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bitmap: add atomic test and clear
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 <stefanha@redhat.com> Message-Id: <1417519399-3166-3-git-send-email-stefanha@redhat.com> [Test before xchg; then a full barrier is needed at the end just like in the previous patch. The barrier can be avoided if we did at least one xchg. - Paolo] Reviewed-by: Fam Zheng <famz@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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@ -41,6 +41,7 @@
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* bitmap_set(dst, pos, nbits) Set specified bit area
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* bitmap_set_atomic(dst, pos, nbits) Set specified bit area with atomic ops
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* bitmap_clear(dst, pos, nbits) Clear specified bit area
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* bitmap_test_and_clear_atomic(dst, pos, nbits) Test and clear area
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* bitmap_find_next_zero_area(buf, len, pos, n, mask) Find bit free area
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*/
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@ -229,6 +230,7 @@ static inline int bitmap_intersects(const unsigned long *src1,
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void bitmap_set(unsigned long *map, long i, long len);
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void bitmap_set_atomic(unsigned long *map, long i, long len);
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void bitmap_clear(unsigned long *map, long start, long nr);
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bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr);
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unsigned long bitmap_find_next_zero_area(unsigned long *map,
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unsigned long size,
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unsigned long start,
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@ -235,6 +235,51 @@ void bitmap_clear(unsigned long *map, long start, long nr)
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}
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}
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bool bitmap_test_and_clear_atomic(unsigned long *map, long start, long nr)
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{
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unsigned long *p = map + BIT_WORD(start);
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const long size = start + nr;
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int bits_to_clear = BITS_PER_LONG - (start % BITS_PER_LONG);
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unsigned long mask_to_clear = BITMAP_FIRST_WORD_MASK(start);
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unsigned long dirty = 0;
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unsigned long old_bits;
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/* First word */
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if (nr - bits_to_clear > 0) {
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old_bits = atomic_fetch_and(p, ~mask_to_clear);
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dirty |= old_bits & mask_to_clear;
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nr -= bits_to_clear;
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bits_to_clear = BITS_PER_LONG;
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mask_to_clear = ~0UL;
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p++;
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}
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/* Full words */
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if (bits_to_clear == BITS_PER_LONG) {
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while (nr >= BITS_PER_LONG) {
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if (*p) {
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old_bits = atomic_xchg(p, 0);
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dirty |= old_bits;
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}
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nr -= BITS_PER_LONG;
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p++;
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}
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}
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/* Last word */
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if (nr) {
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mask_to_clear &= BITMAP_LAST_WORD_MASK(size);
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old_bits = atomic_fetch_and(p, ~mask_to_clear);
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dirty |= old_bits & mask_to_clear;
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} else {
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if (!dirty) {
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smp_mb();
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}
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}
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return dirty != 0;
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}
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#define ALIGN_MASK(x,mask) (((x)+(mask))&~(mask))
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/**
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