Re: TODO list

[James Courtier-Dutton <James@superbug.co.uk>]

Takashi Iwai wrote:
> At Fri, 26 May 2006 12:29:11 +0100,
> James Courtier-Dutton wrote:
>   
>> Takashi Iwai wrote:
>>     
>>>> 7) Provide better OSS emulation support. E.g. redirect all access to 
>>>> /dev/dsp into user space so it can use all the features of alsa-lib 
>>>> without needing aoss. (aoss does not work if the application uses 
>>>> dynamically linked audio driver plugins.
>>>>     
>>>>         
>>> A dummy kernel driver just to translate syscalls to communication with
>>> a user daemon is the only possible workaround, IMO.  This idea was
>>> denied once quite ago, but I don't see any other good way right now.
>>>   
>>>       
>> That is my thought as well. When I looked into the idea some time ago, I 
>> concluded that is would be a rather large project, so I did not proceed 
>> as I have other more important (for me) ALSA features.
>> Can a user space daemon create /dev files, so that the application calls 
>> never actually reach kernel space?
>>     
>
> No, only the kernel driver can handle certain syscalls like ioctl and
> mmap properly.  So, it must be a kernel driver that communicated with
> OSS apps (unless using LD_PRELOAD hack).
>
> The driver interprets each syscall to a certain protocol communicated
> with a dedicated daemon, and the daemon interprets it again to the
> real ALSA access.
>
>   
>> If we can create such a pipe, that can forward 
>> open/close/read/write/ioctl, that should be enough. We then have to 
>> think about shared memory to look like DMA space to the application 
>> using us.
>>     
>
> mmap would be still tricky, maybe a kind of emulation via read/write.
>
>
> Takashi
>   

For mmap, all that happens is that the application asks for a mmap 
address from the kernel.
If we could get the kernel to manipulate shared memory, so that the mmap 
address given to the application is shared with the daemon, surely that 
would work.
Unfortunately, this might require some kernel memory manager modifications.
Shall I ask about this on the kernel mm list?

James