[RFC PATCH v2 0/7] make statx() return I/O alignment information

Eric Biggers
2022-05-18T23:53:35Z

This patchset makes the statx() system call return I/O alignment
information, roughly following the design that was suggested at
https://lore.kernel.org/linux-fsdevel/20220120071215.123274-1-ebiggers@kernel.org/T/#u

This feature solves two problems: (a) it allows userspace to determine
when a file supports direct I/O, and with what alignment restrictions;
and (b) it allows userspace to determine the optimum I/O alignment for a
file. For more details, see patch 1.

This is an RFC. I'd greatly appreciate any feedback on the UAPI, as
that obviously needs to be gotten right from the beginning. E.g., does
the proposed set of fields make sense? Am I including the right
information in stx_offset_align_optimal?

Patch 1 adds the VFS support for STATX_IOALIGN. The remaining patches
wire it up to ext4 and f2fs. Support for other filesystems can be added
later. We could also support this on block device files; however, since
block device nodes have different inodes from the block devices
themselves, it wouldn't apply to statx("/dev/$foo") but rather just to
'fd = open("/dev/foo"); statx(fd)'. I'm unsure how useful that would be.

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 5) 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 v5.18-rc7.

No changes since v1, which I sent a few months ago; I'm resending this
because people seem interested in it again
(https://lore.kernel.org/r/20220518171131.3525293-1-kbusch@fb.com).

Eric Biggers (7):
statx: add I/O alignment information
fscrypt: change fscrypt_dio_supported() to prepare for STATX_IOALIGN
ext4: support STATX_IOALIGN
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_IOALIGN

fs/crypto/inline_crypt.c | 48 +++++++++++++++---------------
fs/ext4/ext4.h | 1 +
fs/ext4/file.c | 10 +++----
fs/ext4/inode.c | 31 ++++++++++++++++++++
fs/f2fs/f2fs.h | 45 -----------------------------
fs/f2fs/file.c | 61 ++++++++++++++++++++++++++++++++++++++-
fs/stat.c | 3 ++
include/linux/fscrypt.h | 7 ++---
include/linux/stat.h | 3 ++
include/uapi/linux/stat.h | 9 ++++--
10 files changed, 136 insertions(+), 82 deletions(-)

base-commit: 42226c989789d8da4af1de0c31070c96726d990c
--
2.36.1