Strange err=25 result.

Strange err=25 result.

[James Courtier-Dutton]

Some debug output from calling snd_pcm_wait() when a USB device is 
unplugged.

(pcm_hw.c from /alsa-lib/src/pcm/pcm_hw.c)
file=pcm_hw.c:406 function=snd_pcm_hw_status err=25
pcm_hw.c: snd_pcm_hw_status() SNDRV_PCM_IOCTL_STATUS failed.

According to errno.h,
#define ENOTTY          25      /* Not a typewriter */

I would think that the following would be a better err result.
#define ENODEV          19      /* No such device */
or even
#define EPIPE           32      /* Broken pipe */

I have looked through alsa-lib and alsa-kernel and cannot find any place 
in the code that sets errno to 25!

Can anybody help?

My aim is to let the application detect when a usb audio device is 
unplugged, so that the application can release all alsa resources.
The application will then poll the alsa-lib trying to open the device 
again, and continually get errors until the audio usb device is plugged 
in again. For my application to achieve this, I would need a specific 
errno for the "usb device unplugged" that will not get confused with 
over/underruns or other errors that might not be "usb unplugged" related.

Cheers
James


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Re: Strange err=25 result.

[Jaroslav Kysela]

On Wed, 14 Jan 2004, James Courtier-Dutton wrote:

> Some debug output from calling snd_pcm_wait() when a USB device is 
> unplugged.
> 
> (pcm_hw.c from /alsa-lib/src/pcm/pcm_hw.c)
> file=pcm_hw.c:406 function=snd_pcm_hw_status err=25
> pcm_hw.c: snd_pcm_hw_status() SNDRV_PCM_IOCTL_STATUS failed.
> 
> According to errno.h,
> #define ENOTTY          25      /* Not a typewriter */
> 
> I would think that the following would be a better err result.
> #define ENODEV          19      /* No such device */
> or even
> #define EPIPE           32      /* Broken pipe */
> 
> I have looked through alsa-lib and alsa-kernel and cannot find any place 
> in the code that sets errno to 25!
> 
> Can anybody help?

Consult the toplevel filesystem routines. In case when the device is 
disconnected, all i/o (filesystem operation) calls are redirected to empty 
structure, so the Linux kernel filesystem code probably returns ENOTTY 
errors when no ioctl/read/write callbacks are associated to the device.

						Jaroslav

-----
Jaroslav Kysela <perex@suse.cz>
Linux Kernel Sound Maintainer
ALSA Project, SuSE Labs


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Re: Strange err=25 result.

[James Courtier-Dutton]

Jaroslav Kysela wrote:
> On Wed, 14 Jan 2004, James Courtier-Dutton wrote:
> 
> 
>>Some debug output from calling snd_pcm_wait() when a USB device is 
>>unplugged.
>>
>>(pcm_hw.c from /alsa-lib/src/pcm/pcm_hw.c)
>>file=pcm_hw.c:406 function=snd_pcm_hw_status err=25
>>pcm_hw.c: snd_pcm_hw_status() SNDRV_PCM_IOCTL_STATUS failed.
>>
>>According to errno.h,
>>#define ENOTTY          25      /* Not a typewriter */
>>
>>I would think that the following would be a better err result.
>>#define ENODEV          19      /* No such device */
>>or even
>>#define EPIPE           32      /* Broken pipe */
>>
>>I have looked through alsa-lib and alsa-kernel and cannot find any place 
>>in the code that sets errno to 25!
>>
>>Can anybody help?
> 
> 
> Consult the toplevel filesystem routines. In case when the device is 
> disconnected, all i/o (filesystem operation) calls are redirected to empty 
> structure, so the Linux kernel filesystem code probably returns ENOTTY 
> errors when no ioctl/read/write callbacks are associated to the device.
> 
> 						Jaroslav

Thank you, that makes sense. :-)

Also, what should
snd_pcm_wait()
and
snd_pcm_state()
return if the USB device is unplugged.

At the moment, snd_pcm_wait() just hangs around until the timeout and 
returns errno -5
and snd_pcm_state() still returns state=3 which is SND_PCM_STATE_RUNNING

I would hardly say the the card is still in "RUNNING" state if you 
physically remove the card from the system!

I would prefer snd_pcm_wait() to imeadiately exit with an errno, and 
snd_pcm_state() to return a new state of "SND_PCM_STATE_DISCONNECTED" or 
similar.

Can I do what I want with snd_pcm_wait or not?

Cheers
James


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