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+[[!meta copyright="Copyright © 2010, 2011, 2012, 2013 Free Software Foundation,
+[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
+id="license" text="Permission is granted to copy, distribute and/or modify this
+document under the terms of the GNU Free Documentation License, Version 1.2 or
+any later version published by the Free Software Foundation; with no Invariant
+Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license
+is included in the section entitled [[GNU Free Documentation
+[[!tag open_issue_hurd open_issue_gnumach]]
+# IRC, freenode, #hurd, 2012-07-01
+In context of [[DDE]].
+ <braunr> hm, i haven't looked but, does someone know if virtio is included
+ in netdde ?
+ <youpi> braunr: nope, there's an underlying virtio layer needed before
+# IRC, freenode, #hurd, 2013-07-24
+ <teythoon> btw, I'd love to see libvirt support in hurd
+ <teythoon> I tried to hack up a dde based net translator
+ <teythoon> afaics they are very much like any other pci device, so the
+ infrastructure should be there
+ <teythoon> if anything I expect the libvirt stuff to be more easily
+ portable
+ <youpi> what do you mean by "a dde based net translator" ?
+ <youpi> ah, you mean virtio support in netdde ?
+ <teythoon> yes
+ <teythoon> virtio net is present in the kernel version we use for the dde
+ drivers
+ <teythoon> so I just copied the dde driver over, but I had no luck
+ compiling it
+ <youpi> ok, but what would be the benefice over e1000 & co?
+ <teythoon> any of the dde drivers btw
+ <teythoon> youpi: less overhead
+ <youpi> e1000 is already low overhead actually
+ <youpi> there are less and less differences in strategies for driving a
+ real board, and a virtual one
+ <youpi> we are seeing shared memory request buffer, dma, etc. in real
+ boards
+ <youpi> which ends up being almost exactly what virtio does :)
+ <youpi> ahci, for instance, really looks extremely like a virtio interface
+ <youpi> (I know, it's a disk, but that's the same idea, and I do know what
+ I'm talking about here :) )
+ <teythoon> that would actually be my next wish, a virtio disk driver, and
+ virt9p ;)
+ <braunr> on the other hand, i wouldn't spend much time on a virtio disk
+ driver for now
+ <braunr> the hurd as it is can't boot on a device that isn't managed by the
+ kernel
+ <braunr> we'd need to change the boot protocol
+ <teythoon> ok, I wasn't planning to, just wanted to see if I can easily
+ hack up the virtio-net translator
+ <braunr> well, as youpi pointed, there is little benefit to that as well
+ <braunr> but if that's what you find fun, help yourself :)
+ <teythoon> I didn't know that, I assumed there was some value to the virtio
+ stuff
+ <braunr> there is
+ <braunr> but relatively to other improvements, it's low
+# IRC, freenode, #hurd, 2013-09-14
+ <rekado> I'm slowly beginning to understand the virtio driver framework
+ after reading Rusty's virtio paper and the Linux sources of a few virtio
+ drivers.
+ <rekado> Has anyone started working on virtio drivers yet?
+ <youpi> rekado: nobody has worked on virtio drivers, as I know of
+ <rekado> youpi: I'm still having a hard time figuring out where virtio
+ would fit in in the hurd.
+ <rekado> I'm afraid I don't understand how drivers in the hurd work at all.
+ Will part of this have to be implemented in Mach?
+ <youpi> rekado: it could be implemented either as a Mach driver, or as a
+ userland driver
+ <youpi> better try the second alternative
+ <youpi> i.e. as a translator
+ <youpi> sitting on e.g. /dev/eth0 or /dev/hd0
+## IRC, freenode, #hurd, 2013-09-18
+ <rekado> To get started with virtio I'd like to write a simple driver for
+ the entropy device which appears as a PCI device when running qemu with
+ -device virtio-rng-pci .
+ <braunr> why entropy ?
+ <rekado> because it's the easiest.
+ <braunr> is it ?
+ <braunr> the driver itself may be, but integrating it within the system
+ probably isn't
+ <rekado> It uses the virtio framework but only really consists of a
+ read-only buffer virtqueue
+ <braunr> you're likely to want something that can be part of an already
+ existing subsystem like networking
+ <rekado> All the driver has to do is push empty buffers onto the queue and
+ pass the data it receives back from the host device to the client
+ <rekado> The thing about existing subsystems is: I don't really understand
+ them enough.
+ <rekado> I understand virtio, though.
+ <braunr> but isn't your goal understanding at least one ?
+ <rekado> yes.
+ <braunr> then i suggest working on virtio-net
+ <braunr> and making it work in netdde
+ <rekado> But to write a virtio driver for network I must first understand
+ how to actually talk to the host virtio driver/device.
