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Vladimir Oltean a636ba5e86 lib: packing: adjust definitions and implementation for arbitrary buffer lengths
Jacob Keller has a use case for packing() in the intel/ice networking
driver, but it cannot be used as-is.

Simply put, the API quirks for LSW32_IS_FIRST and LITTLE_ENDIAN are
naively implemented with the undocumented assumption that the buffer
length must be a multiple of 4. All calculations of group offsets and
offsets of bytes within groups assume that this is the case. But in the
ice case, this does not hold true. For example, packing into a buffer
of 22 bytes would yield wrong results, but pretending it was a 24 byte
buffer would work.

Rather than requiring such hacks, and leaving a big question mark when
it comes to discontinuities in the accessible bit fields of such buffer,
we should extend the packing API to support this use case.

It turns out that we can keep the design in terms of groups of 4 bytes,
but also make it work if the total length is not a multiple of 4.
Just like before, imagine the buffer as a big number, and its most
significant bytes (the ones that would make up to a multiple of 4) are
missing. Thus, with a big endian (no quirks) interpretation of the
buffer, those most significant bytes would be absent from the beginning
of the buffer, and with a LSW32_IS_FIRST interpretation, they would be
absent from the end of the buffer. The LITTLE_ENDIAN quirk, in the
packing() API world, only affects byte ordering within groups of 4.
Thus, it does not change which bytes are missing. Only the significance
of the remaining bytes within the (smaller) group.

No change intended for buffer sizes which are multiples of 4. Tested
with the sja1105 driver and with downstream unit tests.

Link: https://lore.kernel.org/netdev/a0338310-e66c-497c-bc1f-a597e50aa3ff@intel.com/
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Tested-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://patch.msgid.link/20241002-packing-kunit-tests-and-split-pack-unpack-v2-2-8373e551eae3@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2024-10-03 15:32:03 -07:00
arch move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
block move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
Documentation lib: packing: adjust definitions and implementation for arbitrary buffer lengths 2024-10-03 15:32:03 -07:00
drivers Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-10-03 10:05:55 -07:00
fs three small ksmbd server fixes 2024-10-03 09:38:16 -07:00
include Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-10-03 10:05:55 -07:00
init Rust changes for v6.12 2024-09-25 10:25:40 -07:00
io_uring for-6.12/io_uring-20240922 2024-09-24 11:11:38 -07:00
ipc struct fd layout change (and conversion to accessor helpers) 2024-09-23 09:35:36 -07:00
kernel Getting rid of asm/unaligned.h includes 2024-10-02 16:42:28 -07:00
lib lib: packing: adjust definitions and implementation for arbitrary buffer lengths 2024-10-03 15:32:03 -07:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm 19 hotfixes. 13 are cc:stable. 2024-09-27 10:27:22 -07:00
net Including fixes from ieee802154, bluetooth and netfilter. 2024-10-03 09:44:00 -07:00
rust Rust changes for v6.12 2024-09-25 10:25:40 -07:00
samples [tree-wide] finally take no_llseek out 2024-09-27 08:18:43 -07:00
scripts Reduce Coccinelle choices in string_choices.cocci 2024-09-28 21:33:11 +02:00
security move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
sound move asm/unaligned.h to linux/unaligned.h 2024-10-02 17:23:23 -04:00
tools Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2024-10-03 10:05:55 -07:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt x86: 2024-09-28 09:20:14 -07:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Kbuild updates for v6.12 2024-09-24 13:02:06 -07:00
.mailmap Summary 2024-09-24 11:08:40 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Mark powerpc spufs as orphaned 2024-08-19 21:27:56 +10:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Modules changes for v6.12-rc1 2024-09-28 09:06:15 -07:00
Makefile Linux 6.12-rc1 2024-09-29 15:06:19 -07:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

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 reStructuredText 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.