kernel thread and blocking calls

Please help me in understanding blocking and non-blocking calls.
I have the following doubts regarding kernel threads and blocking/non-blocking calls.

My understanding regarding blocking and non-blocking calls is as follows:

A blocking call is one which does not return from that call till the call is completely run. On the other hand, a non-blocking is one which returns immediately if it needs to block for some resource.
Is this understanding correct? Please correct me if i am wrong.


Is there any limitation that a kernel thread should call only blocking-calls in its execution. If yes, what will be the issue if a non-blocking call is called from a kernel thread.

my knowledge is a bit lacking but i will try.
blocking functions is when the calling processes execution is blocked untill the kernel call is completed.
(unless the process recievs a signal)
where the kernel API for a function is non blocking or blocking is the same as asking if the kernel function is implemented using an an asynchronous model or a syncronous model
i think if at all possible the kernel should have everything it can execute asynchronously and certainly a lot of things can be done that way
it is even possible for the kernel internally to be doing a little spinning while the API appears to the user space program to be non blocking or asynchronous.

for instance read() may be important to execute syncronously because you figure the user space program wants to process the read information but write() you can execute asynchronously for better performance to a certain extent as long as you don't think critical data will be lost or whatever other concerns are.