Re: [PATCH 3/4] ALSA: timer: Introduce virtual userspace-driven timers

Le 26/07/2024 à 09:47, Ivan Orlov a écrit :

Implement two ioctl calls in order to support virtual userspace-driven ALSA timers.

The first ioctl is SNDRV_TIMER_IOCTL_CREATE, which gets the snd_utimer_info struct as a parameter and returns a file descriptor of a virtual timer. It also updates the `id` field of the snd_utimer_info struct, which provides a unique identifier for the timer (basically, the subdevice number which can be used when creating timer instances).

This patch also introduces a tiny id allocator for the userspace-driven timers, which guarantees that we don't have more than 128 of them in the system.

Another ioctl is SNDRV_TIMER_IOCTL_TRIGGER, which allows us to trigger the virtual timer (and calls snd_timer_interrupt for the timer under the hood), causing all of the timer instances binded to this timer to execute their callbacks.

The maximum amount of ticks available for the timer is 1 for the sake of simplification of the userspace API. 'start', 'stop', 'open' and 'close' callbacks for the userspace-driven timers are empty since we don't really do any hardware initialization here.

Suggested-by: Axel Holzinger aholzinger@gmx.de Signed-off-by: Ivan Orlov ivan.orlov0322@gmail.com

---

Hi,

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diff --git a/sound/core/Kconfig b/sound/core/Kconfig index b970a1734647..3cf82641fc67 100644 --- a/sound/core/Kconfig +++ b/sound/core/Kconfig @@ -251,6 +251,17 @@ config SND_JACK_INJECTION_DEBUG Say Y if you are debugging via jack injection interface. If unsure select "N". +config SND_UTIMER

• bool "Enable support for userspace-controlled virtual timers"
• depends on SND_TIMER
• help

•  Say Y to enable the support of userspace-controlled timers. These
  

•  timers are purely virtual, and they are supposed to be triggered
  

•  from userspace. They could be quite useful when synchronizing the
  

•  sound timing with userspace applications (for instance, when sending
  

•  data through snd-aloop).
  

Unneeded extra new line.

• config SND_VMASTER bool

...

+static void snd_utimer_free(struct snd_utimer *utimer) +{

• snd_timer_free(utimer->timer);
• snd_utimer_put_id(utimer);

Missing kfree(utimer->name); ?

• kfree(utimer);

+}

...

+static int snd_utimer_create(struct snd_utimer_info *utimer_info,

• 	     struct snd_utimer **r_utimer)
  

+{

• struct snd_utimer *utimer;
• struct snd_timer *timer;
• struct snd_timer_id tid;
• int utimer_id;
• int err = 0;
• char *timer_name;
• utimer = kzalloc(sizeof(*utimer), GFP_KERNEL);
• if (!utimer)

• return -ENOMEM;
  

• timer_name = kzalloc(SNDRV_UTIMER_NAME_LEN, GFP_KERNEL);

kasprintf(GFP_KERNEL, "snd-utimer%d", utimer_id); ? and SNDRV_UTIMER_NAME_LEN becomes useless too.

In snd_timer_new() it is copied in a char[64] anyway, and if utimer_id is small, we could even save a few bytes of memory.

CJ

• if (!timer_name) {

• kfree(utimer);
  

• return -ENOMEM;
  

• }
• /* We hold the ioctl lock here so we won't get a race condition when allocating id */
• utimer_id = snd_utimer_take_id();
• if (utimer_id < 0) {

• err = utimer_id;
  

• goto err_take_id;
  

• }
• sprintf(timer_name, "snd-utimer%d", utimer_id);
• utimer->name = timer_name;
• utimer->id = utimer_id;

...