Date: Tue, 16 Feb 1999 15:26:04 -0700 From: Wes Peters <wes@softweyr.com> To: Donn Miller <dmm125@bellatlantic.net> Cc: hackers@FreeBSD.ORG Subject: Re: Systems programming for FreeBSD Message-ID: <36C9F07C.7F2C9367@softweyr.com> References: <36C8C170.4AA85CA@bellatlantic.net>
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Donn Miller wrote:
>
> I'm looking for some info on how to use functions like inb() and outb()
> to do systems-level programming on FreeBSD.
>
> 1.) I need to know the FreeBSD equiv. of the Linux function ioperm().
> I would think you just use open() on /dev/pio or /dev/io with the
> appropriate permissions.
"man io" tells us:
IO(4) FreeBSD Kernel Interfaces Manual (i386 Architecture) IO(4)
NAME
io - I/O privilege file
DESCRIPTION
The special file /dev/io is a controlled security hole that allows a pro-
cess to gain I/O privileges (which are normally reserved for kernel-
internal code). Any process that holds a file descriptor on /dev/io open
will get its IOPL bits in the flag register set, thus allowing it to per-
form direct I/O operations. This can be useful in order to write user-
land programs that handle some hardware directly.
The entire access control is handled by the file access permissions of
/dev/io, so care should be taken in granting rights for this device.
Note that even read/only access will grant the full I/O privileges.
FILES
/dev/io
SEE ALSO
mem(4)
HISTORY
The io file appeared in FreeBSD 1.0.
>
> 2.) what include files do I need to use to use inb() and outb()? In
> Linux it's <asm/io.h>
machine/cpufunc.h
> Is using ports my only/best option for doing systems-level programming
> for writing drivers for video cards, or should I use assembly?
Ports are your only choice when doing port-mapped I/O. Using assembler
will make your driver run faster, IF you are a good assembly programmer.
If not, you'll probably be better off writing C.
If you want to write a driver for a video card, start with one of the
existing drivers for a similar device.
> There's a Linux howto on systems programming, maybe FreeBSD is similar
> in that respect. so I can just use the Linux howto for FreeBSD. What
> are ports anyway, is it like you're writing to a special part of memory?
No, I/O ports are a separate address space from memory. I strongly
suggest a good book on x86 architecture, but don't have any idea
what one might be. Mine is ages old and probably isn't published
anymore.
Suggestions, hackers?
--
Where am I, and what am I doing in this handbasket?
Wes Peters +1.801.915.2061
Softweyr LLC wes@softweyr.com
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