On Tue, Sep 19, 2023 at 12:01:59PM -0700, Axel Rasmussen wrote: > The example program doesn't depend on any extra features, so it does not > make use of the two-step feature handshake process. This is fine, but it > might set a bad example for programs which *do* depend on specific > features (e.g. they may conclude they don't need to do anything to > enable / detect them). > > No need to make the example program more complicated: let's just add a > comment indicating why we do it the way we do it in the example, and > describing briefly what a more complicated program would need to do > instead. > > The comment is kept rather brief; a full description of this feature > will be included in ioctl_userfaultfd.2 instead. > > Signed-off-by: Axel Rasmussen <axelrasmussen@xxxxxxxxxx> Reviewed-by: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> > --- > man2/userfaultfd.2 | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 > index 00d94e514..b2b79f61d 100644 > --- a/man2/userfaultfd.2 > +++ b/man2/userfaultfd.2 > @@ -881,6 +881,13 @@ main(int argc, char *argv[]) > if (uffd == \-1) > err(EXIT_FAILURE, "userfaultfd"); > \& > + /* NOTE: Two-step feature handshake is not needed here, since this > + example doesn't require any specific features. > + > + Programs that *do* should call UFFDIO_API twice: once with > + `features = 0` to detect features supported by this kernel, and > + again with the subset of features the program actually wants to > + enable. */ > uffdio_api.api = UFFD_API; > uffdio_api.features = 0; > if (ioctl(uffd, UFFDIO_API, &uffdio_api) == \-1) > -- > 2.42.0.459.ge4e396fd5e-goog > > -- Sincerely yours, Mike.
