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+# Tracing the loop device kernel module
+
+The loop device kernel module can be traced with the *ftrace* framework of the
+Linux kernel. Therefore, *ftrace* must be compiled into the Linux kernel and the
+user space module *trace-cmd* is necessary.
+
+
+## Creating the trace file
+
+Each loop device specific operation can be traced with the following command
+```bash
+trace-cmd record -p function_graph --module loop -o [trace file] [cmd]
+```
+where `[trace file]` is the created trace file and `[cmd]` is one of the
+following loop device operation:
+  * add loop device: `losetup -f test.img`
+  * read from loop device: `dd if=/dev/loop0 bs=512 count=1 of=tmp.img`
+  * write to loop device: `dd of=/dev/loop0 bs=512 count=1 if=tmp.img`
+  * remove loop device: `losetup -D`
+
+
+## Viewing the trace file
+
+The created trace file can be viewed on the command line with the following
+command:
+```bash
+trace-cmd report -i [trace file]
+```
+where `[trace file]` is the already created trace file.