(linux kernel) Adding new functions in available_filter_functions

Hardware - Raspberry pi 4 Model B 8GBOS - Raspberry pi OS Buster(10)(2020-05-27-raspios-buster-full-armhf.img)(linux kerenl 4.19.y)

I added rpi_get_interrupt_info() and modified show_interrupts() in proc.c

Full code of rpi_get_interrupt_info() and show_interrupts()

void rpi_get_interrupt_info(struct irqaction *action_p){    unsigned int irq_num = action_p->irq;    void *irq_handler = NULL;    if (action_p->handler) {        irq_handler = (void*)action_p->handler;    }    if (irq_handler) {        trace_printk("[%s] %d: %s, irq_handler: %pS \n",                        current->comm, irq_num, action_p->name, irq_handler);    }}int show_interrupts(struct seq_file *p, void *v){    static int prec;    unsigned long flags, any_count = 0;    int i = *(loff_t *) v, j;    struct irqaction *action;    struct irq_desc *desc;    if (i > ACTUAL_NR_IRQS)        return 0;    if (i == ACTUAL_NR_IRQS)        return arch_show_interrupts(p, prec);    /* print header and calculate the width of the first column */    if (i == 0) {        for (prec = 3, j = 1000; prec < 10 && j <= nr_irqs; ++prec)            j *= 10;        seq_printf(p, "%*s", prec + 8, "");        for_each_online_cpu(j)            seq_printf(p, "CPU%-8d", j);        seq_putc(p, '\n');    }    rcu_read_lock();    desc = irq_to_desc(i);    if (!desc)        goto outsparse;    if (desc->kstat_irqs)        for_each_online_cpu(j)            any_count |= *per_cpu_ptr(desc->kstat_irqs, j);    if ((!desc->action || irq_desc_is_chained(desc)) && !any_count)        goto outsparse;    seq_printf(p, "%*d: ", prec, i);    for_each_online_cpu(j)        seq_printf(p, "%10u ", desc->kstat_irqs ?                    *per_cpu_ptr(desc->kstat_irqs, j) : 0);    raw_spin_lock_irqsave(&desc->lock, flags);    if (desc->irq_data.chip) {        if (desc->irq_data.chip->irq_print_chip)            desc->irq_data.chip->irq_print_chip(&desc->irq_data, p);        else if (desc->irq_data.chip->name)            seq_printf(p, " %8s", desc->irq_data.chip->name);        else            seq_printf(p, " %8s", "-");    } else {        seq_printf(p, " %8s", "None");    }    if (desc->irq_data.domain)        seq_printf(p, " %*d", prec, (int) desc->irq_data.hwirq);    else        seq_printf(p, " %*s", prec, "");#ifdef CONFIG_GENERIC_IRQ_SHOW_LEVEL    seq_printf(p, " %-8s", irqd_is_level_type(&desc->irq_data) ? "Level" : "Edge");#endif    if (desc->name)        seq_printf(p, "-%-8s", desc->name);    action = desc->action;    if (action)        rpi_get_interrupt_info(action);    if (action) {        seq_printf(p, "  %s", action->name);        while ((action = action->next) != NULL)            seq_printf(p, ", %s", action->name);    }    seq_putc(p, '\n');    raw_spin_unlock_irqrestore(&desc->lock, flags);outsparse:    rcu_read_unlock();    return 0;}#endif

Code I changed

void rpi_get_interrupt_info(struct irqaction *action_p){    unsigned int irq_num = action_p->irq;    void *irq_handler = NULL;    if (action_p->handler) {        irq_handler = (void*)action_p->handler;    }    if (irq_handler) {        trace_printk("[%s] %d: %s, irq_handler: %pS \n",                        current->comm, irq_num, action_p->name, irq_handler);    }}....if (action)        rpi_get_interrupt_info(action);

when I try echo rpi_get_interrupt_info > /sys/kernel/debug/tracing/set_ftrace_filter, it says echo: write error: Invalid argument

So I looked /sys/kernel/debug/tracing/available_filter_functions, and there's no rpi_get_interrupt_info

I tried noinline void rpi_get_interrupt_info(struct irqaction *action_p), but it doesn't work.