On Wed, Oct 17, 2001 at 04:43:55AM -0400, Roland McGrath wrote: > > There are some details about the implementation which are not ideal, but ok: > > Once a task gets a bitmap, it is never destroyed, even if no I/O ports are > > enabled (all bits set). The bitmap is destroyed only with the task. > > All bits clear you mean.
Actually, I mean all bits set, as no permission is denoted by a 1 in the bitmap (that's why the barrier is 0xff, I guess). I think keeping the bitmap around at the risk that it is not used anymore is better than the risk that io_permissions are often switched and you end up allocatin and freeing often. For both cases it is true that they probably never will happen. > > A task requesting some I/O permission will get a full blown 8192 bytes large > > bitmap, which is copied in the processor TSS at every switch to the task. > > (Linux by default only uses a half bitmap, and provides a full one at > > request by calling a special function -- not ideal either, interface-wise). > > I'm not sure what Linux you are looking at (I'm reading 2.4.3 sources). > What I see is that is copies only 1024 bits (32 bytes) for ioperm. To > access the io ports above 1023 you have to call iopl to just run at IOPL0. In German you would say that I have tomatoes on my eyes. ;) > > * I don't know if and where I need to lock the task or the contained bitmap. > > Mach is nonpreemptive. You only need to do SMP locking (simple_lock). Mmh. What about i386_io_perm_modify vs. task_terminate on SMP? I don't want to scribble in deallocated pages. Also, what about i386_io_perm_modify vs another cpu switching to another thread in the same task? The bad kinds of interactions I am worried about is not so much the io_perm interface with itself, but with task_terminate on the one hand and the scheduler on the other hand. Do I use a simple lock in the machine_task and make them all use it? > > * When setting the global descriptor table entry, I use kvtolin for the > > segment address. Roland didn't do this in the multiprocessor code, a bug? > > Or am I wrong in doing the conversion? > > I think that was a bug in code that had never been run, and your fix is right. It was only used for SMP. BTW, I did not fix it for your code in my patch, but will d os. All other suggestions will also be picked up by me. Thanks a lot for the input, Marcus -- `Rhubarb is no Egyptian god.' Debian http://www.debian.org [EMAIL PROTECTED] Marcus Brinkmann GNU http://www.gnu.org [EMAIL PROTECTED] [EMAIL PROTECTED] http://www.marcus-brinkmann.de _______________________________________________ Bug-hurd mailing list [EMAIL PROTECTED] http://mail.gnu.org/mailman/listinfo/bug-hurd
