+	size_t ret = 0;
 	size_t longs;
 	const unsigned char *bitmap = ptr;
 
 	for (; bytes > 0 && ((unsigned long)bitmap) % sizeof(long);
 			bytes--, bitmap++)
-		w += hweight8(*bitmap);
+		ret += hweight8(*bitmap);
 
 	longs = bytes / sizeof(long);
 	if (longs) {
 		BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
-		w += bitmap_weight((unsigned long *)bitmap,
+		ret += bitmap_weight((unsigned long *)bitmap,
 				longs * BITS_PER_LONG);
 		bytes -= longs * sizeof(long);
 		bitmap += longs * sizeof(long);
@@ -855,8 +855,8 @@ size_t memweight(const void *ptr, size_t
 	 * than sizeof(long) properly on big-endian systems.
 	 */
 	for (; bytes > 0; bytes--, bitmap++)
-		w += hweight8(*bitmap);
+		ret += hweight8(*bitmap);
 
-	return w;
+	return ret;
 }
 EXPORT_SYMBOL(memweight);
_

Re: [PATCH v3 1/9] string: introduce memweight

[Tony Luck]

On Fri, Jun 8, 2012 at 5:50 PM, Akinobu Mita <akinobu.mita@gmail.com> wrote:
>  lib/string.c           |   36 ++++++++++++++++++++++++++++++++++++

Is lib/string.c the right place for this?  I get a build error on the
ia64 sim_defconfig:

  LD      arch/ia64/hp/sim/boot/bootloader

It fails because it pulls in lib/lib.a(string.o) to get some
innocuous function like strcpy() ... but it also gets
given memweight() which relies on __bitmap_weight()
which it doesn't have, because it doesn't include lib/built-in.o
(which is where bitmap.o, the definer of __bitmap_weight(), has
been linked).

Moving memweight() to lib/bitmap.c fixes the problem. But it
isn't really clear that it belongs there either.  Perhaps it should
be its own file lib/memweight.c that gets included in lib/lib.a?

-Tony
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Re: [PATCH v3 1/9] string: introduce memweight

[Akinobu Mita]

2012/6/21 Tony Luck <tony.luck@gmail.com>:
> On Fri, Jun 8, 2012 at 5:50 PM, Akinobu Mita <akinobu.mita@gmail.com> wrote:
>>  lib/string.c           |   36 ++++++++++++++++++++++++++++++++++++
>
> Is lib/string.c the right place for this?  I get a build error on the
> ia64 sim_defconfig:
>
>  LD      arch/ia64/hp/sim/boot/bootloader
>
> It fails because it pulls in lib/lib.a(string.o) to get some
> innocuous function like strcpy() ... but it also gets
> given memweight() which relies on __bitmap_weight()
> which it doesn't have, because it doesn't include lib/built-in.o
> (which is where bitmap.o, the definer of __bitmap_weight(), has
> been linked).
>
> Moving memweight() to lib/bitmap.c fixes the problem. But it
> isn't really clear that it belongs there either.  Perhaps it should
> be its own file lib/memweight.c that gets included in lib/lib.a?

I'll fix it by making lib/memweight.c as you suggested.
Thanks for your report and suggestion.
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