linux-kernel - Re: [PATCH] [v2] blkdev: always export SECTOR

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Message-ID: <CAK8P3a09YuLbQrfC61VMg_v3h+pA-QZBnW7i45AG6asPgMuoGg@mail.gmail.com>
Date:   Fri, 19 Jul 2019 15:14:52 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christoph Hellwig <hch@....de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.com>,
        Omar Sandoval <osandov@...com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH] [v2] blkdev: always export SECTOR_SHIFT

On Fri, Jul 19, 2019 at 2:13 PM Christoph Hellwig <hch@....de> wrote:
>
> > +/*
> > + * The basic unit of block I/O is a sector. It is used in a number of contexts
> > + * in Linux (blk, bio, genhd). The size of one sector is 512 = 2**9
> > + * bytes. Variables of type sector_t represent an offset or size that is a
> > + * multiple of 512 bytes. Hence these two constants.
> > + */
> > +#ifndef SECTOR_SHIFT
> > +#define SECTOR_SHIFT 9
> > +#endif
> > +#ifndef SECTOR_SIZE
> > +#define SECTOR_SIZE (1 << SECTOR_SHIFT)
> > +#endif
>
> While we're at it we really should drop the ifndefs.

Good idea. Needs some more build testing then.

> Otherwise looks good.
>
> In fact given that sector_t is in linux/types.h I wonder if these
> should just move there.

Less sure about that, we don't really have other constants in that
file, just typedefs and a few common structures.

    ARnd