linux-kernel - Re: [PATCH 04/16] bvec: add a bvec_kmap

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Date:   Wed, 9 Jun 2021 11:33:13 +0200
From:   Ilya Dryomov <idryomov@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geoff Levand <geoff@...radead.org>,
        Dongsheng Yang <dongsheng.yang@...ystack.cn>,
        Mike Snitzer <snitzer@...hat.com>,
        Ira Weiny <ira.weiny@...el.com>, dm-devel@...hat.com,
        linux-mips@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org,
        Ceph Development <ceph-devel@...r.kernel.org>
Subject: Re: [PATCH 04/16] bvec: add a bvec_kmap_local helper

On Tue, Jun 8, 2021 at 6:06 PM Christoph Hellwig <hch@....de> wrote:
>
> Add a helper to call kmap_local_page on a bvec.  There is no need for
> an unmap helper given that kunmap_local accept any address in the mapped
> page.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  include/linux/bvec.h | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/include/linux/bvec.h b/include/linux/bvec.h
> index 883faf5f1523..d64d6c0ceb77 100644
> --- a/include/linux/bvec.h
> +++ b/include/linux/bvec.h
> @@ -7,6 +7,7 @@
>  #ifndef __LINUX_BVEC_H
>  #define __LINUX_BVEC_H
>
> +#include <linux/highmem.h>
>  #include <linux/bug.h>
>  #include <linux/errno.h>
>  #include <linux/limits.h>
> @@ -183,4 +184,9 @@ static inline void bvec_advance(const struct bio_vec *bvec,
>         }
>  }
>
> +static inline void *bvec_kmap_local(struct bio_vec *bvec)
> +{
> +       return kmap_local_page(bvec->bv_page) + bvec->bv_offset;
> +}
> +
>  #endif /* __LINUX_BVEC_H */

Might be useful to add the second sentence of the commit message as
a comment for bvec_kmap_local().  It could be expanded to mention the
single-page bvec caveat too.

Thanks,

                Ilya