debugfs

Debug-only interface - not for production use by applications.

Creating debugfs Files

#include <linux/debugfs.h>

struct my_dev {
    struct dentry *debugfs_dir;
    u32 debug_counter;
    bool debug_flag;
};

static int my_probe(struct platform_device *pdev)
{
    struct my_dev *dev;

    /* Create directory */
    dev->debugfs_dir = debugfs_create_dir("my_driver", NULL);

    /* Simple integer file */
    debugfs_create_u32("counter", 0644, dev->debugfs_dir,
                       &dev->debug_counter);

    /* Boolean file (Y/N) */
    debugfs_create_bool("enabled", 0644, dev->debugfs_dir,
                        &dev->debug_flag);

    return 0;
}

static void my_remove(struct platform_device *pdev)
{
    struct my_dev *dev = platform_get_drvdata(pdev);

    debugfs_remove_recursive(dev->debugfs_dir);
}

Custom File Operations

For complex debug output:

static int stats_show(struct seq_file *s, void *unused)
{
    struct my_dev *dev = s->private;

    seq_printf(s, "TX packets: %llu\n", dev->tx_packets);
    seq_printf(s, "RX packets: %llu\n", dev->rx_packets);
    seq_printf(s, "Errors: %u\n", dev->errors);

    return 0;
}
DEFINE_SHOW_ATTRIBUTE(stats);

/* In probe */
debugfs_create_file("stats", 0444, dev->debugfs_dir, dev, &stats_fops);

Debugfs Helpers

Function	Creates
debugfs_create_u8	8-bit unsigned
debugfs_create_u32	32-bit unsigned
debugfs_create_u64	64-bit unsigned
debugfs_create_bool	Boolean (Y/N)
debugfs_create_x32	Hex 32-bit
debugfs_create_file	Custom operations
debugfs_create_blob	Binary data

Using debugfs

# Mount (usually automatic)
mount -t debugfs none /sys/kernel/debug

# Read value
cat /sys/kernel/debug/my_driver/counter

# Write value
echo 100 > /sys/kernel/debug/my_driver/counter

# View stats
cat /sys/kernel/debug/my_driver/stats

debugfs may not be mounted in production. Don’t rely on it for functionality - only debugging.

Summary

• Use for debug info, register dumps, statistics
• Not ABI stable - can change without warning
• Use debugfs_create_* helpers for simple types
• Use DEFINE_SHOW_ATTRIBUTE for complex output

Further Reading

• debugfs Documentation