GEOM Gate committed!

[Pawel Jakub Dawidek]

Hello.

I committed GEOM Gate. For those who aren't aware of what it is, few words
of explanation.

GEOM Gate itself (as a GEOM class) is a bridge between GEOM and userland
applications that want to handle I/O requests in userland.
Such an application is able to create a ggate provider by ioctl(2)
mechnism and receive I/O requests directed to this newly created
provider.

I committed 3 applications that made use of GEOM Gate:

	ggatel(8) - GEOM Gate local control utility.
	ggatec(8) - GEOM Gate network client and control utility.
	ggated(8) - GEOM Gate network daemon.

Ggatel is only an example for programmers how to use GEOM Gate
mechanism, but it could also be used as an replacement for md(4)
file-backed devices or as a "GEOMificator" for not GEOM-aware
disk devices. For example, one is not able use gbde(8) on floppy
disks, with ggatel(8) it is possible:

	# ggatel create -u 5 /dev/fd0
	# gbde init /dev/ggate5
	# gbde attach ggate5
	# newfs /dev/ggate5.bde
	# mount /dev/ggate5.bde /secret
	# cp /private/foo /secret/
	# umount /secret
	# gbde detach ggate5
	# ggatel destroy -u 5

Anyway. More interesting use is disk device (or files) exporting through
the network. Here is an example how to use CD-ROM from machine 'server'
on machine 'client':

	server# echo "10.0.0.0/8 RO /dev/acd0" > /etc/gg.exports
	server# ggated

	client# ggatec create -u 5 server.mydomain /dev/acd0
	client# mount_cd9660 /dev/ggate5 /cdrom

That was easy. While playing with GEOM Gate I decided to test
'make -j2 buildkernel' on GENERIC kernel:

	1: 559s
	2: 560s
	3: 729s
where:
	1 - /usr/src and /usr/obj on local /dev/data.stripe, which
	    is two SATA disks striped (~118MB/s).
	2 - /usr/src is on SATA disk /dev/ad6, /usr/obj is on SATA
	    disk /dev/ad8, but both disks are exported through 1Gbit
	    network with GEOM Gate and used on test machine.
	3 - Simlar situation to 2, but /usr/src and /usr/obj are
	    mounted over NFS.
Interesting. It shows not only that GEOM Gate is faster that NFS
(what I wanted to proof), but also that disk speed isn't so
important. I get ~35MB/s on ggate devices over 1Gbit network.

We can do some optimizations in the future, for example instead of
copying data from kernel to userland, we should map bio_data into
userland process, but I'm not a VM guru to do this.

Thing to note: ggated(8) is absolutely GEOM-unaware and not FreeBSD
specific at all. It is a simple network daemon that opens given device
or file and read from/write to it, that's all. So it should be really
trivial to port it to other operating systems and exports disk devices
from them.

Comments, suggestion, bug reports are of course more than welcome.
Enjoy!

-- 
Pawel Jakub Dawidek                       http://www.FreeBSD.org
pjd at FreeBSD.org                           http://garage.freebsd.pl
FreeBSD committer                         Am I Evil? Yes, I Am!
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