On Mon, Aug 01, 2005 at 04:33:23PM +0300, victor cruceru wrote: > 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.
It should not block for a long time since the device should directly reply with either ready or no media. > Is this OK? No, but it is a broken device if you don't get back in a resonable time. I don't think that O_NONBLOCK is ment to never block for a short time. In case of disks you have to ask the device for ready state, if you don't allow blocking you can't do that and therefor never successfull open a disk. The intention should read more in the sense of, don't wait for a disk to spin up, but even this is problematic to implement correct with many devices. > On 8/1/05, Marc Olzheim <[EMAIL PROTECTED]> 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. -- B.Walter BWCT http://www.bwct.de [EMAIL PROTECTED] [EMAIL PROTECTED] _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
