Re: [libvirt] [PATCH] docs: Improve PCI topology and hotplug guidelines

Address some minor flaws in the original document that were pointed out during review. Signed-off-by: Andrea Bolognani <abologna(a)redhat.com&gt; --- docs/pci-hotplug.html.in | 46 ++++++++++++++++++++++++++++++++-------------- 1 file changed, 32 insertions(+), 14 deletions(-) diff --git a/docs/pci-hotplug.html.in b/docs/pci-hotplug.html.in index 809e36f5d..a90d47bc3 100644 --- a/docs/pci-hotplug.html.in +++ b/docs/pci-hotplug.html.in @@ -13,10 +13,12 @@ <p> The reason for this apparent limitation is the fact that each hotplugged PCI device might require additional PCI controllers to - be added to the guest, and libvirt has no way of knowing in advance - how many devices will be hotplugged during the guest's lifetime, - thus making it impossible to automatically provide the right amount - of PCI controllers: any arbitrary number would end up being too big + be added to the guest. Since most PCI controllers can't be + hotplugged, they need to be added before the guest is started; + however, libvirt has no way of knowing in advance how many devices + will be hotplugged during the guest's lifetime, thus making it + impossible to automatically provide the right amount of PCI + controllers: any arbitrary number would end up being too big for some users, and too small for others. </p> <p> @@ -53,6 +55,14 @@ emulated or assigned from the host. </p> <p> + If you have a very specialized use case, such as the appliances

+ used by <a href="http://libguestfs.org/">libguestfs</a> behind + the scenes to access disk images, and this automatically-added + <code>pcie-root-port</code> controller ends up being a nuisance, + you can prevent libvirt from adding it by manually managing PCI + controllers and addresses according to you needs.

+ </p> + <p> Slots on the <code>pcie-root</code> controller do not support hotplug, so the device will be hotplugged into the <code>pcie-root-port</code> controller. If you plan to hotplug @@ -73,6 +83,12 @@ remaining details automatically. </p> <p> + Note that if you're adding PCI controllers to a guest at the + same time you're also adding PCI devices, some of the

+ controllers will be used for the newly-added devices and won't + be available for hotplug once the guest has been started. + </p> + <p> If you expect to hotplug legacy PCI devices, then you will need specialized controllers, since all those mentioned above are