O_NONBLOCK for devices with removable media

[victor cruceru]

Hi Marc,
Thanks for the info. Here it is one my situation. I have a CF reader (fully 
detected by the USB subsystem) with two slots
(one with a media and one without any media). An open with O_NONBLOCK on the 
empty slot (/dev/da1) is blocking me.
Is this OK? 
Thanks,
Victor 


On 8/1/05, Marc Olzheim <marcolz at stack.nl> wrote:
> 
> On Mon, Aug 01, 2005 at 02:42:21PM +0300, victor cruceru wrote:
> > Hi all,
> > I'm just wondering if it's OK for an open syscall on such a device (i.e.
> > /dev/acd0 or /dev/da1 with a CF reader attached) to block till the media 
> is
> > ready or a timeout occurs.
> 
> I'd say that depends completely on whether you supply O_NONBLOCK or not,
> so yes.
> 
> Quoted from a sound driver discussion at:
> http://sourceforge.net/mailarchive/message.php?msg_id=10011826
> 
> 
> On block devices, O_NONBLOCK also is a way to say "don't try to do any
> device discovery", ie you can do a O_NONBLOCK open on a removable disk
> that doesn"t even have any media in it. Again, this has _nothing_ to do
> with whether the device is "busy" or not.
> 
> ...
> 
> Short summary:
> 
> - O_NONBLOCK should generally be seen as just setting the O_NONBLOCK flag
> "early" (ie it"s conceptually equivalent to doing a "F_SETFL" fcntl
> before the open. It _may_ affect the open itself, but when it does, it
> is generally considered to mean that you can open something that isn't
> even _reachable_.
> 
> - POSIX doesn't say anything much about its behaviour, except for named
> pipes, where it says the total reverse of what ALSA does. But that
> doesn't actually mean anything, because even that is very much defined
> as a special case by POSIX.
> 
> Marc
> 
> 
>