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

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Date:   Thu, 14 Oct 2021 08:13:59 -0500
From:   Dave Kleikamp <dave.kleikamp@...cle.com>
To:     Anton Altaparmakov <anton@...era.com>,
        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>,
        Josef Bacik <josef@...icpanda.com>,
        Theodore Ts'o <tytso@....edu>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        Ryusuke Konishi <konishi.ryusuke@...il.com>,
        Konstantin Komarov <almaz.alexandrovich@...agon-software.com>,
        Kees Cook <keescook@...omium.org>,
        Phillip Lougher <phillip@...ashfs.org.uk>,
        Jan Kara <jack@...e.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "drbd-dev@...ts.linbit.com" <drbd-dev@...ts.linbit.com>,
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        "ntfs3@...ts.linux.dev" <ntfs3@...ts.linux.dev>,
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Subject: Re: don't use ->bd_inode to access the block device size

On 10/14/21 4:32AM, Anton Altaparmakov wrote:
> 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.

I don't really mind bdev_size since it's analogous to i_size, but 
bdev_nr_bytes seems good to me.

Shaggy

> Best regards,
> 
> 	Anton
>