Re: Synchronization Techniques in 2.2 Kernel

[Brian Strand <bstrand@switchmanagement.com>]

Wayne Cuddy wrote:

>If I understand wait_queues correctly the process has to be sleeping before a
>wake_up call will have any effect (I.E. they are not queued).  Can this be
>worked around with semaphores or some other method?  I am open to ideas here.
>
>Any and all help is appreciated.
>
>Wayne
>
I apologize in advance if this is not quite right, having only done 
"hello world" kernel modules thus far (plus a good deal of kernel source 
browsing).  I think you need to "unfold" the interruptible_sleep_on call 
and do it yourself by adding current to the wait queue before checking 
any cards, setting current->state = TASK_INTERRUPTIBLE, then checking 
all cards and if none has data, calling schedule.  When you get back 
from schedule (i.e. your ISR has received data and done a wake_up) or 
any card has data, remove yourself from the wait queue and set your 
state to runnable.  This hopefully gives you the "atomic check condition 
and sleep if not satisfied" behavior.

Regards,
Brian Strand