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Commit becf9e5d authored by Takashi Sakamoto's avatar Takashi Sakamoto Committed by Takashi Iwai
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ALSA: control: code refactoring for ELEM_READ/ELEM_WRITE operations 



ALSA control core handles ELEM_READ/ELEM_WRITE requests within lock
acquisition of a counting semaphore. The lock is acquired in helper
functions in the end of call path before calling implementations of each
driver.

ioctl(2) with SNDRV_CTL_ELEM_READ
...
->snd_ctl_ioctl()
  ->snd_ctl_elem_read_user()
    ->snd_ctl_elem_read()
      ->down_read(controls_rwsem)
      ->snd_ctl_find_id()
      ->struct snd_kcontrol.get()
      ->up_read(controls_rwsem)

ioctl(2) with SNDRV_CTL_ELEM_WRITE
...
->snd_ctl_ioctl()
  ->snd_ctl_elem_write_user()
    ->snd_ctl_elem_write()
      ->down_read(controls_rwsem)
      ->snd_ctl_find_id()
      ->struct snd_kcontrol.put()
      ->up_read(controls_rwsem)

This commit moves the lock acquisition to middle of the call graph to
simplify the helper functions. As a result:

ioctl(2) with SNDRV_CTL_ELEM_READ
...
->snd_ctl_ioctl()
  ->snd_ctl_elem_read_user()
    ->down_read(controls_rwsem)
    ->snd_ctl_elem_read()
      ->snd_ctl_find_id()
      ->struct snd_kcontrol.get()
    ->up_read(controls_rwsem)

ioctl(2) with SNDRV_CTL_ELEM_WRITE
...
->snd_ctl_ioctl()
  ->snd_ctl_elem_write_user()
    ->down_read(controls_rwsem)
    ->snd_ctl_elem_write()
      ->snd_ctl_find_id()
      ->struct snd_kcontrol.put()
    ->up_read(controls_rwsem)

Signed-off-by: default avatarTakashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 7b42cfaf

sound/core/control.c

+38 −39
Original line number Diff line number Diff line
@@ -881,24 +881,18 @@ static int snd_ctl_elem_read(struct snd_card *card, 
	struct snd_kcontrol *kctl;

	struct snd_kcontrol_volatile *vd;

	unsigned int index_offset;

	int result;



	down_read(&card->controls_rwsem);

	kctl = snd_ctl_find_id(card, &control->id);

	if (kctl == NULL) {

		result = -ENOENT;

	} else {

	if (kctl == NULL)

		return -ENOENT;



	index_offset = snd_ctl_get_ioff(kctl, &control->id);

	vd = &kctl->vd[index_offset];

		if ((vd->access & SNDRV_CTL_ELEM_ACCESS_READ) &&

		    kctl->get != NULL) {

	if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) && kctl->get == NULL)

		return -EPERM;



	snd_ctl_build_ioff(&control->id, kctl, index_offset);

			result = kctl->get(kctl, control);

		} else

			result = -EPERM;

	}

	up_read(&card->controls_rwsem);

	return result;

	return kctl->get(kctl, control);

}



static int snd_ctl_elem_read_user(struct snd_card *card,
@@ -913,8 +907,11 @@ static int snd_ctl_elem_read_user(struct snd_card *card, 


	snd_power_lock(card);

	result = snd_power_wait(card, SNDRV_CTL_POWER_D0);

	if (result >= 0)

	if (result >= 0) {

		down_read(&card->controls_rwsem);

		result = snd_ctl_elem_read(card, control);

		up_read(&card->controls_rwsem);

	}

	snd_power_unlock(card);

	if (result >= 0)

		if (copy_to_user(_control, control, sizeof(*control)))
@@ -931,29 +928,28 @@ static int snd_ctl_elem_write(struct snd_card *card, struct snd_ctl_file *file, 
	unsigned int index_offset;

	int result;



	down_read(&card->controls_rwsem);

	kctl = snd_ctl_find_id(card, &control->id);

	if (kctl == NULL) {

		result = -ENOENT;

	} else {

	if (kctl == NULL)

		return -ENOENT;



	index_offset = snd_ctl_get_ioff(kctl, &control->id);

	vd = &kctl->vd[index_offset];

		if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_WRITE) ||

		    kctl->put == NULL ||

	if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_WRITE) || kctl->put == NULL ||

	    (file && vd->owner && vd->owner != file)) {

			result = -EPERM;

		} else {

		return -EPERM;

	}



	snd_ctl_build_ioff(&control->id, kctl, index_offset);

	result = kctl->put(kctl, control);

		}

	if (result < 0)

		return result;



	if (result > 0) {

		struct snd_ctl_elem_id id = control->id;

		snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, &id);

			result = 0;

		}

	}

	up_read(&card->controls_rwsem);

	return result;



	return 0;

}



static int snd_ctl_elem_write_user(struct snd_ctl_file *file,
@@ -970,8 +966,11 @@ static int snd_ctl_elem_write_user(struct snd_ctl_file *file, 
	card = file->card;

	snd_power_lock(card);

	result = snd_power_wait(card, SNDRV_CTL_POWER_D0);

	if (result >= 0)

	if (result >= 0) {

		down_read(&card->controls_rwsem);

		result = snd_ctl_elem_write(card, file, control);

		up_read(&card->controls_rwsem);

	}

	snd_power_unlock(card);

	if (result >= 0)

		if (copy_to_user(_control, control, sizeof(*control)))