Re: How to best make include/hw/pci/pcie_sriov.h self-contained

[Michael S. Tsirkin]

On Wed, Dec 07, 2022 at 07:25:49AM +0100, Markus Armbruster wrote:
> pcie_sriov.h needs PCI_NUM_REGIONS from pci.h, but doesn't include it.
> pci.h must be included before pcie_sriov.h or else compile fails.
> 
> Adding #include "pci/pci.h" to pcie_sriov would be wrong, because it
> would close an inclusion loop: pci.h includes pcie.h (for
> PCIExpressDevice) includes pcie_sriov.h (for PCIESriovPF) includes pci.h
> (for PCI_NUM_REGIONS).
> 
> The obvious solution is to move PCI_NUM_REGIONS pci.h somewhere
> pcie_sriov.h can include without creating a loop.
> 
> We already have a few headers that don't include anything: pci_ids.h,
> pci_regs.h (includes include/standard-headers/linux/pci_regs.h, which
> doesn't count), pcie_regs.h.  Moving PCI_NUM_REGIONS to one of these
> would work, but it doesn't feel right.
> 
> We could create a new one, say pci_defs.h.  Just for PCI_NUM_REGIONS
> feels silly.  So, what else should move there?

I'm ok with pci_defs.h
However, I note that most headers including pci.h don't really
need it. Consider include/hw/virtio/virtio-iommu.h all it needs is
PCIBus typedef this is available from qemu/typedefs.h
So if you are poking at this, want to clean that area up generally?

> Any other ideas?
> 
> In case you wonder why I bother you with this...
> 
> Back in 2016, we discussed[1] rules for headers, and these were
> generally liked:
> 
> 1. Have a carefully curated header that's included everywhere first.  We
>    got that already thanks to Peter: osdep.h.
> 
> 2. Headers should normally include everything they need beyond osdep.h.
>    If exceptions are needed for some reason, they must be documented in
>    the header.  If all that's needed from a header is typedefs, put
>    those into qemu/typedefs.h instead of including the header.
> 
> 3. Cyclic inclusion is forbidden.
> 
> I'm working on patches to get include/ closer to obeying 2.
> 
> [1] Message-ID: <87h9g8j57d.fsf@blackfin.pond.sub.org>
>     https://lists.nongnu.org/archive/html/qemu-devel/2016-03/msg03345.html