Richard, On 04/01/2014 08:25 PM, Richard Hansen wrote: > For the flags parameter, POSIX says "Either MS_ASYNC or MS_SYNC shall > be specified, but not both." [1] There was already a test for the > "both" condition. Add a test to ensure that the caller specified one > of the flags; fail with EINVAL if neither are specified. > > Without this change, specifying neither is the same as specifying > flags=MS_ASYNC because nothing in msync() is conditioned on the > MS_ASYNC flag. This has not always been true,
I am curious (since such things should be documented)--when was it not true? > and there's no good > reason to believe that this behavior would have persisted > indefinitely. > > The msync(2) man page (as currently written in man-pages.git) is > silent on the behavior if both flags are unset, so this change should > not break an application written by somone who carefully reads the > Linux man pages or the POSIX spec. Sadly, people do not always carefully read man pages, so there remains the chance that a change like this will break applications. Aside from standards conformance, what do you see as the benefit of the change? Thanks, Michael > [1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/msync.html > > Signed-off-by: Richard Hansen <rhan...@bbn.com> > Reported-by: Greg Troxel <g...@ir.bbn.com> > Reviewed-by: Greg Troxel <g...@ir.bbn.com> > --- > > This is a resend of: > http://article.gmane.org/gmane.linux.kernel/1554416 > I didn't get any feedback from that submission, so I'm resending it > without changes. > > mm/msync.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/msync.c b/mm/msync.c > index 632df45..472ad3e 100644 > --- a/mm/msync.c > +++ b/mm/msync.c > @@ -42,6 +42,8 @@ SYSCALL_DEFINE3(msync, unsigned long, start, size_t, > len, int, flags) > goto out; > if ((flags & MS_ASYNC) && (flags & MS_SYNC)) > goto out; > + if (!(flags & (MS_ASYNC | MS_SYNC))) > + goto out; > error = -ENOMEM; > len = (len + ~PAGE_MASK) & PAGE_MASK; > end = start + len; > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
