From: Jakub Kicinski Date: Thu, 12 Dec 2024 04:13:29 +0000 (-0800) Subject: Merge branch 'lib-packing-introduce-and-use-un-pack_fields' X-Git-Tag: v6.14-rc1~162^2~238 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=91a91aacc5195982229265b02a021e670b3a034a;p=thirdparty%2Fkernel%2Fstable.git Merge branch 'lib-packing-introduce-and-use-un-pack_fields' Jacob Keller says: ==================== lib: packing: introduce and use (un)pack_fields 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. 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. This version now uses significantly improved macro checks, thanks to the work of Vladimir. We now only need 300 lines of macro for the generated checks. In addition, each new check only requires 4 lines of code for its macro implementation and 1 extra line in the CHECK_PACKED_FIELDS macro. This is significantly better than previous versions which required ~2700 lines. The CHECK_PACKED_FIELDS macro uses __builtin_choose_expr to select the appropriately sized CHECK_PACKED_FIELDS_N macro. This enables directly adding CHECK_PACKED_FIELDS calls into the pack_fields and unpack_fields macros. Drivers no longer need to call the CHECK_PACKED_FIELDS_N macros directly, and we do not need to modify Kbuild or introduce multiple CONFIG options. The code for the CHECK_PACKED_FIELDS_(0..50) and CHECK_PACKED_FIELDS itself can be generated from the C program in scripts/gen_packed_field_checks.c. This little C program may be used in the future to update the checks to more sizes if a driver with more than 50 fields appears in the future. The total amount of required code is now much smaller, and we don't anticipate needing to increase the size very often. Thus, it makes sense to simply commit the result directly instead of attempting to modify Kbuild to automatically generate it. This version uses the 5-argument format of pack_fields and unpack_fields, with the size of the packed buffer passed as one of the arguments. We do enforce that the compiler can tell its a constant using __builtin_constant_p(), ensuring that the size checks are handled at compile time. We could reduce these to 4 arguments and require that the passed in pbuf be of a type which has the appropriate size. I opted against that because it makes the API less flexible and a bit less natural to use in existing code. Signed-off-by: Jacob Keller Reviewed-by: Vladimir Oltean v9: https://lore.kernel.org/20241204-packing-pack-fields-and-ice-implementation-v9-0-81c8f2bd7323@intel.com v8: https://lore.kernel.org/20241203-packing-pack-fields-and-ice-implementation-v8-0-2ed68edfe583@intel.com v7: https://lore.kernel.org/20241202-packing-pack-fields-and-ice-implementation-v7-0-ed22e38e6c65@intel.com v6: https://lore.kernel.org/20241118-packing-pack-fields-and-ice-implementation-v6-0-6af8b658a6c3@intel.com v5: https://lore.kernel.org/20241111-packing-pack-fields-and-ice-implementation-v5-0-80c07349e6b7@intel.com v4: https://lore.kernel.org/20241108-packing-pack-fields-and-ice-implementation-v4-0-81a9f42c30e5@intel.com v3: https://lore.kernel.org/20241107-packing-pack-fields-and-ice-implementation-v3-0-27c566ac2436@intel.com v2: https://lore.kernel.org/20241025-packing-pack-fields-and-ice-implementation-v2-0-734776c88e40@intel.com v1: https://lore.kernel.org/20241011-packing-pack-fields-and-ice-implementation-v1-0-d9b1f7500740@intel.com ==================== Link: https://patch.msgid.link/20241210-packing-pack-fields-and-ice-implementation-v10-0-ee56a47479ac@intel.com Signed-off-by: Jakub Kicinski --- 91a91aacc5195982229265b02a021e670b3a034a