On Mon, Sep 01, 2025 at 05:21:22PM +0200, "Gustavo A. R. Silva" <gust...@embeddedor.com> wrote: > Because struct cgroup ends in a flexible-array member `ancestors`. > This triggers the -Wflex-array-member-not-at-end warns about. So, > while `ancestors` is indeed a flexible array, any instance of > cgroup embedded in another struct should be placed at the end.
Oh, so TRAILING_OVERLAP() won't work like that? (I thought that it'd hide the FAM from the end of the union and thus it could embedded when wrapped like this. On second thought, I realize that's exclusive with the static validations.) > However, if we change it to something like this (and of course > updating any related code, accordingly): > > - struct cgroup *ancestors[]; > + struct cgroup **ancestors; > > Then the flex in the middle issue goes away, and we can have > struct cgroup embedded in another struct anywhere. > > The question is if this would be an acceptable solution? > > I'd probably prefer this to remain a flexible-array member, > but I'd like to hear people's opinions and feedback. :) I'd prefer if cgroup_create could still work with one allocation only both for struct cgroup and its ancestors array. (Cgroup allocation happens many times in a day.) The increase in struct cgroup_root size is IMO not that problematic. (There are typically at most CGROUP_SUBSYS_COUNT roots with gradual trend to only the single cgrp_dfl_root.) Note that it'd be good to keep it enclosed within struct cgroup_root (cgroup1_root_to_use could use struct_size()), however, the cgrp_dfl_root would still need the storage somewhere. HTH, Michal
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