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Date:   Thu, 14 Jul 2022 14:33:17 +0200
From:   David Sterba <dsterba@suse.cz>
To:     Wang Yugui <wangyugui@e16-tech.com>
Cc:     "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
        Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>,
        Nick Terrell <terrelln@fb.com>, linux-btrfs@vger.kernel.org,
        linux-kernel@vger.kernel.org, Filipe Manana <fdmanana@kernel.org>,
        Ira Weiny <ira.weiny@intel.com>
Subject: Re: [PATCH] btrfs: Replace kmap() with kmap_local_page() in zstd.c
Message-ID: <20220714123317.GI15169@suse.cz>
Reply-To: dsterba@suse.cz
Mail-Followup-To: dsterba@suse.cz, Wang Yugui <wangyugui@e16-tech.com>,
        "Fabio M. De Francesco" <fmdefrancesco@gmail.com>,
        Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>, Nick Terrell <terrelln@fb.com>,
        linux-btrfs@vger.kernel.org, linux-kernel@vger.kernel.org,
        Filipe Manana <fdmanana@kernel.org>,
        Ira Weiny <ira.weiny@intel.com>
References: <20220611135203.27992-1-fmdefrancesco@gmail.com>
 <20220714082519.A7C9.409509F4@e16-tech.com>
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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.