The new bitmap_test_and_clear_atomic() function clears a range and returns whether or not the bits were set.
Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> --- include/qemu/bitmap.h | 2 ++ util/bitmap.c | 37 +++++++++++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+) diff --git a/include/qemu/bitmap.h b/include/qemu/bitmap.h index 3e0a4f3..86dd9cd 100644 --- a/include/qemu/bitmap.h +++ b/include/qemu/bitmap.h @@ -41,6 +41,7 @@ * bitmap_set(dst, pos, nbits) Set specified bit area * bitmap_set_atomic(dst, pos, nbits) Set specified bit area with atomic ops * bitmap_clear(dst, pos, nbits) Clear specified bit area + * bitmap_test_and_clear_atomic(dst, pos, nbits) Test and clear area * bitmap_find_next_zero_area(buf, len, pos, n, mask) Find bit free area */ @@ -229,6 +230,7 @@ static inline int bitmap_intersects(const unsigned long *src1, void bitmap_set(unsigned long *map, long i, long len); void bitmap_set_atomic(unsigned long *map, long i, long len); void bitmap_clear(unsigned long *map, long start, long nr); +bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr); unsigned long bitmap_find_next_zero_area(unsigned long *map, unsigned long size, unsigned long start, diff --git a/util/bitmap.c b/util/bitmap.c index 40db0d9..d297066 100644 --- a/util/bitmap.c +++ b/util/bitmap.c @@ -233,6 +233,43 @@ void bitmap_clear(unsigned long *map, long start, long nr) } } +bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr) +{ + unsigned long *p = map + BIT_WORD(start); + const long size = start + nr; + int bits_to_clear = BITS_PER_LONG - (start % BITS_PER_LONG); + unsigned long mask_to_clear = BITMAP_FIRST_WORD_MASK(start); + unsigned long dirty = 0; + unsigned long old_bits; + + /* First word */ + if (nr - bits_to_clear > 0) { + old_bits = atomic_fetch_and(p, ~mask_to_clear); + dirty |= old_bits & mask_to_clear; + nr -= bits_to_clear; + bits_to_clear = BITS_PER_LONG; + mask_to_clear = ~0UL; + p++; + } + + /* Full words */ + while (nr - bits_to_clear >= 0) { + old_bits = atomic_xchg(p, 0); + dirty |= old_bits; + nr -= bits_to_clear; + p++; + } + + /* Last word */ + if (nr) { + mask_to_clear &= BITMAP_LAST_WORD_MASK(size); + old_bits = atomic_fetch_and(p, ~mask_to_clear); + dirty |= old_bits & mask_to_clear; + } + + return dirty; +} + #define ALIGN_MASK(x,mask) (((x)+(mask))&~(mask)) /** -- 2.1.0