Then the question is whether the kernel is copying data between userspace
and kernelspace or whether it just DMAs the data straight in/out of the
user program's address space. In Linux raw-io, given that it is a block
device and you are doing page-aligned block I/Os on it, is smart and does
zero copies. While it may seem to be jumping through hoops, maybe it does
have a performance advantage?
Regards,
-Kevin.
On Wed, 4 Jul 2001, Kenneth D. Merry wrote:
> On Wed, Jul 04, 2001 at 17:58:58 -0400, Kevin Hui wrote:
> > Hi all,
> >
> > I'm wondering if *BSD have any support for user programs to access raw
> > disk devices, unbuffered. Such support is available under Linux:
> >
> > http://www.kernel.org/LDP/HOWTO/SCSI-2.4-HOWTO/rawdev.html
> > http://www2.linuxjournal.com/cgi-bin/linux/man.cgi?mode=search&comm=raw§=1
> >
> > Any information regarding this would be appreciated.
>
> There are no block (i.e. buffered) devices in FreeBSD, only character
> devices.
>
> So you can access raw devices without having to go through all the hoops
> described above.
>
> Ken
> --
> Kenneth Merry
> [EMAIL PROTECTED]
>
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