how is kernel notifying userspace when data arrives on a socket/fd

jork · 06-25-2010, 03:14 AM

Hi All,

I was trying to find how the kernel notifies Userspace when data arrives on a socket or a socket/fd becomes writable. I know from userspace we call select() if its non-blocking and it wakes up. But my question is exactly that, how select finds this.
I've gone through a little bit of kernel TCP code. Where i'm seeing SIGIOs are being sent to the process. Is this the sole way kernel notifies uspace? What does the wake_up_interruptible() function do?

Thanks,
Joshith

kumar.manoj412 · 06-25-2010, 03:27 AM

Quote:

Originally Posted by jork

Hi All,

I was trying to find how the kernel notifies Userspace when data arrives on a socket or a socket/fd becomes writable. I know from userspace we call select() if its non-blocking and it wakes up. But my question is exactly that, how select finds this.
I've gone through a little bit of kernel TCP code. Where i'm seeing SIGIOs are being sent to the process. Is this the sole way kernel notifies uspace? What does the wake_up_interruptible() function do?

Thanks,
Joshith

Hello,

You also can try by asynchronous signals. In user space you will run a process which will response the kernel signals. Try LDD3 examples.

jork · 06-25-2010, 03:57 AM

Kumar,

Thanks for the reply. But can you elaborate a little bit more on this.
I understand a SIGIO ie. an async signal is sent by the kernel. But I was wondering is there any other means also by which kernel notify the uspace program.

sk_wake_async(sk,0,POLL_OUT);
sk_wake_async(sk,1,POLL_IN);
sk_wake_async(sk,0,POLL_ERR); are in the send sending SIGIO. what does wake_up_interruptible() do here?

thanks,
jork