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. - Josh triplett -- 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
