Side effects of open system call

[parinay]

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.
so yes.



HTH


On Fri, Feb 21, 2014 at 9:52 AM, Rahul Bedarkar <rpal143 at gmail.com> wrote:

> On Thu, Feb 20, 2014 at 9:06 PM,  <Valdis.Kletnieks at vt.edu> 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'.
> >
>
> Thanks, Does this mean that if I open a device file with O_NONBLOCK flag
> 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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