The bitmap_onto() function translates one bitmap relative to another but
no function are present to perform the reverse translation.
Introduce bitmap_off() to fill this hole.
Signed-off-by: Herve Codina <herve.cod...@bootlin.com>
---
include/linux/bitmap.h | 3 +++
lib/bitmap.c | 42 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 99451431e4d6..5ecfcbbc91f4 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -65,6 +65,7 @@ struct device;
* bitmap_remap(dst, src, old, new, nbits) *dst = map(old, new)(src)
* bitmap_bitremap(oldbit, old, new, nbits) newbit = map(old, new)(oldbit)
* bitmap_onto(dst, orig, relmap, nbits) *dst = orig relative to relmap
+ * bitmap_off(dst, orig, relmap, nbits) *dst = bitmap_onto() reverse
operation
* bitmap_fold(dst, orig, sz, nbits) dst bits = orig bits mod sz
* bitmap_parse(buf, buflen, dst, nbits) Parse bitmap dst from kernel
buf
* bitmap_parse_user(ubuf, ulen, dst, nbits) Parse bitmap dst from user buf
@@ -208,6 +209,8 @@ int bitmap_bitremap(int oldbit,
const unsigned long *old, const unsigned long *new, int bits);
void bitmap_onto(unsigned long *dst, const unsigned long *orig,
const unsigned long *relmap, unsigned int bits);
+void bitmap_off(unsigned long *dst, const unsigned long *orig,
+ const unsigned long *relmap, unsigned int bits);
void bitmap_fold(unsigned long *dst, const unsigned long *orig,
unsigned int sz, unsigned int nbits);
diff --git a/lib/bitmap.c b/lib/bitmap.c
index 2feccb5047dc..71343967335e 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -682,6 +682,48 @@ void bitmap_onto(unsigned long *dst, const unsigned long
*orig,
}
EXPORT_SYMBOL(bitmap_onto);
+/**
+ * bitmap_off - revert operation done by bitmap_onto()
+ * @dst: resulting translated bitmap
+ * @orig: original untranslated bitmap
+ * @relmap: bitmap relative to which translated
+ * @bits: number of bits in each of these bitmaps
+ *
+ * Suppose onto computed using bitmap_onto(onto, src, relmap, n)
+ * The operation bitmap_off(result, onto, relmap, n) leads to a
+ * result equal or equivalent to src.
+ *
+ * The result can be 'equivalent' because bitmap_onto() and
+ * bitmap_off() are not bijective.
+ * The result and src values are equivalent in that sense that a
+ * call to bitmap_onto(onto, src, relmap, n) and a call to
+ * bitmap_onto(onto, result, relmap, n) will lead to the same onto
+ * value.
+ *
+ * If either of @orig or @relmap is empty (no set bits), then @dst
+ * will be returned empty.
+ *
+ * All bits in @dst not set by the above rule are cleared.
+ */
+void bitmap_off(unsigned long *dst, const unsigned long *orig,
+ const unsigned long *relmap, unsigned int bits)
+{
+ unsigned int n, m; /* same meaning as in above comment */
+
+ if (dst == orig) /* following doesn't handle inplace mappings */
+ return;
+ bitmap_zero(dst, bits);
+
+ m = 0;
+ for_each_set_bit(n, relmap, bits) {
+ /* m == bitmap_pos_to_ord(relmap, n, bits) */
+ if (test_bit(n, orig))
+ set_bit(m, dst);
+ m++;
+ }
+}
+EXPORT_SYMBOL(bitmap_off);
+
#ifdef CONFIG_NUMA
/**
* bitmap_fold - fold larger bitmap into smaller, modulo specified size
--
2.43.0
