O_NONBLOCK
If possible, the file will be opened in nonblocking mode. Neither the open() call,
nor any other operation will cause the process to block (sleep) on the I/O. This
behaviour may be defined only for FIFOs.
Sometimes, programmers do not want a call to read() to block when there is no data
available. Instead, they prefer that the call return immediately, indicating that no data
is available. This is called nonblocking I/O; it allows applications to perform I/O, potentially
on multiple files, without ever blocking, and thus missing data available in
another file.
Consequently, an additional errno value is worth checking: EAGAIN.
- from - Linux system programming second edition R Love.
If possible, the file will be opened in nonblocking mode. Neither the open() call,
nor any other operation will cause the process to block (sleep) on the I/O. This
behaviour may be defined only for FIFOs.
Sometimes, programmers do not want a call to read() to block when there is no data
available. Instead, they prefer that the call return immediately, indicating that no data
is available. This is called nonblocking I/O; it allows applications to perform I/O, potentially
on multiple files, without ever blocking, and thus missing data available in
another file.
Consequently, an additional errno value is worth checking: EAGAIN.
- from - Linux system programming second edition R Love.
so yes.
On Fri, Feb 21, 2014 at 9:52 AM, Rahul Bedarkar <rpal143@xxxxxxxxx> wrote:
Thanks, Does this mean that if I open a device file with O_NONBLOCK flagOn Thu, Feb 20, 2014 at 9:06 PM, <Valdis.Kletnieks@xxxxxx> wrote:
> On Thu, 20 Feb 2014 20:36:44 +0530, Rahul Bedarkar said:
>
>> "Often the open(2) call has unwanted side effects, that can be avoided
>> under Linux by giving it the O_NONBLOCK flag."
>>
>> I have seen open man page but can't find what are side effects of open.
>
> Well, for starters, the open() call can block while trying to open a hardware
> device that isnt ready, thus hanging the entire process. For added joy,
> remember that signals are delivered when a process inside a syscall finally
> returns to userspace - which means that your hung process may be unkillable
> even by 'kill -9'.
>
and if device is not ready by that time open system call will return
immediately and fail?
_______________________________________________
> Most people would call that an unwanted side effect. :)
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