how hotplug devices onto pcie-to-pci-bridge

[longguang.yue]

Hi, Laine Stump and Oleg Vasilev:
1.  Laine, what is 'conventional PCI device'? in my case they are all virtio device.
2. Followed your guide,succeed in hotplug.  but there are lots of problems after hotplug. I think problems are more related to qemu.
  2.1) disk devices(qcow2,virio) hotpluged onto pci-bridge can not alloc bar resource.
  2.2) disk devices(qcow2,virio) are staticly pluged to pci-bridge can not be found by guest os. 
         those devices are on pci bus, but can not be recognized by guest os, no block device are probed.


qemu qemu-6.2.0
-----hotplug error message--------
[ 1067.577384] pci 0000:06:02.0: [1af4:1001] type 00 class 0x010000
[ 1067.578312] pci 0000:06:02.0: reg 0x10: [io 0x0000-0x007f]
[ 1067.578794] pci 0000:06:02.0: reg 0x14: [mem 0x00000000-0x00000fff]
[ 1067.579419] pci 0000:06:02.0: reg 0x20: [mem 0x00000000-0x00003fff 64bit pref]
[ 1067.581592] pci 0000:06:02.0: BAR 4: no space for [mem size 0x00004000 64bit pref]
[ 1067.581942] pci 0000:06:02.0: BAR 4: failed to assign [mem size 0x00004000 64bit pref]
[ 1067.582264] pci 0000:06:02.0: BAR 1: no space for [mem size 0x00001000]
[ 1067.582625] pci 0000:06:02.0: BAR 1: failed to assign [mem size 0x00001000]
[ 1067.582942] pci 0000:06:02.0: BAR 0: no space for [io size 0x0080]
[ 1067.583253] pci 0000:06:02.0: BAR 0: failed to assign [io size 0x0080]
[ 1067.584019] PCI Interrupt Link [GSIE] enabled at IRQ 20
[ 1067.584749] virtio-pci 0000:06:02.0: virtio_pci: leaving for legacy driver
[ 1067.585296] virtio-pci: probe of 0000:06:02.0 failed with error -12


-------staticly plug------------
[ 0.680299] pci 0000:06:02.0: [1af4:1001] type 00 class 0x010000
[ 0.683035] pci 0000:06:02.0: reg 0x10: [io 0xc080-0xc0ff]
[ 0.688036] pci 0000:06:02.0: reg 0x14: [mem 0xfca01000-0xfca01fff]
[ 0.700040] pci 0000:06:02.0: reg 0x20: [mem 0xfb404000-0xfb407fff 64bit pref]


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At 2022-11-04 05:28:47, "Laine Stump" <laine at laine.org> wrote:
>On 11/3/22 6:35 AM, longguang.yue wrote:
>> Hi, all
>>    I have add two pcie-to-pci-bridge controllers, how hotplug devices 
>> onto this two controllers?  and libvirt knows to plug onto pci-bridge 
>> when there are no pcie-ports.
>> defaultly libvirt plugs devices onto pcie-port.
>
>Do you mean you want hotplugged devices to be placed on the 
>pcie-to-pci-bridge even though there are unused pci-root-ports?
>
>You can force a new device to be hotplugged to a particular slot of a 
>particular controller by including the <address> element in the XML of 
>the device you attach - whatever controller/slot/function you specify 
>there is what libvirt will use (practically speaking the function must 
>be 0).
>
>My recollection is that, *if the device is a conventional PCI device 
>(and not a PCIe device) then libvirt will anyway attempt to find a an 
>open conventional PCI slot, which would be found only on the 
>pcie-to-pci-bridge. However, very few devices are actually conventional 
>PCI, so this will very rarely happen automatically (I haven't looked at 
>that code in a long time, and retain no specific memory, but I think the 
>only emulated device that is conventional PCI is a watchdog device or 
>something)
>
>So, if libvirt is selecting a pcie-root-port to plug in a device, that's 
>because the device is a PCIe device. If you want to force it to do 
>otherwise, you'll need to manually specify the address (just set "bus" 
>of the address to the "index" of the controller, set "slot" to an 
>unoccupied slot (1-31), and set domain and function to 0).
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