Re: [f2fs-dev] [PATCH v10 0/5] add support for direct I/O with fscrypt using blk-crypto

[Christoph Hellwig <hch@infradead.org>]

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.


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