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Eric Biggers 825cf206ed statx: add direct I/O alignment information 
Traditionally, the conditions for when DIO (direct I/O) is supported
were fairly simple.  For both block devices and regular files, DIO had
to be aligned to the logical block size of the block device.

However, due to filesystem features that have been added over time (e.g.
multi-device support, data journalling, inline data, encryption, verity,
compression, checkpoint disabling, log-structured mode), the conditions
for when DIO is allowed on a regular file have gotten increasingly
complex.  Whether a particular regular file supports DIO, and with what
alignment, can depend on various file attributes and filesystem mount
options, as well as which block device(s) the file's data is located on.

Moreover, the general rule of DIO needing to be aligned to the block
device's logical block size was recently relaxed to allow user buffers
(but not file offsets) aligned to the DMA alignment instead.  See
commit bf8d08532b ("iomap: add support for dma aligned direct-io").

XFS has an ioctl XFS_IOC_DIOINFO that exposes DIO alignment information.
Uplifting this to the VFS is one possibility.  However, as discussed
(https://lore.kernel.org/linux-fsdevel/20220120071215.123274-1-ebiggers@kernel.org/T/#u),
this ioctl is rarely used and not known to be used outside of
XFS-specific code.  It was also never intended to indicate when a file
doesn't support DIO at all, nor was it intended for block devices.

Therefore, let's expose this information via statx().  Add the
STATX_DIOALIGN flag and two new statx fields associated with it:

* stx_dio_mem_align: the alignment (in bytes) required for user memory
  buffers for DIO, or 0 if DIO is not supported on the file.

* stx_dio_offset_align: the alignment (in bytes) required for file
  offsets and I/O segment lengths for DIO, or 0 if DIO is not supported
  on the file.  This will only be nonzero if stx_dio_mem_align is
  nonzero, and vice versa.

Note that as with other statx() extensions, if STATX_DIOALIGN isn't set
in the returned statx struct, then these new fields won't be filled in.
This will happen if the file is neither a regular file nor a block
device, or if the file is a regular file and the filesystem doesn't
support STATX_DIOALIGN.  It might also happen if the caller didn't
include STATX_DIOALIGN in the request mask, since statx() isn't required
to return unrequested information.

This commit only adds the VFS-level plumbing for STATX_DIOALIGN.  For
regular files, individual filesystems will still need to add code to
support it.  For block devices, a separate commit will wire it up too.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20220827065851.135710-2-ebiggers@kernel.org
2022-09-11 19:47:04 -05:00
arch Misc irqchip fixes: LoongArch driver fixes and a Hyper-V IOMMU fix. 2022-08-21 15:09:55 -07:00
block block-6.0-2022-08-19 2022-08-20 10:17:05 -07:00
certs Kbuild updates for v5.20 2022-08-10 10:40:41 -07:00
crypto crypto: blake2b: effectively disable frame size warning 2022-08-10 17:59:11 -07:00
Documentation asm goto: eradicate CC_HAS_ASM_GOTO 2022-08-21 10:06:28 -07:00
drivers Misc irqchip fixes: LoongArch driver fixes and a Hyper-V IOMMU fix. 2022-08-21 15:09:55 -07:00
fs statx: add direct I/O alignment information 2022-09-11 19:47:04 -05:00
include statx: add direct I/O alignment information 2022-09-11 19:47:04 -05:00
init asm goto: eradicate CC_HAS_ASM_GOTO 2022-08-21 10:06:28 -07:00
io_uring io_uring/net: use right helpers for async_data 2022-08-18 07:27:20 -06:00
ipc Updates to various subsystems which I help look after. lib, ocfs2, 2022-08-07 10:03:24 -07:00
kernel Various fixes for tracing: 2022-08-21 14:49:42 -07:00
lib lib/cpumask: drop always-true preprocessor guard 2022-08-15 11:00:44 -07:00
LICENSES LICENSES/LGPL-2.1: Add LGPL-2.1-or-later as valid identifiers 2021-12-16 14:33:10 +01:00
mm - hugetlb_vmemmap cleanups from Muchun Song 2022-08-10 11:18:00 -07:00
net tcp: handle pure FIN case correctly 2022-08-18 11:04:56 -07:00
samples Tracing updates for 5.20 / 6.0 2022-08-05 09:41:12 -07:00
scripts asm goto: eradicate CC_HAS_ASM_GOTO 2022-08-21 10:06:28 -07:00
security hardening fixes for v6.0-rc2 2022-08-19 13:56:14 -07:00
sound sound fixes for 6.0-rc2 2022-08-19 09:46:11 -07:00
tools asm goto: eradicate CC_HAS_ASM_GOTO 2022-08-21 10:06:28 -07:00
usr Not a lot of material this cycle. Many singleton patches against various 2022-05-27 11:22:03 -07:00
virt KVM: Drop unnecessary initialization of "ops" in kvm_ioctl_create_device() 2022-08-19 04:05:43 -04:00
.clang-format PCI/DOE: Add DOE mailbox support functions 2022-07-19 15:38:04 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore kbuild: split the second line of *.mod into *.usyms 2022-05-08 03:16:59 +09:00
.mailmap Updates to various subsystems which I help look after. lib, ocfs2, 2022-08-07 10:03:24 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS drm for 5.20/6.0 2022-08-03 19:52:08 -07:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS 5 cifs/smb3 fixes, one for stable 2022-08-21 10:21:16 -07:00
Makefile Linux 6.0-rc2 2022-08-21 17:32:54 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.