linux-ext4 - Re: [PATCH v9 5/9] block: Make bio_iov_iter_get_pages() respect bio_required_sector

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Date:   Sat, 24 Jul 2021 08:19:15 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Satya Tangirala <satyat@...gle.com>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        Jens Axboe <axboe@...nel.dk>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-kernel@...r.kernel.org, linux-fscrypt@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, linux-xfs@...r.kernel.org,
        linux-block@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v9 5/9] block: Make bio_iov_iter_get_pages() respect
 bio_required_sector_alignment()

On Fri, Jul 23, 2021 at 02:33:02PM -0700, Eric Biggers wrote:
> I do still wonder if we should just not support that...  Dave is the only person
> who has asked for it, and it's a lot of trouble to support.
> 
> I also noticed that f2fs has always only supported direct I/O that is *fully*
> fs-block aligned (including the I/O segments) anyway.  So presumably that
> limitation is not really that important after all...
> 
> Does anyone else have thoughts on this?

There are some use cases that really like sector aligned direct I/O,
what comes to mind is some data bases, and file system repair tools
(the latter on the raw block device).  So it is nice to support, but not
really required.

So for now I'd much prefer to initially support inline encryption for
direct I/O without that if that simplifies the support.  We can revisit
the additional complexity later.

Also note that for cheap flash media pretending support for 512 byte
blocks is actually a bit awwkward, so just presenting the media as
having 4096 sectors in these setups would be the better choice anyway.