linux-ext4 - Re: [PATCH v10 0/5] add support for direct I/O with fscrypt using blk-crypto

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Date:   Thu, 20 Jan 2022 00:30:23 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-fscrypt@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-xfs@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <david@...morbit.com>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Theodore Ts'o <tytso@....edu>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>
Subject: Re: [PATCH v10 0/5] add support for direct I/O with fscrypt using
 blk-crypto

On Wed, Jan 19, 2022 at 11:12:10PM -0800, Eric Biggers wrote:
> 
> Given the above, as far as I know the only remaining objection to this
> patchset would be that DIO constraints aren't sufficiently discoverable
> by userspace.  Now, to put this in context, this is a longstanding issue
> with all Linux filesystems, except XFS which has XFS_IOC_DIOINFO.  It's
> not specific to this feature, and it doesn't actually seem to be too
> important in practice; many other filesystem features place constraints
> on DIO, and f2fs even *only* allows fully FS block size aligned DIO.
> (And for better or worse, many systems using fscrypt already have
> out-of-tree patches that enable DIO support, and people don't seem to
> have trouble with the FS block size alignment requirement.)

It might make sense to use this as an opportunity to implement
XFS_IOC_DIOINFO for ext4 and f2fs.

> I plan to propose a new generic ioctl to address the issue of DIO
> constraints being insufficiently discoverable.  But until then, I'm
> wondering if people are willing to consider this patchset again, or
> whether it is considered blocked by this issue alone.  (And if this
> patchset is still unacceptable, would it be acceptable with f2fs support
> only, given that f2fs *already* only allows FS block size aligned DIO?)

I think the patchset looks fine, but I'd really love to have a way for
the alignment restrictions to be discoverable from the start.