frace docs an mmap minor improvements

ftrace.md

@@ -10,8 +10,6 @@ Trace a single function:
     # Clear previous trace.
     echo '' > trace
 
-    echo 1 > max_graph_depth
-
     # List the available tracers, and pick one.
     cat available_tracers
     echo function > current_tracer
@@ -29,7 +27,7 @@ Trace a single function:
     head trace
 
     # Observe trace continously, and drain seen events out.
-    cat trace_pipe
+    cat trace_pipe &
 
 Sample output:
 
@@ -60,6 +58,7 @@ Sample output:
 
 Trace all possible functions, and draw a call graph:
 
+    echo 1 > max_graph_depth
     echo 1 > events/enable
     echo function_graph > current_tracer
 

kernel_module/mmap.c

@@ -3,10 +3,18 @@ Remember: mmap, like most fops, does not work with debugfs as of 4.9! https://pa
 
 Adapted from:
 https://coherentmusings.wordpress.com/2014/06/10/implementing-mmap-for-transferring-data-from-user-space-to-kernel-space/
+
+Related:
+
+- https://stackoverflow.com/questions/10760479/mmap-kernel-buffer-to-user-space/10770582#10770582
+- https://stackoverflow.com/questions/1623008/allocating-memory-for-user-space-from-kernel-thread
+- https://stackoverflow.com/questions/6967933/mmap-mapping-in-user-space-a-kernel-buffer-allocated-with-kmalloc
+- https://github.com/jeremytrimble/ezdma
+- https://github.com/simonjhall/dma
+- https://github.com/ikwzm/udmabuf
 */
 
 #include <asm/uaccess.h> /* copy_from_user */
-#include <linux/debugfs.h>
 #include <linux/fs.h>
 #include <linux/init.h>
 #include <linux/kernel.h> /* min */