Re: [PATCH v2] Avoid address_space_rw() with a constant is_write argument

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 18 Feb 2020 11:24:57 +0000
Peter Maydell <peter.maydell@linaro.org> wrote:

> The address_space_rw() function allows either reads or writes
> depending on the is_write argument passed to it; this is useful
> when the direction of the access is determined programmatically
> (as for instance when handling the KVM_EXIT_MMIO exit reason).
> Under the hood it just calls either address_space_write() or
> address_space_read_full().
> 
> We also use it a lot with a constant is_write argument, though,
> which has two issues:
>  * when reading "address_space_rw(..., 1)" this is less
>    immediately clear to the reader as being a write than
>    "address_space_write(...)"
>  * calling address_space_rw() bypasses the optimization
>    in address_space_read() that fast-paths reads of a
>    fixed length
> 
> This commit was produced with the included Coccinelle script
> scripts/coccinelle/as-rw-const.patch.
> 
> Two lines in hw/net/dp8393x.c that Coccinelle produced that
> were over 80 characters were re-wrapped by hand.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> ---
> I could break this down into separate patches by submaintainer,
> but the patch is not that large and I would argue that it's
> better for the project if we can try to avoid introducing too
> much friction into the process of doing 'safe' tree-wide
> minor refactorings.
> 
> v1->v2: put the coccinelle script in scripts/coccinelle rather
> than just in the commit message.
> ---
>  accel/kvm/kvm-all.c                  |  6 +--
>  dma-helpers.c                        |  4 +-
>  exec.c                               |  4 +-
>  hw/dma/xlnx-zdma.c                   | 11 ++---
>  hw/net/dp8393x.c                     | 68 ++++++++++++++--------------
>  hw/net/i82596.c                      | 25 +++++-----
>  hw/net/lasi_i82596.c                 |  5 +-
>  hw/ppc/pnv_lpc.c                     |  8 ++--
>  hw/s390x/css.c                       | 12 ++---

s390 part:

Reviewed-by: Cornelia Huck <cohuck@redhat.com>

>  qtest.c                              | 52 ++++++++++-----------
>  target/i386/hvf/x86_mmu.c            | 12 ++---
>  scripts/coccinelle/as_rw_const.cocci | 30 ++++++++++++
>  12 files changed, 133 insertions(+), 104 deletions(-)
>  create mode 100644 scripts/coccinelle/as_rw_const.cocci