ring-buffer: use BUF_PAGE_HDR_SIZE in calculating index

The index of the event is found by masking PAGE_MASK to it and
subtracting the header size. Currently the header size is calculate
by PAGE_SIZE - BUF_PAGE_SIZE, when we already have a macro
BUF_PAGE_HDR_SIZE to define it.

If we want to change BUF_PAGE_SIZE to something less than filling
the rest of the page (this is done for debugging), then we break
the algorithm to find the index.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index ed3559944fcf64219454f1fa0ff932886f369fd2..6b17a11e42a24aed7674be4f1b00cf6791797bc6 100644 (file)
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1013,7 +1013,7 @@ rb_event_index(struct ring_buffer_event *event)
 {
        unsigned long addr = (unsigned long)event;
 
-       return (addr & ~PAGE_MASK) - (PAGE_SIZE - BUF_PAGE_SIZE);
+       return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
 }
 
 static inline int