Messages in this thread | | | Date | Thu, 3 Apr 2008 21:34:09 +0300 (EEST) | From | Kai Makisara <> | Subject | Re: Slow tape drive timeout |
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On Wed, 2 Apr 2008, Robert Hancock wrote:
> Kai Makisara wrote: > > On Tue, 1 Apr 2008, Carlo Nyto wrote: > > > > > I am experiencing a two minute timeout open()ing a tape device when > > > there is no tape in the drive. > > > > > > open() with O_NONBLOCK succeeds immediately, however. > > > > > This is how open() is supposed to work according to standards (e.g., SUS) if > > O_NONBLOCK is supported. (Well, actually open() should wait indefinitely but > > the non-linux systems I tested had a timeout.) The linux st driver was > > changed to comply with standards at 2.5.3. I.e., the 2.4 kernels did return > > immediately but the 2.6 kernels have always waited. > > ... > Why is accessing the tape drive with no tape in it causing a timeout in the > first place? I should think that would fail immediately with some "medium not > present" error from the drive. Unless the drive has no mechanism to detect it, > but that seems really retarded.. > It does not seem retarded to me. If a program wants to just wait until the tape drive becomes ready (e.g., loads the tape), it can use the blocking open. This is simple. If a program wants to test the status, it uses non-blocking open. The behavior mandated by the standards provides alternatives. If O_NONBLOCK is not supported, the user program must implement the waiting logic if the program just wants to wait until the drive is ready before starting i/o.
-- Kai
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