On Mon, Nov 03, 2014 at 12:10:49PM +0000, One Thousand Gnomes wrote: > On Sun, 2 Nov 2014 09:33:01 -0800 > Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote: > > > On the vast majority of modern systems, no processes will use the > > userspsace IO syscalls, iopl and ioperm. Add a new config option, > > CONFIG_X86_IOPORT, to support configuring them out of the kernel > > entirely. Most current systems do not run programs using these > > syscalls, so X86_IOPORT does not depend on EXPERT, though it does still > > default to y. > > This isn't unreasonable but there are drivers with userspace helpers that > use iopl/ioperm type functionality where you should be doing a SELECT of > X86_IOPORT. The one that comes to mind is the uvesa driver. From a quick > scan it may these days be the only mainstream one that needs the select > adding. Should kernel drivers really express dependencies that only their (current instances of) corresponding userspace components need? Something seems wrong about that. > Some X servers for legacy cards still use io port access. Sure, X servers using UMS rather than KMS seem like a common reason to need this. > There are also > a couple of other highly non-obvious userspace users that hang on for > some systems - eg some older servers DMI and error records can only by > read via a real mode BIOS call so management tools have no choice but to > go the lrmi/io path. As with any userspace interface, some callers may potentially still exist. And this still has "default y", too, to avoid user surprises. > Still makes sense IMHO. > > From a code perspective however you could define IO_BITMAP_LONGS to 0, > add an IO_BITMAP_SIZE (defined as LONGS + 1 or 0) and as far as I can see > gcc would then optimise out a lot of the code you are ifdeffing IO_BITMAP_LONGS already gets defined to (0/sizeof(long)). And as far as I can tell, that would only work for init_tss_io, not anything else. Even then, that would only work with a zero-size array left around in tss_struct, which doesn't seem appropriate. The remaining ifdefs wrap code that GCC could not constant-fold away, and making that code constant-foldable seems significantly more invasive than the ifdefs. - Josh Triplett _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
