Re: [PATCH v4 0/9] make statx() return DIO alignment information

Eric Biggers
2022-08-27T07:08:10Z

On Fri, Aug 26, 2022 at 01:19:37PM -0400, Jeff Layton wrote:
> On Fri, 2022-07-22 at 00:12 -0700, Eric Biggers wrote:
> > This patchset makes the statx() system call return direct I/O (DIO)
> > alignment information. This allows userspace to easily determine
> > whether a file supports DIO, and if so with what alignment restrictions.
> >
> > Patch 1 adds the basic VFS support for STATX_DIOALIGN. Patch 2 wires it
> > up for all block device files. The remaining patches wire it up for
> > regular files on ext4, f2fs, and xfs. Support for regular files on
> > other filesystems can be added later.
> >
> > I've also written a man-pages patch, which I'm sending separately.
> >
> > Note, f2fs has one corner case where DIO reads are allowed but not DIO
> > writes. The proposed statx fields can't represent this. My proposal
> > (patch 6) is to just eliminate this case, as it seems much too weird.
> > But I'd appreciate any feedback on that part.
> >
> > This patchset applies to v5.19-rc7.
> >
> > Changed v3 => v4:
> > - Added xfs support.
> >
> > - Moved the helper function for block devices into block/bdev.c.
> >
> > - Adjusted the ext4 patch to not introduce a bug where misaligned DIO
> > starts being allowed on encrypted files when it gets combined with
> > the patch "iomap: add support for dma aligned direct-io" that is
> > queued in the block tree for 5.20.
> >
> > - Made a simplification in fscrypt_dio_supported().
> >
> > Changed v2 => v3:
> > - Dropped the stx_offset_align_optimal field, since its purpose
> > wasn't clearly distinguished from the existing stx_blksize.
> >
> > - Renamed STATX_IOALIGN to STATX_DIOALIGN, to reflect the new focus
> > on DIO only.
> >
> > - Similarly, renamed stx_{mem,offset}_align_dio to
> > stx_dio_{mem,offset}_align, to reflect the new focus on DIO only.
> >
> > - Wired up STATX_DIOALIGN on block device files.
> >
> > Changed v1 => v2:
> > - No changes.
> >
> > Eric Biggers (9):
> > statx: add direct I/O alignment information
> > vfs: support STATX_DIOALIGN on block devices
> > fscrypt: change fscrypt_dio_supported() to prepare for STATX_DIOALIGN
> > ext4: support STATX_DIOALIGN
> > f2fs: move f2fs_force_buffered_io() into file.c
> > f2fs: don't allow DIO reads but not DIO writes
> > f2fs: simplify f2fs_force_buffered_io()
> > f2fs: support STATX_DIOALIGN
> > xfs: support STATX_DIOALIGN
> >
> > block/bdev.c | 25 ++++++++++++++++++++
> > fs/crypto/inline_crypt.c | 49 +++++++++++++++++++--------------------
> > fs/ext4/ext4.h | 1 +
> > fs/ext4/file.c | 37 ++++++++++++++++++++---------
> > fs/ext4/inode.c | 36 ++++++++++++++++++++++++++++
> > fs/f2fs/f2fs.h | 45 -----------------------------------
> > fs/f2fs/file.c | 45 ++++++++++++++++++++++++++++++++++-
> > fs/stat.c | 14 +++++++++++
> > fs/xfs/xfs_iops.c | 9 +++++++
> > include/linux/blkdev.h | 4 ++++
> > include/linux/fscrypt.h | 7 ++----
> > include/linux/stat.h | 2 ++
> > include/uapi/linux/stat.h | 4 +++-
> > 13 files changed, 190 insertions(+), 88 deletions(-)
> >
> > base-commit: ff6992735ade75aae3e35d16b17da1008d753d28
>
> Hi Eric,
>
> Can I ask what your plans are with this set? I didn't see it in
> linux-next yet, so I wasn't sure when you were looking to get it merged.
> I'm working on patches to add a new statx field for the i_version
> counter as well and I want to make sure that our work doesn't collide.
>

I've just sent v5. I guess I'll try to get it merged for 6.1. We were a bit
stuck on the read-only DIO issue. All things considered though, including that
Christoph thinks it's possible for f2fs to support DIO writes on zoned block
devices, I'm willing to bet that read-only DIO doesn't really matter enough for
it to be worth it to add a direction field to STATX_DIOALIGN (which would make
it harder to use STATX_DIOALIGN, as the field would always have to be checked).

- Eric