Rasmus Villemoes <li...@rasmusvillemoes.dk> writes: > On 07/10/2019 21.26, Thomas Meyer wrote: >> commit b7b2562f7252 ("kernel/groups.c: use sort library function") >> introduced the sort library function. >> also use the bsearch library function instead of open-coding the binary >> search.
Hi, > Yes, but please note the difference between sorting the group_info and > searching it: The former is done quite rarely - the setgroups syscall is > used roughly once per login-session. > > But the searching of that structure is done more or less every time a > user accesses a file not owned by that user (e.g., any time a normal > user accesses anything in /usr) - at least if I'm reading > acl_permission_check() right. > > So using a callback-based interface, especially in a post-spectre world, > may have a somewhat large performance impact. okay, so the code is duplicated for performance reasons? nothing a compiler can inline, I guess. so what about a comment instead: diff --git a/kernel/groups.c b/kernel/groups.c index daae2f2dc6d4f..46b5d4cd53c2e 100644 --- a/kernel/groups.c +++ b/kernel/groups.c @@ -93,7 +93,7 @@ void groups_sort(struct group_info *group_info) } EXPORT_SYMBOL(groups_sort); -/* a simple bsearch */ +/* duplicate code from lib/bsearch.c for performance reasons */ int groups_search(const struct group_info *group_info, kgid_t grp) { unsigned int left, right; Mfg thomas