linux-kernel - [PATCH v2 2/3] lib/find_bit: create find_first_zero_bit

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Date:   Tue, 23 Aug 2022 18:26:23 -0700
From:   Yury Norov <yury.norov@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Cc:     Yury Norov <yury.norov@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Dennis Zhou <dennis@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Alexey Klimov <aklimov@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Andy Whitcroft <apw@...onical.com>
Subject: [PATCH v2 2/3] lib/find_bit: create find_first_zero_bit_le()

find_first_zero_bit_le() is an alias to find_next_zero_bit_le(),
despite that 'next' is known to be slower than the 'first' version.

Now that we have a common FIND_FIRST_BIT() macro helper, it's trivial
to implement find_first_zero_bit_le() as a real function.

Moving find_*_le() to a separate file helps to fit the FIND_FIRST_BIT()
to the _le needs by wiring word_op to swab.

Signed-off-by: Yury Norov <yury.norov@...il.com>
---
Like other find_*_le() functions, the new one takes void *addr, instead
of unsigned long *. This should be fixed for all in a separate series.

 MAINTAINERS          |  1 +
 include/linux/find.h | 23 ++++++++++++++++++-----
 lib/Makefile         |  1 +
 lib/find_bit_be.c    | 23 +++++++++++++++++++++++
 4 files changed, 43 insertions(+), 5 deletions(-)
 create mode 100644 lib/find_bit_be.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 02e11f2dbafe..fd1d1625b053 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3614,6 +3614,7 @@ F:	lib/bitmap.c
 F:	lib/cpumask.c
 F:	lib/find_bit.h
 F:	lib/find_bit.c
+F:	lib/find_bit_le.c
 F:	lib/find_bit_benchmark.c
 F:	lib/test_bitmap.c
 F:	tools/include/linux/bitmap.h
diff --git a/include/linux/find.h b/include/linux/find.h
index 424ef67d4a42..2464bff5de04 100644
--- a/include/linux/find.h
+++ b/include/linux/find.h
@@ -17,6 +17,10 @@ extern unsigned long _find_first_and_bit(const unsigned long *addr1,
 extern unsigned long _find_first_zero_bit(const unsigned long *addr, unsigned long size);
 extern unsigned long _find_last_bit(const unsigned long *addr, unsigned long size);
 
+#ifdef __BIG_ENDIAN
+unsigned long _find_first_zero_bit_le(const unsigned long *addr, unsigned long size);
+#endif
+
 #ifndef find_next_bit
 /**
  * find_next_bit - find the next set bit in a memory region
@@ -251,6 +255,20 @@ unsigned long find_next_zero_bit_le(const void *addr, unsigned
 }
 #endif
 
+#ifndef find_first_zero_bit_le
+static inline
+unsigned long find_first_zero_bit_le(const void *addr, unsigned long size)
+{
+	if (small_const_nbits(size)) {
+		unsigned long val = swab(*(const unsigned long *)addr) | ~GENMASK(size - 1, 0);
+
+		return val == ~0UL ? size : ffz(val);
+	}
+
+	return _find_first_zero_bit_le(addr, size);
+}
+#endif
+
 #ifndef find_next_bit_le
 static inline
 unsigned long find_next_bit_le(const void *addr, unsigned
@@ -270,11 +288,6 @@ unsigned long find_next_bit_le(const void *addr, unsigned
 }
 #endif
 
-#ifndef find_first_zero_bit_le
-#define find_first_zero_bit_le(addr, size) \
-	find_next_zero_bit_le((addr), (size), 0)
-#endif
-
 #else
 #error "Please fix <asm/byteorder.h>"
 #endif
diff --git a/lib/Makefile b/lib/Makefile
index 5927d7fa0806..0f41b76a277e 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -49,6 +49,7 @@ obj-y += bcd.o sort.o parser.o debug_locks.o random32.o \
 	 percpu-refcount.o rhashtable.o base64.o \
 	 once.o refcount.o usercopy.o errseq.o bucket_locks.o \
 	 generic-radix-tree.o
+obj-$(CONFIG_CPU_BIG_ENDIAN) += find_bit_be.o
 obj-$(CONFIG_STRING_SELFTEST) += test_string.o
 obj-y += string_helpers.o
 obj-$(CONFIG_TEST_STRING_HELPERS) += test-string_helpers.o
diff --git a/lib/find_bit_be.c b/lib/find_bit_be.c
new file mode 100644
index 000000000000..36173cb7e012
--- /dev/null
+++ b/lib/find_bit_be.c
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Big-endian routines for bit search */
+
+#include <linux/bitops.h>
+#include <linux/bitmap.h>
+#include <linux/export.h>
+#include <linux/math.h>
+#include <linux/minmax.h>
+#include <linux/swab.h>
+
+#define word_op swab
+#include "find_bit.h"
+
+#ifndef find_first_zero_bit_le
+/*
+ * Find the first cleared bit in an LE memory region.
+ */
+unsigned long _find_first_zero_bit_le(const unsigned long *addr, unsigned long size)
+{
+	return FIND_FIRST_BIT(~addr[idx], size);
+}
+EXPORT_SYMBOL(_find_first_zero_bit_le);
+#endif
-- 
2.34.1