From: Kevin Hui <khui@cs.toronto.edu> To: "Kenneth D. Merry" <ken@kdm.org> Cc: freebsd-questions@FreeBSD.ORG, freebsd-hackers@FreeBSD.ORG Subject: Re: Raw disk access in userland Message-ID: <Pine.GSO.4.21.0107042015130.5050-100000@gardiner.cs> In-Reply-To: <20010704170844.A47113@panzer.kdm.org>
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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 > ken@kdm.org > To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message
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