On 23 November 2011 22:03, Alexander Graf <ag...@suse.de> wrote: > On 23.11.2011, at 22:55, Peter Maydell <peter.mayd...@linaro.org> wrote: >> If the problem is that waitpid() can return success without writing to >> status, then this code is still not right because we will get the >> initial target waitstatus into status, and then pass it through >> host_to_target_waitstatus(), possibly modifying it, before writing >> it back to guest memory. > > Yes. Maybe we should add a check if input_state != output_state and > only then do the conversion?
I'm not sure this works (unless you go to the effort of implementing target_to_host_waitstatus() which seems overkill to me) but I'm not entirely sure what you're proposing to compare to what. >> I think waitpid() will always and only write to status if the return >> value is > 0 (ie it's a PID, not 0 or -1). So I think the right fix >> for this problem is to have the if() protecting the put_user_s32() >> read "if (ret && !is_error(ret) && ...". >> >> (ret == 0 is of course the WNOHANG-and-no-child-yet case you are hitting.) > > The man page wasn't really clear here. It sounded as if you can also > get 0 as return value and still have status change. That's why I > jumped through this hoop in the first place :) I think POSIX is clear enough. Either * a child status is available, return pid and write to status * WNOHANG & not ready, return 0 (don't write to status) * -1 and set errno (don't write to status) (strictly, whether status is written for EINTR is unpredictable, but I think we can assume nobody relies on this and I bet the kernel folks wouldn't worry too much about changing that between versions...) -- PMM
