Messages in this thread | | | From | Bill Wendling <> | Date | Tue, 27 Jul 2021 13:22:21 -0700 | Subject | Re: [PATCH v2 1/3] base: mark 'no_warn' as unused |
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On Tue, Jul 27, 2021 at 1:17 PM Segher Boessenkool <segher@kernel.crashing.org> wrote: > > On Tue, Jul 27, 2021 at 07:59:24PM +0200, Greg Kroah-Hartman wrote: > > On Tue, Jul 27, 2021 at 10:39:49AM -0700, Nick Desaulniers wrote: > > > I think warn_unused_result should only really be used for functions > > > where the return value should be used 100% of the time. > > > > I too want a shiny new pony. > > > > But here in the real world, sometimes you have functions that for 99% of > > the users, you do want them to check the return value, but when you use > > them in core code or startup code, you "know" you are safe to ignore the > > return value. > > > > That is the case here. We have other fun examples of where people have > > tried to add error handling to code that runs at boot that have actually > > introduced security errors and they justify it with "but you have to > > check error values!" > > > > > If there are > > > cases where it's ok to not check the return value, consider not using > > > warn_unused_result on function declarations. > > > > Ok, so what do you do when you have a function like this where 99.9% of > > the users need to check this? Do I really need to write a wrapper > > function just for it so that I can use it "safely" in the core code > > instead? > > > > Something like: > > > > void do_safe_thing_and_ignore_the_world(...) > > { > > __unused int error; > > > > error = do_thing(...); > > } > > > > Or something else to get the compiler to be quiet about error being set > > and never used? > > The simplest is to write > if (do_thing()) { > /* Nothing here, we can safely ignore the return value > * here, because of X and Y and I don't know, I have no > * idea actually why we can in this example. Hopefully > * in real code people do have a good reason :-) > */ > } > > which should work in *any* compiler, doesn't need any extension, is > quite elegant, and encourages documenting why we ignore the return > value here. > Or better still, use sysfs_create_link_nowarn() instead of sysfs_create_link(). We'll just have to take the "__must_check" attribute off the sysfs_create_link_nowarn() declaration.
-bw
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