implementing blocking syscalls in Linux

Question

I would like to understand how implementing blocking I/O syscalls is different from non-blocking? Googling it didn't help much, any links or references would be greatly appreciated.

Thanks.

Answer 1

http://faculty.salina.k-state.edu/tim/ossg/Device/blocking.html

Blocking syscall will put the task (calling thread) to sleep (block it from running on CPU), and syscall will return only after event (or timeout). Non-blocking syscall will not block thread, it just checks in-kernel states and immediately returns.

More detailed description: http://www.makelinux.net/ldd3/chp-6-sect-2

one important issue: how does a driver respond if it cannot immediately satisfy the request? A call to read may come when no data is available, but more is expected in the future. Or a process could attempt to write, but your device is not ready to accept the data, because your output buffer is full. The calling process usually does not care about such issues; the programmer simply expects to call read or write and have the call return after the necessary work has been done. So, in such cases, your driver should (by default) block the process, putting it to sleep until the request can proceed. ....

There are several forms of wait_event kernel functions to block the caller thread, check include/linux/wait.h; thread can be waked up by different ways, for example with wake_up/wake_up_interruptible.