[PATCH v8 21/63] xarray: Add xa_extract

[Matthew Wilcox <willy@infradead.org>]

From: Matthew Wilcox <mawilcox@microsoft.com>

This function combines the functionality of radix_tree_gang_lookup() and
radix_tree_gang_lookup_tagged().  It extracts entries matching the
specified filter into a normal array.

Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
---
 include/linux/xarray.h |  2 ++
 lib/xarray.c           | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 82 insertions(+)

diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index cf7966bfdd3e..85dd909586f0 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -227,6 +227,8 @@ void *xa_find(struct xarray *xa, unsigned long *index,
 		unsigned long max, xa_tag_t) __attribute__((nonnull(2)));
 void *xa_find_after(struct xarray *xa, unsigned long *index,
 		unsigned long max, xa_tag_t) __attribute__((nonnull(2)));
+unsigned int xa_extract(struct xarray *, void **dst, unsigned long start,
+		unsigned long max, unsigned int n, xa_tag_t);
 
 /**
  * xa_init() - Initialise an empty XArray.
diff --git a/lib/xarray.c b/lib/xarray.c
index 267510e98a57..124bbfec66ae 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1388,6 +1388,86 @@ void *xa_find_after(struct xarray *xa, unsigned long *indexp,
 }
 EXPORT_SYMBOL(xa_find_after);
 
+static unsigned int xas_extract_present(struct xa_state *xas, void **dst,
+			unsigned long max, unsigned int n)
+{
+	void *entry;
+	unsigned int i = 0;
+
+	rcu_read_lock();
+	xas_for_each(xas, entry, max) {
+		if (xas_retry(xas, entry))
+			continue;
+		dst[i++] = entry;
+		if (i == n)
+			break;
+	}
+	rcu_read_unlock();
+
+	return i;
+}
+
+static unsigned int xas_extract_tag(struct xa_state *xas, void **dst,
+			unsigned long max, unsigned int n, xa_tag_t tag)
+{
+	void *entry;
+	unsigned int i = 0;
+
+	rcu_read_lock();
+	xas_for_each_tag(xas, entry, max, tag) {
+		if (xas_retry(xas, entry))
+			continue;
+		dst[i++] = entry;
+		if (i == n)
+			break;
+	}
+	rcu_read_unlock();
+
+	return i;
+}
+
+/**
+ * xa_extract() - Copy selected entries from the XArray into a normal array.
+ * @xa: The source XArray to copy from.
+ * @dst: The buffer to copy entries into.
+ * @start: The first index in the XArray eligible to be selected.
+ * @max: The last index in the XArray eligible to be selected.
+ * @n: The maximum number of entries to copy.
+ * @filter: Selection criterion.
+ *
+ * Copies up to @n entries that match @filter from the XArray.  The
+ * copied entries will have indices between @start and @max, inclusive.
+ *
+ * The @filter may be an XArray tag value, in which case entries which are
+ * tagged with that tag will be copied.  It may also be %XA_PRESENT, in
+ * which case non-NULL entries will be copied.
+ *
+ * The entries returned may not represent a snapshot of the XArray at a
+ * moment in time.  For example, if another thread stores to index 5, then
+ * index 10, calling xa_extract() may return the old contents of index 5
+ * and the new contents of index 10.  Indices not modified while this
+ * function is running will not be skipped.
+ *
+ * If you need stronger guarantees, holding the xa_lock across calls to this
+ * function will prevent concurrent modification.
+ *
+ * Context: Any context.  Takes and releases the RCU lock.
+ * Return: The number of entries copied.
+ */
+unsigned int xa_extract(struct xarray *xa, void **dst, unsigned long start,
+			unsigned long max, unsigned int n, xa_tag_t filter)
+{
+	XA_STATE(xas, xa, start);
+
+	if (!n)
+		return 0;
+
+	if ((__force unsigned int)filter < XA_MAX_TAGS)
+		return xas_extract_tag(&xas, dst, max, n, filter);
+	return xas_extract_present(&xas, dst, max, n);
+}
+EXPORT_SYMBOL(xa_extract);
+
 #ifdef XA_DEBUG
 void xa_dump_node(const struct xa_node *node)
 {
-- 
2.16.1