misc-kernel-hacking-hints.md

Miscellaneous kernel hacking hints

The following hints may be useful to folks who are new to kernel development.

Using ccache

Enabling ccache can really help speed up your kernel builds, as well as xfstests builds. I strongly recommend it.

Examples of using ftrace

This is an example of how to debug the lazytime feature (which is when you mount a file system using -m lazytime using a 4.0-rcX and later kernels).

    cd /sys/kernel/debug/tracing
    echo 1 > events/writeback/writeback_lazytime/enable
    echo 1 > events/writeback/writeback_lazytime_iput/enable
    echo "state & 2048" > events/writeback/writeback_dirty_inode_enqueue/filter
    echo 1 > events/writeback/writeback_dirty_inode_enqueue/enable
    echo 1 > events/ext4/ext4_other_inode_update_time/enable
    cat trace_pipe

The definition of the tracepoints can be found in include/linux/trace/events. The tracepoints used by ext4 and be found in ext4.h, and by jbd2 in the jbd2.h files in that directory, and so on.

For more information, please see:

• http://lwn.net/Articles/365835/
• http://lwn.net/Articles/366796/
• http://lwn.net/Articles/370423/