On Fri, May 19, 2023 at 03:51:51PM +0100, Lorenzo Stoakes wrote: > Given you are sharply criticising the code I authored here, is it too much > to ask for you to cc- me, the author on commentaries like this? Thanks. > > On Fri, May 19, 2023 at 11:39:13AM +0200, Arnd Bergmann wrote: > > From: Arnd Bergmann <arnd@xxxxxxxx> > > > > While looking at an unused-variable warning, I noticed a new interface coming > > in that requires the use of IS_ERR_OR_NULL(), which tends to indicate bad > > interface design and is usually surprising to users. > > I am not sure I understand your reasoning, why does it 'tend to indicate > bad interface design'? You say that as if it is an obvious truth. Not > obvious to me at all. > > There are 3 possible outcomes from the function - an error, the function > failing to pin a page, or it succeeding in doing so. For some of the > callers that results in an error, for others it is not an error. No, there really isn't. Either it pins the page or it doesn't. Returning "NULL" to mean a specific kind of failure was encountered is crazy.. Especially if we don't document what that specific failure even was. IIRC if you look really closely the only time get_user_pages() actually returns 0 is if the input argument validation fails, which I think is a bug that should be fixed. get_user_pages() never returns 0, so get_user_page_vma_remote() never returns NULL. Until we get there collapsing the 0 to EIO is perfectly fine. Jason