+ <braunr> rekado: why ?
+ <rekado> There is still a knowledge gap between what I know about virtio
+ and what I have learned about the Hurd/Mach.
+ <braunr> are you trying to learn about virtio or the hurd ?
+ <rekado> both, because I'd like to write virtio drivers for the hurd.
+ <braunr> hm no
+ <rekado> with virtio drivers pass buffers to queues and then notify the
+ host.
+ <braunr> you may want it, but it's not what's best for the project
+ <rekado> oh.
+ <braunr> what's best is reusing existing drivers
+ <braunr> we're much too far from having enough manpower to maintain our own
+ <rekado> you mean porting the linux virtio drivers?
+ <braunr> there already is a virtio-net driver in linux 2.6
+ <braunr> so yes, reuse it
+ <braunr> the only thing which might be worth it is a gnumach in-kernel
+ driver for virtio block devices
+ <braunr> because currently, we need our boot devices to be supported by the
+ kernel itself ...
+ <rekado> when I boot the hurd with qemu and the entropy device I see it as
+ an unknown PCI device in the output of lspci.
+ <braunr> that's just the lspci database which doesn't know it
+ <rekado> Well, does this mean that I could actually talk to the device
+ already? E.g., through libpciaccess?
+ <rekado> I'm asking because I don't understand how exactly devices "appear"
+ on the Hurd.
+ <braunr> it's one of the most difficult topic currently
+ <braunr> you probably can talk to the device, yes
+ <braunr> but there are issues with pci arbitration
+ * rekado takes notes: "pci arbitration"
+ <rekado> so, this is about coordinating bus access, right?
+ <braunr> yes
+ <braunr> i'm not a pci expert so i can't tell you much more
+ <rekado> heh, okay.
+ <rekado> what kind of "issues with pci arbitration" are you referring to,
+ though?
+ <rekado> Is this due to something that Mach isn't doing?
+ <braunr> ideally, mach doesn't know about pci
+ <braunr> the fact we still need in-kernel drivers for pci devices is a big
+ problem
+ <braunr> we may need something like a pci server in userspace
+ <braunr> on l4 system it's called an io server
+ <rekado> How do in-kernel drivers avoid these issues?
+ <braunr> they don't
+ <rekado> Or rather: why is it they don't have these issues?
+ <braunr> they do
+ <rekado> oh.
+ <braunr> we had it when youpi added the sata driver
+ <braunr> so currently, all drivers need to avoid sharing common interrupts
+ for example
+ <braunr> again, since i'm not an expert about pci, i don't know more about
+ the details
+ <Hooligan0> pci arbitrations are made by hardware ... no ?
+ <braunr> Hooligan0: i don't know
+ <braunr> i'm not merely talking about bus mastering here
+ <braunr> simply preventing drivers from mapping the same physical memory
+ should be enforced somewhere
+ <braunr> i'm not sure it is
+ <braunr> same for irq sharing
+ <Hooligan0> braunr : is the support for boot devices into the kernel is
+ really needed if a loader put servers into the memory before starting
+ mach ?
+ <braunr> Hooligan0: there is a chicken-and-egg problem during boot,
+ whatever the solution
+ <braunr> obviously, we can preload from memory, but then you really want
+ your root file system to use a disk
+ <braunr> Hooligan0: the problem with preloading from memory is that you
+ want the root file system to use a real device
+ <braunr> the same way / refers to one on unix
+ <braunr> so you have an actual, persistent hierarchy from which the system
+ can be initialized and translators started
+ <braunr> you also want to share as much as possible between the early
+ programs and the others
+ <braunr> so for example, both the disk driver and the root file system
+ should be able to use the same libc instance
+ <braunr> this requires a "switch root" mechanism that needs to be well
+ defined and robust
+ <braunr> otherwise we'd just build our drivers and root fs statically
+ <braunr> (which is currently done with rootfs actually)
+ <braunr> and this isn't something we're comfortable with
+ <braunr> so for now, in-kernel drivers
+ <Hooligan0> humm ... disk driver and libc ... i see
+ <Hooligan0> in other way ... disk drivers can use only a little number of
+ lib* functions ; so with a static version, a bit of memory is lots
+ <Hooligan0> s/lots/lost
+ <Hooligan0> and maybe the driver can be hot-replaced after boot (ok ok,
+ it's more simple to say than to write)
+<a name="KVM"></a>
+# Virtio Drivers for KVM
+In context of [[hurd/running/cloud]], *OpenStack*.
+Ideally they would be userland. That means getting documentation about how
+virtio works, and implement it. The hurdish part is mostly about exposing the
+driver interface. The [[hurd/translator/devnode]] translator can be used as a