On Mon, Mar 22, 2010 at 11:55:08AM +0000, Al Viro wrote: > On Mon, Mar 22, 2010 at 04:39:37PM +1100, Nick Piggin wrote: > > It's ugly and lazy that we do these default aops in case it has not > > been filled in by the filesystem. > > > > A NULL operation should always mean either: we don't support the > > operation; we don't require any action; or a bug in the filesystem, > > depending on the context. > > > > In practice, if we get rid of these fallbacks, it will be clearer > > what operations are used by a given address_space_operations struct, > > reduce branches, reduce #if BLOCK ifdefs, and should allow us to get > > rid of all the buffer_head knowledge from core mm and fs code. > > > > We could add a patch like this which spits out a recipe for how to fix > > up filesystems and get them all converted quite easily. > > Um. Seeing that part of that is for methods absent in mainline (->release(), > ->sync()), I'd say that making it mandatory at that point is a bad idea. Yea I didn't have patch order right for a real submission. And clearly _most_ of the in-tree fses should be converted before actually merging such warnings. > > As for the rest... We have 90 instances of address_space_operations > in the kernel. Out of those: > 28 have ->releasepage != NULL > 27 have ->set_page_dirty != NULL > 25 have ->invalidatepage != NULL > > So I'm not even sure that adding that much boilerplate makes sense. Fair position. The arguments pro are more about cleaner code than any major improvement. Main thing I don't like that it isn't trivial to see whether an address space class will use a given function or not. You'd have to first check the aop to find it's NULL, then check callers to see whether there is a fallback, then check the fs in case it can attach buffers that will still be attached at point of calls. I personally would prefer function pointers filled in. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>