[Qemu-devel] Re: [RFC] Bring in all the Linux headers we depend on in QEMU

[Arnd Bergmann]

On Sunday 03 May 2009, Anthony Liguori wrote:
> A classic example is linux/compiler.h and the broken usbdevice_fs.h
> header that depends on it.  There are still distributions today that
> QEMU doesn't compile on because of this.

Can you clarify this? I can't find any version of usbdevice_fs.h that
ever included linux/compiler.h (make headers_check would warn about that),
and the only construct used in there that comes from compiler.h is
the __user annotation, which gets stripped in 'make headers_install',
and has been since 2006.

 > +# Linux kernel headers CFLAGS
> +if test -z "$kerneldir" ; then
> +    linux_cflags="-I$source_path/linux"
> +else
> +    linux_cflags="-I$kerneldir/include"
> +    if test \( "$cpu" = "i386" -o "$cpu" = "x86_64" \) \
> +       -a -d "$kerneldir/arch/x86/include" ; then
> +       linux_cflags="$linux_cflags -I$kerneldir/arch/x86/include"
> +    elif test "$cpu" = "ppc" -a -d "$kerneldir/arch/powerpc/include" ;
> then +       linux_cflags="$linux_cflags -I$kerneldir/arch/powerpc/include"
> +    elif test -d "$kerneldir/arch/$cpu/include" ; then
> +       linux_cflags="$linux_cflags -I$kerneldir/arch/$cpu/include"
> +    fi
> +fi

arch/*/include is not the right place to look for user headers.
I think it would be better to assume that the user only points to
valid exported headers, so look for linux/version.h to check that
the files have been configured and look for the absense of
kvm_host.h to make sure that the user did not point to plain
kernel sources.

The exported headers already handle the asm/ links correctly, so
I think you never need to do anything architecture specific
like your fixup.sed.

> +CORE_HDRS=linux/types.h linux/posix_types.h linux/stddef.h linux/compiler.h
> +CORE_HDRS+=linux/byteorder/little_endian.h linux/byteorder/big_endian.h
> +CORE_HDRS+=linux/swab.h linux/ioctl.h
> +
> +CORE_HDRS+=asm-generic/int-ll64.h asm-generic/int-l64.h asm-generic/ioctl.h
> +
> +CORE_HDRS+=asm-x86/types.h asm-x86/posix_types.h
> +CORE_HDRS+=asm-x86/posix_types_32.h asm-x86/posix_types_64.h
> +CORE_HDRS+=asm-x86/byteorder.h asm-x86/swab.h asm-x86/ioctl.h
> +
> +CORE_HDRS+=asm-powerpc/types.h asm-powerpc/posix_types.h
> +CORE_HDRS+=asm-powerpc/byteorder.h asm-powerpc/swab.h asm-powerpc/ioctl.h
> +
> +CORE_HDRS+=asm-sparc/types.h asm-sparc/posix_types.h
> +CORE_HDRS+=asm-sparc/byteorder.h asm-sparc/swab.h asm-sparc/ioctl.h
> +CORE_HDRS+=asm-sparc/asi.h 
> +
> +CORE_HDRS+=asm-arm/types.h asm-arm/posix_types.h
> +CORE_HDRS+=asm-arm/byteorder.h asm-arm/swab.h asm-arm/ioctl.h
> +
> +CORE_HDRS+=asm-parisc/types.h asm-parisc/posix_types.h
> +CORE_HDRS+=asm-parisc/byteorder.h asm-parisc/swab.h asm-parisc/ioctl.h

I don't see the need to copy all the core headers. These should have
been working for ages, and hardly ever see changes that are relevant
to kvm. 

The exceptions are linux/stddef.h and linux/compiler.h, which are
not exported and should never be used outside of the kernel.

> +# Kernel Virtual Machine interface
> +KVM_HDRS=linux/kvm.h linux/kvm_para.h
> +KVM_HDRS+=asm-x86/kvm.h asm-x86/kvm_para.h
> +KVM_HDRS+=asm-powerpc/kvm.h asm-powerpc/kvm_para.h
> +
> +# VirtIO paravirtual IO framework
> +VIRTIO_HDRS=linux/virtio_config.h linux/virtio_net.h linux/virtio_blk.h
> +VIRTIO_HDRS+=linux/virtio_console.h linux/virtio_balloon.h

These should be copied into the qemu source tree, but not at configure
time. They should just reflect the latest upstream version. Qemu already
needs to handle older kernel versions at run time, and by having the
very latest version in the source tree, you can make sure that qemu
will run on any kernel version.

For asm/kvm.h and asm/kvm-para.h, you can have hard-coded files
multiplexing between the architectures, as you would otherwise
generate from your fixup.sed.

> +# tun/tap interfaces
> +TUN_HDRS=linux/if_tun.h linux/if_ether.h
> +
> +# timers
> +TIMER_HDRS=linux/rtc.h linux/hpet.h
> +
> +# USB pass through
> +USB_HDRS=linux/usbdevice_fs.h linux/magic.h
> +
> +# IDE/FD
> +DISK_HDRS=linux/cdrom.h linux/fd.h
> +
> +# Parallel port
> +PPORT_HDRS=linux/ppdev.h linux/parport.h

For all of these, I would again fall back on the distro-provided
headers. You might not get the latest versions, but at least you
can assume that any kernel that the distro provides will also
at least support the ABI from these headers.

        Arnd <><