linux-ext4 - Re: don't use ->bd_inode to access the block device size

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Date:   Thu, 14 Oct 2021 09:32:58 +0000
From:   Anton Altaparmakov <anton@...era.com>
To:     Christoph Hellwig <hch@....de>
CC:     Jens Axboe <axboe@...nel.dk>, Coly Li <colyli@...e.de>,
        Mike Snitzer <snitzer@...hat.com>, Song Liu <song@...nel.org>,
        David Sterba <dsterba@...e.com>,
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        Theodore Ts'o <tytso@....edu>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Dave Kleikamp <shaggy@...nel.org>,
        Ryusuke Konishi <konishi.ryusuke@...il.com>,
        "Konstantin Komarov" <almaz.alexandrovich@...agon-software.com>,
        Kees Cook <keescook@...omium.org>,
        Phillip Lougher <phillip@...ashfs.org.uk>,
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Subject: Re: don't use ->bd_inode to access the block device size

Hi Christoph,

> On 14 Oct 2021, at 07:28, Christoph Hellwig <hch@....de> wrote:
> 
> On Wed, Oct 13, 2021 at 07:10:13AM +0200, Christoph Hellwig wrote:
>> I wondered about adding a helper for looking at the size in byte units
>> to avoid the SECTOR_SHIFT shifts in various places.  But given that
>> I could not come up with a good name and block devices fundamentally
>> work in sector size granularity I decided against that.
> 
> So it seems like the biggest review feedback is that we should have
> such a helper.  I think the bdev_size name is the worst as size does
> not imply a particular unit.  bdev_nr_bytes is a little better but I'm
> not too happy.  Any other suggestions or strong opinions?

bdev_byte_size() would seem to address your concerns?

bdev_nr_bytes() would work though - it is analogous to bdev_nr_sectors() after all.

No strong opinion here but I do agree with you that bdev_size() is a bad choice for sure.  It is bound to cause bugs down the line when people forget what unit it is in.

Best regards,

	Anton
-- 
Anton Altaparmakov <anton at tuxera.com> (replace at with @)
Lead in File System Development, Tuxera Inc., http://www.tuxera.com/
Linux NTFS maintainer