[PATCH v1 3/6] perf: Add an iterator for AUX data

[Alexander Shishkin]

A helper function to sequentially walk through the AUX buffer with a
given callback. This is useful to copy the AUX data out of its buffer.

Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
---
 kernel/events/internal.h    |  5 +++++
 kernel/events/ring_buffer.c | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index 6dc725a7e7bc..eb6cd6b370f9 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -56,6 +56,9 @@ struct ring_buffer {
 	void				*data_pages[0];
 };
 
+typedef unsigned long (*aux_copyfn)(void *data, const void *src,
+				    unsigned long len);
+
 extern void rb_free(struct ring_buffer *rb);
 
 static inline void rb_free_rcu(struct rcu_head *rcu_head)
@@ -80,6 +83,8 @@ extern void perf_event_wakeup(struct perf_event *event);
 extern int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event,
 			pgoff_t pgoff, int nr_pages, long watermark, int flags);
 extern void rb_free_aux(struct ring_buffer *rb);
+extern long rb_output_aux(struct ring_buffer *rb, unsigned long from,
+			  unsigned long to, aux_copyfn copyfn, void *data);
 extern struct ring_buffer *ring_buffer_get(struct perf_event *event);
 extern void ring_buffer_put(struct ring_buffer *rb);
 
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 141aa2ca8728..d6157143f054 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -519,6 +519,40 @@ void *perf_get_aux(struct perf_output_handle *handle)
 }
 EXPORT_SYMBOL_GPL(perf_get_aux);
 
+/*
+ * Copy out AUX data from a ring_buffer using a supplied callback.
+ */
+long rb_output_aux(struct ring_buffer *rb, unsigned long from,
+		   unsigned long to, aux_copyfn copyfn, void *data)
+{
+	unsigned long tocopy, remainder, len = 0;
+	void *addr;
+
+	from &= (rb->aux_nr_pages << PAGE_SHIFT) - 1;
+	to &= (rb->aux_nr_pages << PAGE_SHIFT) - 1;
+
+	do {
+		tocopy = PAGE_SIZE - offset_in_page(from);
+		if (to > from)
+			tocopy = min(tocopy, to - from);
+		if (!tocopy)
+			break;
+
+		addr = rb->aux_pages[from >> PAGE_SHIFT];
+		addr += offset_in_page(from);
+
+		remainder = copyfn(data, addr, tocopy);
+		if (remainder)
+			return -EFAULT;
+
+		len += tocopy;
+		from += tocopy;
+		from &= (rb->aux_nr_pages << PAGE_SHIFT) - 1;
+	} while (to != from);
+
+	return len;
+}
+
 #define PERF_AUX_GFP	(GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY)
 
 static struct page *rb_alloc_aux_page(int node, int order)
-- 
2.17.1