linux-kernel - Re: [PATCH] btrfs: Replace kmap() with kmap_local

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Message-ID: <20220714123317.GI15169@suse.cz>
Date:   Thu, 14 Jul 2022 14:33:17 +0200
From:   David Sterba <dsterba@...e.cz>
To:     Wang Yugui <wangyugui@...-tech.com>
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>,
        Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        Nick Terrell <terrelln@...com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org, Filipe Manana <fdmanana@...nel.org>,
        Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH] btrfs: Replace kmap() with kmap_local_page() in zstd.c

On Thu, Jul 14, 2022 at 08:25:20AM +0800, Wang Yugui wrote:
> Hi,
> 
> Compiler warning:
> 
> fs/btrfs/zstd.c:478:55: warning: passing argument 1 of ‘__kunmap_local’ discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
>   478 |                         kunmap_local(workspace->in_buf.src);
> ./include/linux/highmem-internal.h:284:24: note: in definition of macro ‘kunmap_local’
>   284 |         __kunmap_local(__addr);                                 \
>       |                        ^~~~~~
> ./include/linux/highmem-internal.h:200:41: note: expected ‘void *’ but argument is of type ‘const void *’
>   200 | static inline void __kunmap_local(void *addr)
>       |                                   ~~~~~~^~~~

This requires patch
https://lore.kernel.org/all/20220706111520.12858-2-fmdefrancesco@gmail.com/
that adds const to kmap/kunmap API.