On Thu, 2010-05-06 at 16:24 +0200, Michal Marek wrote: > 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. I actually asked kconfig to generate the list of symbols (in my config) with multiple defaults. It's pretty small and the default y seems to be the thing with multiple if clauses, so they act like or statements. The list is USB_ARCH_HAS_HCD has 4 defaults DEFCONFIG_LIST has 5 defaults MAC80211_RC_DEFAULT has 2 defaults X86_L1_CACHE_SHIFT has 2 defaults SPLIT_PTLOCK_CPUS has 2 defaults X86_MINIMUM_CPU_FAMILY has 3 defaults DEFAULT_TCP_CONG has 2 defaults DEFCONFIG_LIST has 5 defaults USB_ARCH_HAS_HCD has 4 defaults X86_L1_CACHE_SHIFT has 2 defaults X86_MINIMUM_CPU_FAMILY has 3 defaults SPLIT_PTLOCK_CPUS has 2 defaults DEFAULT_TCP_CONG has 2 defaults MAC80211_RC_DEFAULT has 2 defaults > Another option would be to add > default SYM1 || SYM2 > to a symbol selected by SYM1 and SYM2. Well, that's effectively what the proposal does (it or's the states). > > 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 James -- 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
