Re: [Xen-devel] [RFC 0/7] Move accel, KVM, Xen, qtest files to accel/ subdir

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

On 20/12/2016 18:43, Eduardo Habkost wrote:
> This moves the KVM and Xen files to the an accel/ subdir.
> 
> Instead of moving the *-stubs.c file to accel/ as-is, I tried to
> move most of the stub code to libqemustub.a. This way the obj-y
> logic for accel/ is simpler: obj-y includes accel/ only if
> CONFIG_SOFTMMU is set.
> 
> The Xen stubs could be moved completely to stubs/, but some of
> the KVM stubs depend on cpu.h. So most of the kvm-stub.c code was
> moved to stubs/kvm.c, but some of that code was kept in
> accel/kvm-stub.c.

I think we need to decide what libqemustub is for.

The original purpose was to provide different implementations of some
functions for tools vs. emulators or (more rarely) for user-mode vs.
system emulation.

There are also some cases where we use it for functions that are only
implemented by some targets.

In general, I think libqemustub should be the last resort.  If possible,
inlines in headers should be the first choice, and stubs in objs-y or
common-objs-y (using $(call lnot) in the Makefile) should be the second.

The reason is that stubs/ hides files from the corresponding maintainer;
for example, commit 07a32d6b's addition of stubs/get-next-serial.c was
in all likelihood unnecessary, but the new file went in without an ack
for a character device maintainer.  Tracking stubs in the MAINTAINERS
file is unwieldy and, from this point of view, I find

        F: accel/kvm*

to be preferrable to

        F: accel/kvm*
        F: stubs/kvm.c

Thanks,

Paolo

> About TCG:
> ----------
> 
> It is not obvious to me which TCG-related files could be moved to
> accel/, so this series don't move any of them yet.
> 
> About other CONFIG_SOFTMMU top-level files:
> -------------------------------------------
> 
> I would like to know what we should do with the top-level
> CONFIG_SOFTMMU-only files that don't belong to hw/. Some
> candidates: arch_init.c cpus.c monitor.c gdbstub.c balloon.c
> ioport.c bootdevice.c memory.c cputlb.c memory_mapping.c dump.c.
> 
> Maybe a sysemu/ subdir? In that case, should we still create an
> accel/ subdir, or move xen-*, kvm-* and friends to sysemu/ too?
> 
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx
> Cc: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
> 
> Eduardo Habkost (7):
>   xen: Move xen-*-stub.c to stubs/
>   xen: Move xen files to accel/
>   kvm: Move some kvm-stub.c code to stubs/kvm.c
>   kvm: Include kvm-stub.o only on CONFIG_SOFTMMU
>   kvm: Move kvm*.c files to accel/
>   accel: Move accel.c to accel/
>   accel: Move qtest.c to accel/

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