[v2,0/3] leds: trigger: legtrig-bpf: Add ledtrig-bpf trigger

This patch set adds a led trigger that interfaces with the bpf
subsystem. It allows for BPF programs to control LED activity using 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.

V1: https://lore.kernel.org/bpf/cover.1711113657.git.hodges.daniel.scott@gmail.com/
Changes in V2:
- Change kfunc to trigger based on LED name.
- Fix kfunc registration of BPF_PROG_TYPE_UNSPEC.
- Use new kfunc helpers off bpf-next branch.

Daniel Hodges (3):
  leds: trigger: legtrig-bpf: Add ledtrig-bpf trigger
  selftests/bpf: Add selftests for bpf led programs
  leds: trigger: Add documentation for ledtrig-bpf

 Documentation/leds/index.rst                  |  1 +
 Documentation/leds/ledtrig-bpf.rst            | 13 ++++
 drivers/leds/trigger/Kconfig                  | 10 +++
 drivers/leds/trigger/Makefile                 |  1 +
 drivers/leds/trigger/ledtrig-bpf.c            | 73 +++++++++++++++++++
 tools/testing/selftests/bpf/config            |  1 +
 .../testing/selftests/bpf/progs/ledtrig_bpf.c | 32 ++++++++
 7 files changed, 131 insertions(+)
 create mode 100644 Documentation/leds/ledtrig-bpf.rst
 create mode 100644 drivers/leds/trigger/ledtrig-bpf.c
 create mode 100644 tools/testing/selftests/bpf/progs/ledtrig_bpf.c

On Mon, 25 Mar 2024, 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@gmail.com>
> ---
>  drivers/leds/trigger/Kconfig       | 10 ++++
>  drivers/leds/trigger/Makefile      |  1 +
>  drivers/leds/trigger/ledtrig-bpf.c | 73 ++++++++++++++++++++++++++++++
>  3 files changed, 84 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..99cabf816da4
> --- /dev/null
> +++ b/drivers/leds/trigger/ledtrig-bpf.c
> @@ -0,0 +1,73 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * LED BPF Trigger
> + *
> + * Author: Daniel Hodges <hodges.daniel.scott@gmail.com>

Any copyright?

> + */
> +
> +#include <linux/bpf.h>
> +#include <linux/btf.h>
> +#include <linux/btf_ids.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/leds.h>
> +#include <linux/module.h>
> +#include <linux/rcupdate.h>
> +
> +
> +DEFINE_LED_TRIGGER(ledtrig_bpf);
> +
> +__bpf_kfunc_start_defs();

__bpf_hook_start()?

> +__bpf_kfunc void bpf_ledtrig_blink(const char *led_name__str, unsigned long
> +		delay_on, unsigned long delay_off, int invert)

Nit: Try to keep the variable types and names together please.

I.e. break before the 'unsigned' or after 'delay_on'.

> +{
> +	struct led_classdev *led_cdev;
> +
> +	rcu_read_lock();
> +	list_for_each_entry_rcu(led_cdev, &ledtrig_bpf->led_cdevs, trig_list) {
> +		if (strcmp(led_name__str, led_cdev->name) == 0) {
> +			led_blink_set_oneshot(led_cdev, &delay_on, &delay_off,
> +					invert);

Use 100-chars to avoid the break.

> +			break;
> +		}
> +	}
> +	rcu_read_unlock();
> +}
> +__bpf_kfunc_end_defs();

_bpf_hook_end()?

> +BTF_KFUNCS_START(ledtrig_bpf_kfunc_ids)
> +BTF_ID_FLAGS(func, bpf_ledtrig_blink, KF_TRUSTED_ARGS)
> +BTF_KFUNCS_END(ledtrig_bpf_kfunc_ids)

Why not a single macro to output the full struct?

Or better yet, be less opaque and not use a macro at all?

> +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);
> +	return ret;

return register_btf_kfunc_id_set()?

Or again, better yet, put the single function call directly into
ledtrig_bpf_init()?  Creating a whole function just for a single
invocation seems superfluous.

> +}
> +
> +static int __init 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@gmail.com>");
> +MODULE_DESCRIPTION("BPF LED trigger");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.43.2
>

On Mon, 25 Mar 2024, Daniel Hodges wrote:

> Update the documentation for led triggers to include the BPF LED

LED throughout please.

Same in the previous commit please.

> trigger.
> 
> Signed-off-by: Daniel Hodges <hodges.daniel.scott@gmail.com>
> ---
>  Documentation/leds/index.rst       |  1 +
>  Documentation/leds/ledtrig-bpf.rst | 13 +++++++++++++
>  2 files changed, 14 insertions(+)
>  create mode 100644 Documentation/leds/ledtrig-bpf.rst
> 
> diff --git a/Documentation/leds/index.rst b/Documentation/leds/index.rst
> index 3ade16c18328..2af52a19d6bb 100644
> --- a/Documentation/leds/index.rst
> +++ b/Documentation/leds/index.rst
> @@ -10,6 +10,7 @@ LEDs
>     leds-class
>     leds-class-flash
>     leds-class-multicolor
> +   ledtrig-bpf
>     ledtrig-oneshot
>     ledtrig-transient
>     ledtrig-usbport
> diff --git a/Documentation/leds/ledtrig-bpf.rst b/Documentation/leds/ledtrig-bpf.rst
> new file mode 100644
> index 000000000000..391a305f69d1
> --- /dev/null
> +++ b/Documentation/leds/ledtrig-bpf.rst
> @@ -0,0 +1,13 @@
> +====================
> +BPF LED Trigger
> +====================
> +
> +This LED trigger is useful for triggering LEDs from the BPF subsystem.  This
> +trigger is designed to be used in combination with a BPF program that interacts
> +with the trigger via a kfunc.  The exported kfuncs will have BTF names that
> +start with "bpf_ledtrig_".
> +
> +The trigger can be activated from user space on led class devices as shown
> +below::
> +
> +  echo bpf > trigger
> -- 
> 2.43.2
>