Re: [alsa-devel] [PATCH 1/3] ALSA: pcm: implement the anonymous dup (inode file descriptor)

On Tue, 29 Jan 2019 18:59:07 +0100, Jaroslav Kysela wrote:

This patch implements new SNDRV_PCM_IOCTL_ANONYMOUS_DUP ioctl which returns the new duplicated anonymous inode file descriptor (anon_inode:snd-pcm) which can be passed to the restricted clients.

This patch is meant to be the alternative for the dma-buf interface. Both implementation have some pros and cons:

anon_inode:dmabuf

• a bit standard export API for the DMA buffers
• fencing for the concurrent access [1]
• driver/kernel interface for the DMA buffer [1]
• multiple attach/detach scheme [1]

[1] the real usage for the sound PCM is unknown at the moment for this feature

anon_inode:snd-pcm

• simple (no problem with ref-counting, non-standard mmap implementation etc.)
• allow to use more sound interfaces for the file descriptor like status ioctls
• more fine grained security policies (another anon_inode name unshared with other drivers)

Your sign-off seems missing.

@@ -999,15 +1002,19 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream, }

if (file->f_flags & O_APPEND) {

• if (prefer_subdevice < 0) {
  

• 	if (pstr->substream_count > 1)
  

• 		return -EINVAL; /* must be unique */
  

• 	substream = pstr->substream;
  

• if (clone) {
  

• 	substream = clone;
  

  } else {

• 	for (substream = pstr->substream; substream;
  

• 	     substream = substream->next)
  

• 		if (substream->number == prefer_subdevice)
  

• 			break;
  

• 	if (prefer_subdevice < 0) {
  

• 		if (pstr->substream_count > 1)
  

• 			return -EINVAL; /* must be unique */
  

• 		substream = pstr->substream;
  

• 	} else {
  

• 		for (substream = pstr->substream; substream;
  

• 		     substream = substream->next)
  

• 			if (substream->number == prefer_subdevice)
  

• 				break;
  

• 	}
  

  } if (! substream) return -ENODEV;

So the clone case should return via this block, then...

@@ -1018,11 +1025,18 @@ int snd_pcm_attach_substream(struct snd_pcm *pcm, int stream, return 0; }

• for (substream = pstr->substream; substream; substream = substream->next) {

• if (!SUBSTREAM_BUSY(substream) &&
  

•     (prefer_subdevice == -1 ||
  

•      substream->number == prefer_subdevice))
  

• 	break;
  

• if (clone) {

• substream = clone;
  

• if (SUBSTREAM_BUSY(substream))
  

• 	return -EAGAIN;
  

• } else {

• for (substream = pstr->substream; substream;
  

•      substream = substream->next) {
  

• 	if (!SUBSTREAM_BUSY(substream) &&
  

• 	    (prefer_subdevice == -1 ||
  

• 	     substream->number == prefer_subdevice))
  

• 		break;
  

• }
  

... do we need to support cloning without O_APPEND?

thanks,

Takashi