On 5.5.2010 23:49, James Bottomley wrote: > [Sam: I know you don't maintain kbuild anymore, but since you have the > most experience, if you could find time to comment, I'd be grateful] > > The select problem is that the kbuild select directive will turn a > symbol on without reference to its dependencies. This, in turn, means > that either selected symbols must select their dependencies, or that > people using select have to be aware of the selected symbol's dependency > and build those dependencies into their symbol (leading to duplication > and the possibility of getting the dependencies out of sync). We use > select for the scsi transport classes, so we run into this problem in > SCSI quite a lot. > > I think the correct fix is to make a symbol that selects another symbol > automatically inherit all of the selected symbol's dependencies. > > There seems to be a fairly easy way to do this in kbuild. Right at the > moment, select is handled as additional symbol values as the last point > in the symbol tree evaluation process. Instead, what I propose doing is > for every select symbol, we add an extra unconditional default for the > selected symbol of the selecting symbol's current value (this breaks a > possible dependency cycle) and add to the dependencies of the selecting > symbol, the symbol it's currently selecting. Nice trick :-). > There's one wrinkle to all of this in that the current parser for > default values stops when it finds the first valid (i.e. whose if clause > evaluates to true) default. To make the above scheme work, I need to > modify the default parser so it takes the highest tristate of all the > valid defaults (and bumps m to y for bool). We should check if some Kconfig file doesn't rely on this "first hit" behavior and fix it to explicitly list the condition for a given default. Another option would be to add default SYM1 || SYM2 to a symbol selected by SYM1 and SYM2. > Does this look acceptable to people? I think it should give the desired > result and has the added benefit that we can then strip the extra select > overlay out of the kbuild system (making the parser slightly simpler). > > If this looks like a good idea to people, I think I can code up a quick > patch. Other than the above, right now I don't see any issues with such approach. On a related note, I see Vegard's GSoC project to use a sat solver for kconfig got accepted [1]. Vegard, how is the project progressing? [1] http://socghop.appspot.com/gsoc/student_project/show/google/gsoc2010/psu_home/t127230762803 Michal -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
