Fixing audio/oss to use callout instead of timeouts

[John Baldwin]

On 1/2/20 3:47 PM, Chris Rees wrote:
> Hi Hackers (and perhaps John, as the author of r355732, sorry for the duplicate),
> 
> I've attempted to use the callout functions instead of the now removed timeout functions for audio/oss, and I *think* that the code already stores and retrieves the list of handlers, so it should be a simple swap out.
> 
> I've made this modification and run the module with mpg123 for a while and it hasn't killed my laptop, but I'd just like to check that I have the principle correct and haven't missed anything obvious.
> 
> Please would you let me know if there is anything else I should have done?
> 
> https://www.bayofrum.net/cgi-bin/fossil/oss/vinfo/ad269d7cbc02bf38?diff=2
> 
> (This is the change I've made to kernel/OS/FreeBSD/os_freebsd.c in oss)
> 
> https://www.bayofrum.net/cgi-bin/fossil/oss/vinfo/ad269d7cbc02bf38?diff=2&dc=9999

A few suggestions:

1) You should do the callout_init() during a SYSINIT or MOD_LOAD event to initialize
   all the timers at once instead of doing it in oss_timeout().

2) You should then add a SYSUNINIT or MOD_UNLOAD that uses callout_drain().

3) You should add a mutex to protect the tmouts array and timeout_random, etc.
   and use callout_init_mtx with that lock, but probably use CALLOUT_RETURNUNLOCKED
   and drop the mutex right before calling the function (you can store the function
   pointer and void * argument in local variables before dropping the lock to
   be safe.

4) If possible, you should really alter the oss API so that drivers don't use
   a timeout()-like interface, but instead use a callout directly (or an interface
   that wraps callout).  This would let drivers take advantage of callout_init_mtx
   with their own locks, etc.

Does audio/oss contain all the code that makes use of oss_timeout?

-- 
John Baldwin