Date: Mon, 9 Oct 2000 14:20:18 -0700 (PDT)
From: Westley Weimer <weimer@EECS.Berkeley.EDU>
Subject: Linux device drivers: O_NONBLOCK in fops->open ...
Message-ID: <Pine.SOL.4.10.10010091413080.3747-100000@york.CS.Berkeley.EDU>
I have a question about O_NONBLOCK and the open() method that Rubini is a
little fuzzy on. Here's a quote from page 110:
As you may imagine from its name, O_NONBLOCK is meaningful also in the
open method. This happens when the call can actually block for a long
time; for example, when opening a FIFO that has no writers yet), or
accessing a disk file with a pending lock. Usually, opening a device
either succeeds or fails, without the need to wait for external events.
Sometimes, however, opening the device requires a long initialization,
and you may choose to check O_NONBLOCK, returning immediately with
-EAGAIN (try it again) if the flag is set, after spawning device
initialization. You might also decide to implement a blocking open ...
Only the read, write and open file operations are affected by the
nonblocking flag.
Here's the question: Is the driver writer allowed to put a process to sleep
(= block) in the open method if the O_NONBLOCK flag is set? [
drivers/char/qpmouse.c in 2.2.15 is an example of a simple driver that does
so. ] "You may choose" sounds quite weak. Does anyone have more information
on this?
- Wes
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