On 05/09/2014 03:38 PM, Josh Triplett wrote: > On Fri, May 09, 2014 at 02:20:45PM -0700, H. Peter Anvin wrote: >> On 05/09/2014 02:12 PM, Arnd Bergmann wrote: >>> >>>> However, if we're going to have these devices I'm wondering if having >>>> /dev/portw and /dev/portl (or something like that) might not make sense, >>>> rather than requiring a system call per transaction. >>> >>> Actually the behavior of /dev/port for >1 byte writes seems questionable >>> already: There are very few devices on which writing to consecutive >>> port numbers makes sense. Normally you just want to write a series >>> of bytes (or 16/32 bit words) into the same port number instead, >>> as the outsb()/outsw()/outsl() functions do. >>> >> >> Indeed. I missed the detail that it increments the port index; it is >> virtually guaranteed to be bogus. > > Exactly. It might make sense to have ioport8/ioport16/ioport32 devices > that accept arbitrary-length reads and writes (divisible by the size) > and do the equivalent of the string I/O instructions outs/ins, but for > the moment I'd like to add the single device that people always seem to > want and can't get from /dev/port. If someone's doing enough writes > that doing a syscall per in/out instruction seems like too much > overhead, they can write a real device driver or use ioperm/iopl. > I really have a problem with the logic "our current interface is wrong, so let's introduce another wrong interface which solves a narrow use case". In some ways it would actually be *better* to use an ioctl interface on /dev/port in that case... -hpa -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
