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.li...@gmail.com>
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
