On Jun 11, 2019, at 2:48 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, 12 Jun 2019 01:08:36 +0530 Shyam Saini <shyam.saini@xxxxxxxxxxxxxxxxxxxx> wrote: > >> Currently, there are 3 different macros, namely sizeof_field, SIZEOF_FIELD >> and FIELD_SIZEOF which are used to calculate the size of a member of >> structure, so to bring uniformity in entire kernel source tree lets use >> FIELD_SIZEOF and replace all occurrences of other two macros with this. >> >> For this purpose, redefine FIELD_SIZEOF in include/linux/stddef.h and >> tools/testing/selftests/bpf/bpf_util.h and remove its defination from >> include/linux/kernel.h >> >> In favour of FIELD_SIZEOF, this patch also deprecates other two similar >> macros sizeof_field and SIZEOF_FIELD. >> >> For code compatibility reason, retain sizeof_field macro as a wrapper macro >> to FIELD_SIZEOF > > As Alexey has pointed out, C structs and unions don't have fields - > they have members. So this is an opportunity to switch everything to > a new member_sizeof(). > > What do people think of that and how does this impact the patch footprint? I did a check, and FIELD_SIZEOF() is used about 350x, while sizeof_field() is about 30x, and SIZEOF_FIELD() is only about 5x. That said, I'm much more in favour of "sizeof_field()" or "sizeof_member()" than FIELD_SIZEOF(). Not only does that better match "offsetof()", with which it is closely related, but is also closer to the original "sizeof()". Since this is a rather trivial change, it can be split into a number of patches to get approval/landing via subsystem maintainers, and there is no huge urgency to remove the original macros until the users are gone. It would make sense to remove SIZEOF_FIELD() and sizeof_field() quickly so they don't gain more users, and the remaining FIELD_SIZEOF() users can be whittled away as the patches come through the maintainer trees. Cheers, Andreas
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