[PATCH net-next 0/8] lib: packing: introduce and use (un)pack_fields

Jacob Keller
2024-10-11T18:50:07Z

This series improves the packing library with a new API for packing or
unpacking a large number of fields at once with minimal code footprint. The
API is then used to replace bespoke packing logic in the ice driver,
preparing it to handle unpacking in the future. Finally, the ice driver has
a few other cleanups related to the packing logic.

The pack_fields and unpack_fields functions have the following improvements
over the existing pack() and unpack() API:

1. Packing or unpacking a large number of fields takes significantly less
code. This significantly reduces the .text size for an increase in the
.data size which is much smaller.

2. The unpacked data can be stored in sizes smaller than u64 variables.
This reduces the storage requirement both for runtime data structures,
and for the rodata defining the fields. This scales with the number of
fields used.

3. Most of the error checking is done at compile time, rather than
runtime via CHECK_PACKED_FIELD_* macros. This saves wasted computation
time, *and* catches errors in the field definitions immediately instead
of only after the offending code executes.

The actual packing and unpacking code still uses the u64 size
variables. However, these are converted to the appropriate field sizes when
storing or reading the data from the buffer.

One complexity is that the CHECK_PACKED_FIELD_* macros need to be defined
one per size of the packed_fields array. This is because we don't have a
good way to handle the ordering checks otherwise. The C pre-processor is
unable to generate and run variable length loops at compile time.

This is a significant amount of macro code, ~22,000 lines of code. To
ensure it is correct and to avoid needing to store this directly in the
kernel history, this file is generated as <generated/packing-checks.h> via
a small C program, gen_packing_checks. To generate this, we need to update
the top level Kbuild process to include the compilation of
gen_packing_checks and execution to generate the packing-checks.h file.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
---
Jacob Keller (5):
ice: remove int_q_state from ice_tlan_ctx
ice: use <linux/packing.h> for Tx and Rx queue context data
ice: reduce size of queue context fields
ice: move prefetch enable to ice_setup_rx_ctx
ice: cleanup Rx queue context programming functions

Vladimir Oltean (3):
lib: packing: create __pack() and __unpack() variants without error checking
lib: packing: demote truncation error in pack() to a warning in __pack()
lib: packing: add pack_fields() and unpack_fields()

drivers/net/ethernet/intel/ice/ice_common.h | 12 +-
drivers/net/ethernet/intel/ice/ice_lan_tx_rx.h | 49 +---
include/linux/packing.h | 69 ++++++
drivers/net/dsa/sja1105/sja1105_static_config.c | 8 +-
drivers/net/ethernet/intel/ice/ice_base.c | 6 +-
drivers/net/ethernet/intel/ice/ice_common.c | 300 +++++-------------------
lib/gen_packing_checks.c | 31 +++
lib/packing.c | 285 ++++++++++++++++------
Kbuild | 13 +-
drivers/net/ethernet/intel/Kconfig | 1 +
10 files changed, 423 insertions(+), 351 deletions(-)
---
base-commit: d677aebd663ddc287f2b2bda098474694a0ca875
change-id: 20241004-packing-pack-fields-and-ice-implementation-b17c7ce8e373

Best regards,
--
Jacob Keller <jacob.e.keller@intel.com>