[Debburn-devel] Re: broken device locking, sg vs. sg_io on block devices

[Eduard Bloch]

#include <hallo.h>

First, we (me and Thomas Schmidt) are working on a draft for a mandatory
locking scheme which will take care of the most racy situations even
without having a proper in-kernel solution. But you need to exlain some
things, otherwise we cannot rely on your words.

> (open has side effects relocking doesnt)

What exactly does that mean in our scope?

Can we do following without having side effects:

open("/dev/sr0",O_EXCL|O_RDWR); /* no matter what it returns */
fcntl(..., F_SETLK); /* no matter what it returns */
ioctl(f, SCSI_IOCTL_GET_IDLUN, &x);
ioctl(f, SCSI_IOCTL_GET_BUS_NUMBER, &jo);

Can you guarantee us that bit? 

Or shall we really implement ugly workarounds to avoid every open call?
Note that "just do like UUCP guys" is not as easy or reliable as people
may pretend.

Eduard.

-- 
Naja, Garbage Collector eben. Holt den Müll sogar vom Himmel.
       (Heise Trollforum über Java in der Flugzeugsteuerung)