[PATCH V3 02/14] sbitmap: introduce __sbitmap_for_each_set()

[Ming Lei <ming.lei@redhat.com>]

We need to iterate ctx starting from any ctx in round robin
way, so introduce this helper.

Cc: Omar Sandoval <osandov@fb.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/sbitmap.h | 56 ++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 41 insertions(+), 15 deletions(-)

diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index a1904aadbc45..55b4a762c8b7 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -211,10 +211,14 @@ bool sbitmap_any_bit_set(const struct sbitmap *sb);
  */
 bool sbitmap_any_bit_clear(const struct sbitmap *sb);
 
+#define SB_NR_TO_INDEX(sb, bitnr) ((bitnr) >> (sb)->shift)
+#define SB_NR_TO_BIT(sb, bitnr) ((bitnr) & ((1U << (sb)->shift) - 1U))
+
 typedef bool (*sb_for_each_fn)(struct sbitmap *, unsigned int, void *);
 
 /**
  * sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
+ * @start: Where to start the iteration
  * @sb: Bitmap to iterate over.
  * @fn: Callback. Should return true to continue or false to break early.
  * @data: Pointer to pass to callback.
@@ -222,35 +226,57 @@ typedef bool (*sb_for_each_fn)(struct sbitmap *, unsigned int, void *);
  * This is inline even though it's non-trivial so that the function calls to the
  * callback will hopefully get optimized away.
  */
-static inline void sbitmap_for_each_set(struct sbitmap *sb, sb_for_each_fn fn,
-					void *data)
+static inline void __sbitmap_for_each_set(struct sbitmap *sb,
+					  unsigned int start,
+					  sb_for_each_fn fn, void *data)
 {
-	unsigned int i;
+	unsigned int index = SB_NR_TO_INDEX(sb, start);
+	unsigned int nr = SB_NR_TO_BIT(sb, start);
+	unsigned int scanned = 0;
 
-	for (i = 0; i < sb->map_nr; i++) {
-		struct sbitmap_word *word = &sb->map[i];
-		unsigned int off, nr;
+	while (1) {
+		struct sbitmap_word *word = &sb->map[index];
+		unsigned int depth = min_t(unsigned int, word->depth - nr,
+					   sb->depth - scanned);
 
+		scanned += depth;
 		if (!word->word)
-			continue;
+			goto next;
 
-		nr = 0;
-		off = i << sb->shift;
+		depth += nr;
+		start = index << sb->shift;
 		while (1) {
-			nr = find_next_bit(&word->word, word->depth, nr);
-			if (nr >= word->depth)
+			nr = find_next_bit(&word->word, depth, nr);
+			if (nr >= depth)
 				break;
-
-			if (!fn(sb, off + nr, data))
+			if (!fn(sb, start + nr, data))
 				return;
 
 			nr++;
 		}
+ next:
+		if (scanned >= sb->depth)
+			break;
+		nr = 0;
+		if (++index >= sb->map_nr)
+			index = 0;
 	}
 }
 
-#define SB_NR_TO_INDEX(sb, bitnr) ((bitnr) >> (sb)->shift)
-#define SB_NR_TO_BIT(sb, bitnr) ((bitnr) & ((1U << (sb)->shift) - 1U))
+/**
+ * sbitmap_for_each_set() - Iterate over each set bit in a &struct sbitmap.
+ * @sb: Bitmap to iterate over.
+ * @fn: Callback. Should return true to continue or false to break early.
+ * @data: Pointer to pass to callback.
+ *
+ * This is inline even though it's non-trivial so that the function calls to the
+ * callback will hopefully get optimized away.
+ */
+static inline void sbitmap_for_each_set(struct sbitmap *sb, sb_for_each_fn fn,
+					void *data)
+{
+	__sbitmap_for_each_set(sb, 0, fn, data);
+}
 
 static inline unsigned long *__sbitmap_word(struct sbitmap *sb,
 					    unsigned int bitnr)
-- 
2.9.5