linux-kernel - Re: [PATCH 1/3] leds: trigger: legtrig-bpf: Add ledtrig-bpf module

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Date: Fri, 22 Mar 2024 08:24:59 -0700
From: Yonghong Song <yonghong.song@...ux.dev>
To: Daniel Hodges <hodges.daniel.scott@...il.com>, ast@...nel.org,
 pavel@....cz, lee@...nel.org, linux-leds@...r.kernel.org,
 daniel@...earbox.net, bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] leds: trigger: legtrig-bpf: Add ledtrig-bpf module


On 3/22/24 7:08 AM, Daniel Hodges wrote:
> This patch adds a led trigger that interfaces with the bpf subsystem. It
> allows for BPF programs to control LED activity through calling bpf
> kfuncs. This functionality is useful in giving users a physical
> indication that a BPF program has performed an operation such as
> handling a packet or probe point.
>
> Signed-off-by: Daniel Hodges <hodges.daniel.scott@...il.com>
> ---
>   drivers/leds/trigger/Kconfig       | 10 +++++
>   drivers/leds/trigger/Makefile      |  1 +
>   drivers/leds/trigger/ledtrig-bpf.c | 72 ++++++++++++++++++++++++++++++
>   3 files changed, 83 insertions(+)
>   create mode 100644 drivers/leds/trigger/ledtrig-bpf.c
>
> diff --git a/drivers/leds/trigger/Kconfig b/drivers/leds/trigger/Kconfig
> index d11d80176fc0..30b0fd3847be 100644
> --- a/drivers/leds/trigger/Kconfig
> +++ b/drivers/leds/trigger/Kconfig
> @@ -152,4 +152,14 @@ config LEDS_TRIGGER_TTY
>   
>   	  When build as a module this driver will be called ledtrig-tty.
>   
> +config LEDS_TRIGGER_BPF
> +	tristate "LED BPF Trigger"
> +	depends on BPF
> +	depends on BPF_SYSCALL
> +	help
> +	  This allows LEDs to be controlled by the BPF subsystem. This trigger
> +	  must be used with a loaded BPF program in order to control LED state.
> +	  BPF programs can control LED state with kfuncs.
> +	  If unsure, say N.
> +
>   endif # LEDS_TRIGGERS
> diff --git a/drivers/leds/trigger/Makefile b/drivers/leds/trigger/Makefile
> index 25c4db97cdd4..ac47128d406c 100644
> --- a/drivers/leds/trigger/Makefile
> +++ b/drivers/leds/trigger/Makefile
> @@ -16,3 +16,4 @@ obj-$(CONFIG_LEDS_TRIGGER_NETDEV)	+= ledtrig-netdev.o
>   obj-$(CONFIG_LEDS_TRIGGER_PATTERN)	+= ledtrig-pattern.o
>   obj-$(CONFIG_LEDS_TRIGGER_AUDIO)	+= ledtrig-audio.o
>   obj-$(CONFIG_LEDS_TRIGGER_TTY)		+= ledtrig-tty.o
> +obj-$(CONFIG_LEDS_TRIGGER_BPF)		+= ledtrig-bpf.o
> diff --git a/drivers/leds/trigger/ledtrig-bpf.c b/drivers/leds/trigger/ledtrig-bpf.c
> new file mode 100644
> index 000000000000..e3b0b8281b70
> --- /dev/null
> +++ b/drivers/leds/trigger/ledtrig-bpf.c
> @@ -0,0 +1,72 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * LED BPF Trigger
> + *
> + * Author: Daniel Hodges <hodges.daniel.scott@...il.com>
> + */
> +
> +#include <linux/bpf.h>
> +#include <linux/btf.h>
> +#include <linux/btf_ids.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/leds.h>
> +
> +
> +DEFINE_LED_TRIGGER(ledtrig_bpf);
> +
> +__bpf_hook_start()
> +
> +__bpf_kfunc void bpf_ledtrig_blink(unsigned long delay_on, unsigned long delay_off, int invert)
> +{
> +	led_trigger_blink_oneshot(ledtrig_bpf, delay_on, delay_off, invert);
> +}
> +__bpf_hook_end();
> +
> +BTF_SET8_START(ledtrig_bpf_kfunc_ids)
> +BTF_ID_FLAGS(func, bpf_ledtrig_blink)
> +BTF_SET8_END(ledtrig_bpf_kfunc_ids)
> +
> +static const struct btf_kfunc_id_set ledtrig_bpf_kfunc_set = {
> +	.owner = THIS_MODULE,
> +	.set   = &ledtrig_bpf_kfunc_ids,
> +};
> +
> +static int init_bpf(void)
> +{
> +	int ret;
> +
> +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC,
> +			&ledtrig_bpf_kfunc_set);

If you add the kfunc to BPF_PROG_TYPE_UNSPEC, then
you do not need to add to the following prog types
since the kernel will search BPF_PROG_TYPE_UNSPEC
for all prog types.

But if the kfunc only intends to be used for the following
program types, I suggest removing the above BPF_PROG_TYPE_UNSPEC
registration.

> +	ret = register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
> +			&ledtrig_bpf_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL,
> +			&ledtrig_bpf_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SK_SKB,
> +			&ledtrig_bpf_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS,
> +			&ledtrig_bpf_kfunc_set);
> +	ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_ACT,
> +			&ledtrig_bpf_kfunc_set);
> +	return ret;
> +}
> +
> +static int ledtrig_bpf_init(void)
> +{
> +	led_trigger_register_simple("bpf", &ledtrig_bpf);
> +
> +	return init_bpf();
> +}
> +
> +static void __exit ledtrig_bpf_exit(void)
> +{
> +	led_trigger_unregister_simple(ledtrig_bpf);
> +}
> +
> +module_init(ledtrig_bpf_init);
> +module_exit(ledtrig_bpf_exit);
> +
> +MODULE_AUTHOR("Daniel Hodges <hodges.daniel.scott@...il.com>");
> +MODULE_DESCRIPTION("BPF LED trigger");
> +MODULE_LICENSE("GPL v2");