From: Barry Song <21cnbao@gmail.com>
To: Meiyong Yu <meiyong.yu@126.com>
Cc: corbet@lwn.net, workflows@vger.kernel.org,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
Barry Song <v-songbaohua@oppo.com>,
Andrew Morton <akpm@linux-foundation.org>,
Chris Zankel <chris@zankel.net>,
Huacai Chen <chenhuacai@loongson.cn>,
Herbert Xu <herbert@gondor.apana.org.au>,
Guenter Roeck <linux@roeck-us.net>,
Max Filippov <jcmvbkbc@gmail.com>
Subject: Re: [PATCH] Documentation: coding-style: ask function-like macros to evaluate parameters
Date: Thu, 21 Mar 2024 20:42:38 +1300 [thread overview]
Message-ID: <CAGsJ_4yoYjt__kvQd6snZeOYLxz9=N2S929+amZYiZvSNLgs+g@mail.gmail.com> (raw)
In-Reply-To: <7bdc4d24-adfd-4a8c-b824-6833149f5636@126.com>
On Thu, Mar 21, 2024 at 5:40 PM Meiyong Yu <meiyong.yu@126.com> wrote:
>
>
> 在 2024/3/21 8:11, Barry Song 写道:
> > On Thu, Mar 21, 2024 at 12:39 PM Meiyong Yu <meiyong.yu@126.com> wrote:
> >>
> >>> On Mar 20, 2024, at 08:17, Barry Song <21cnbao@gmail.com> wrote:
> >>>
> >>> From: Barry Song <v-songbaohua@oppo.com>
> >>>
> >>> Recent commit 77292bb8ca69c80 ("crypto: scomp - remove memcpy if
> >>> sg_nents is 1 and pages are lowmem") leads to warnings on xtensa
> >>> and loongarch,
> >>> In file included from crypto/scompress.c:12:
> >>> include/crypto/scatterwalk.h: In function 'scatterwalk_pagedone':
> >>> include/crypto/scatterwalk.h:76:30: warning: variable 'page' set but not used [-Wunused-but-set-variable]
> >>> 76 | struct page *page;
> >>> | ^~~~
> >>> crypto/scompress.c: In function 'scomp_acomp_comp_decomp':
> >>>>> crypto/scompress.c:174:38: warning: unused variable 'dst_page' [-Wunused-variable]
> >>> 174 | struct page *dst_page = sg_page(req->dst);
> >>> |
> >>>
> >>> The reason is that flush_dcache_page() is implemented as a noop
> >>> macro on these platforms as below,
> >>>
> >>> #define flush_dcache_page(page) do { } while (0)
> >>>
> >>> The driver code, for itself, seems be quite innocent and placing
> >>> maybe_unused seems pointless,
> >>>
> >>> struct page *dst_page = sg_page(req->dst);
> >>>
> >>> for (i = 0; i < nr_pages; i++)
> >>> flush_dcache_page(dst_page + i);
> >>>
> >>> And it should be independent of architectural implementation
> >>> differences.
> >>>
> >>> Let's have a guidance in codingstyle to ask for the evaluation
> >>> of parameters.
> >>>
> >>> Cc: Andrew Morton <akpm@linux-foundation.org>
> >>> Cc: Chris Zankel <chris@zankel.net>
> >>> Cc: Huacai Chen <chenhuacai@loongson.cn>
> >>> Cc: Herbert Xu <herbert@gondor.apana.org.au>
> >>> Cc: Guenter Roeck <linux@roeck-us.net>
> >>> Suggested-by: Max Filippov <jcmvbkbc@gmail.com>
> >>> Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> >>> ---
> >>> Documentation/process/coding-style.rst | 7 +++++++
> >>> 1 file changed, 7 insertions(+)
> >>>
> >>> diff --git a/Documentation/process/coding-style.rst b/Documentation/process/coding-style.rst
> >>> index 9c7cf7347394..8065747fddff 100644
> >>> --- a/Documentation/process/coding-style.rst
> >>> +++ b/Documentation/process/coding-style.rst
> >>> @@ -827,6 +827,13 @@ Macros with multiple statements should be enclosed in a do - while block:
> >>> do_this(b, c); \
> >>> } while (0)
> >>>
> >>
> >>> +Function-like macros should evaluate their parameters, for unused parameters,
> >> I do not support this point, if the parameter is unused, why not to remove it.
> >>
> > Linux boasts support for numerous architectures, striving for
> > independence in its
> > drivers and core code implementation across these architectures. Consequently,
> > certain architectures may utilize parameters for the same APIs, while others may
> > not.
>
> So the probem is designed api is not reasonable, it use not essential
> paramter,
>
> you can change the api, but not avoid it.
>
Incorrect again. As an API, it must take into account various considerations.
Just because architecture A doesn't require flushing dcache doesn't imply
that architecture B doesn't need it.
> Anthor question, why you do not use the parameter, if not use it, will
> trigger function/feature dismiss problem ?
>
> >> about the warning, is tool misreport, the tool must make better
> >>
> > no. This is not the case.
> >
> >>> +cast them to void:
> >>> +
> >>> +.. code-block:: c
> >>> +
> >>> + #define macrofun(a) do { (void) (a); } while (0)
> >>> +
> >>> Things to avoid when using macros:
> >>>
> >>> 1) macros that affect control flow:
> >>> --
> >>> 2.34.1
> >>>
> >>
>
>
prev parent reply other threads:[~2024-03-21 7:42 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-03-20 0:16 [PATCH] Documentation: coding-style: ask function-like macros to evaluate parameters Barry Song
2024-03-20 1:42 ` Stephen Rothwell
2024-03-20 3:24 ` Barry Song
2024-03-20 3:45 ` Stephen Rothwell
2024-03-20 15:49 ` Andrew Morton
2024-03-20 18:48 ` Barry Song
2024-03-21 11:15 ` Mark Brown
2024-03-21 20:29 ` Barry Song
2024-03-21 17:44 ` Andrew Morton
2024-03-20 23:37 ` Meiyong Yu
2024-03-21 0:11 ` Barry Song
2024-03-21 4:38 ` Meiyong Yu
2024-03-21 7:42 ` Barry Song [this message]
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