Re: direct I/O access

On Thu, 31 May 2007 08:44:33 +0400
Eygene Ryabinkin <rea-fbsd@xxxxxxxxxxx> wrote,
Wed, May 30, 2007 at 02:43:07AM -0400, Mike Meyer wrote:

I believe this should be $0x4, as you want to *set* the values, not
get them.

Right.

You also need to open the file "/dev/io". I believe that leaving this
file open for anything more than a handful of instructions would be a
bad thing, but I'm not going to verify it.

I feel that the i386_set_ioperm directly manipulates the task's I/O
bitmap referenced by the task state segment (TSS), so you don't
need to mangle with /dev/io. /dev/io itself is the higher-level
semi machine-indenepdent abstraction. Opening /dev/io grants the
global access to all ports, while using i386_set_ioperm gives the
fine-grained access. When you closing /dev/io, the port I/O access
is revoked.

To summarise: either you open /dev/io and do all your port I/O as
in the good old days of the real-mode programs, or you're using
i386_set_ioperm to obtain the access permissions to the I/O port
range and again, do all port I/O as usual.

i rewrote my code and this time, all works fine.
thanks to Mike and Eygene.

here is the code as a proof of the above explanation:

# test_io.S

.include "system.inc"

BUFSIZE = 0x80

.data
params: .long 0x70,2,1,0
path: .asciz "/dev/io"

.bss
buffer: .fill BUFSIZE, 0


.text
.global _start

err:
pushl $0x1 # return failure
SysExit


_start:
addl $8,%esp # discard argc and argv[0]

leal params,%eax
pushl %eax
pushl $4
movl $0xa5,%eax
call bsd_kernel
addl $12,%esp


movl $0X330,%edx
inb %dx,%al
# if i try to read or write another port than 0x70/0x71, i have a segbus fault.

leal path,%ecx
pushl $0 # O_RDONLY
pushl %ecx
SysOpen
jc err # open failed
addl $8,%esp
movl $0X330,%edx
inb %dx,%al
# all is ok!

pushl $0 # return success
SysExit

Thanks again.

Raoul
rmgls@xxxxxxxxxx

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