[PATCH v4 17/22] perf: Add a helper to copy AUX data in the kernel

[Alexander Shishkin <alexander.shishkin@linux.intel.com>]

This patch adds a helper for the kernel counters that generate AUX data to
copy this data around, for example, to output it to the perf ring buffer
as a sample record or write it to a core dump file.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
 kernel/events/internal.h    |  5 +++++
 kernel/events/ring_buffer.c | 31 +++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index f4cfa4cabb..bb035dd645 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -52,6 +52,9 @@ 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);
 extern struct ring_buffer *
 rb_alloc(int nr_pages, long watermark, int cpu, int flags);
@@ -59,6 +62,8 @@ 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, struct perf_event *event);
+extern long rb_output_aux(struct ring_buffer *rb, unsigned long from,
+			  unsigned long to, aux_copyfn copyfn, void *data);
 extern struct ring_buffer *
 rb_alloc_kernel(struct perf_event *event, int nr_pages, int aux_nr_pages);
 extern void rb_free_kernel(struct ring_buffer *rb, struct perf_event *event);
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 7887601aa5..4cf5a1cd0a 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -345,6 +345,37 @@ void *perf_get_aux(struct perf_output_handle *handle)
 	return handle->rb->aux_priv;
 }
 
+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)
-- 
2.1.0