Patchwork [v3,1/9] string: introduce memweight

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Submitter Akinobu Mita
Date June 9, 2012, 12:50 a.m.
Message ID <1339203038-13069-1-git-send-email-akinobu.mita@gmail.com>
Download mbox | patch
Permalink /patch/163875/
State Not Applicable
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Comments

Akinobu Mita - June 9, 2012, 12:50 a.m.
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(-)
Tony Luck - June 20, 2012, 11:12 p.m.
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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Akinobu Mita - June 21, 2012, 9:07 a.m.
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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Patch

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);