On 11/10/2023 23:14, Eduard Zingerman wrote: > On Wed, 2023-10-11 at 23:05 +0100, Alan Maguire wrote: > [...] >>>>> I'm not sure I understand the logic behind "skip" features. >>>>> Take `decl_tag` for example: >>>>> - by default conf_load->skip_encoding_btf_decl_tag is 0; >>>>> - if `--btf_features=decl_tag` is passed it is still 0 because of the >>>>> `skip ? false : true` logic. >>>>> >>>>> If there is no way to change "skip" features why listing these at all? >>>>> >>>> You're right; in the case of a skip feature, I think we need the >>>> following behaviour >>>> >>>> 1. we skip the encoding by default (so the equivalent of >>>> --skip_encoding_btf_decl_tag, setting skip_encoding_btf_decl_tag >>>> to true >>>> >>>> 2. if the user however specifies the logical inversion of the skip >>>> feature in --btf_features (in this case "decl_tag" - or "all") >>>> skip_encoding_btf_decl_tag is set to false. >>>> >>>> So in my code we had 2 above but not 1. If both were in place I think >>>> we'd have the right set of behaviours. Does that sound right? >>> >>> You mean when --features=? is specified we default to >>> conf_load->skip_encoding_btf_decl_tag = true, and set it to false only >>> if "all" or "decl_tag" is listed in features, right? >>> >> >> Yep. Here's the comment I was thinking of adding for the next version, >> hopefully it clarifies this all a bit more than the original. >> >> +/* --btf_features=feature1[,feature2,..] allows us to specify >> + * a list of requested BTF features or "all" to enable all features. >> + * These are translated into the appropriate conf_load values via >> + * struct btf_feature which specifies the associated conf_load >> + * boolean field and whether its default (representing the feature being >> + * off) is false or true. >> + * >> + * btf_features is for opting _into_ features so for a case like >> + * conf_load->btf_gen_floats, the translation is simple; the presence >> + * of the "float" feature in --btf_features sets conf_load->btf_gen_floats >> + * to true. >> + * >> + * The more confusing case is for features that are enabled unless >> + * skipping them is specified; for example >> + * conf_load->skip_encoding_btf_type_tag. By default - to support >> + * the opt-in model of only enabling features the user asks for - >> + * conf_load->skip_encoding_btf_type_tag is set to true (meaning no >> + * type_tags) and it is only set to false if --btf_features contains >> + * the "type_tag" feature. >> + * >> + * So from the user perspective, all features specified via >> + * --btf_features are enabled, and if a feature is not specified, >> + * it is disabled. >> */ > > Sounds reasonable. Maybe also add a line saying that > skip_encoding_btf_decl_tag defaults to false if --btf_features is not > specified to remain backwards compatible? > good idea, will do! Thanks! Alan > Thanks, > Eduard > > [...]
