RE: kernel to user-space communication

[Woodruff, Robert J]

There are a couple of techniques one can use.
First, you can set up a piece of memory that is shared
between the kernel and the user process and when the 
interrupt occurs, set a flag in memory. The user process
can poll the memory to see if an interrupt happened.

Coarse, you might not want to waist CPU polling all day,
so you could use signals (like SIGUSR1) to block, and have the 
kernel send the signal when the interrupt occurs. Only problem
with signals is that they are not stackable.

Another technique is to implement the concept of a wait object,
you write a simple driver that manages these. The user process
does an ioctl to the wait object driver when it wants to wait for 
an interrupt. The ioctl sleeps if the interrupt has not occurred.
The kernel then calls wakeup when the interrupt 
happens and the ioctl completes. 
We implemented a mechanism like this for InfiniBand,
which allows user level I/O to the hardware and we needed a way to
signal I/O completions (interrupts) to the user process. 
If you are interested
in an example, take a look at the early reference InfiniBand code
at http://sourceforge.net/projects/infiniband.

-----Original Message-----
From: daniel sheltraw [mailto:[e-mail]]
Sent: Monday, August 12, 2002 8:40 AM
To: [e-mail]
Subject: kernel to user-space communication

Hello Kernel

Is there a way to comminicate to a user-space program that an
interrupt has occurred in a kernel module?

Thanks,
Daniel Sheltraw

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