On Fri, Oct 13, 2017 at 1:44 AM, Michael Lyle <mlyle@xxxxxxxx> wrote: > On 10/12/2017 07:37 AM, Liang Chen wrote: >> The use of the union reduces the size of closure struct by taking advantage >> of the current size of its members. The offset of func in work_struct equals >> the size of the first three members, so that work.work_func will just >> reference the forth member - fn. >> >> This is smart but dangerous. It can be broken if work_struct or the other >> structs get changed, and can be a bit difficult to debug. >> >> Signed-off-by: Liang Chen <liangchen.linux@xxxxxxxxx> > > So the objective here is to make sure that struct work_struct and the > anonymous struct remain identical? I agree that's a potential problem > for future maintenance. > > Could we use BUILD_BUG_ON with offsets and sizes to do the same, to get > compile-time checking and avoid doing anything at runtime (I know the > compiler can usually omit the BUG but better to be safe)? Otherwise a > kernel that triggered this problem would compile, and it'd only be if > someone actually used bcache that it would trigger. > > Mike Yeah, the objective here is to make sure the offset of func and fn remains the same so cl->work.func will just reference cl->fn. Sure, BUILD_BUG_ON will do the work, and can capture the problem at compile time. Thanks for the reminding! I will submit another patch soon. Thanks, Liang -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
