On Mon, Oct 09, 2017 at 03:45:51PM -0700, Prakash Sangappa wrote: > Userfaultfd feature UFFD_FEATURE_SIGBUS was merged recently and should > be available in Linux 4.14 release. This patch is for the manpage > changes documenting this API. > > Documents the following commit: > > commit 2d6d6f5a09a96cc1fec7ed992b825e05f64cb50e > Author: Prakash Sangappa <prakash.sanga...@oracle.com> > Date: Wed Sep 6 16:23:39 2017 -0700 > > mm: userfaultfd: add feature to request for a signal delivery > > Signed-off-by: Prakash Sangappa <prakash.sanga...@oracle.com>
Reviewed-by: Mike Rapoport <r...@linux.vnet.ibm.com> > --- > v2: Incorporated review feedback changes. > --- > man2/ioctl_userfaultfd.2 | 9 +++++++++ > man2/userfaultfd.2 | 23 +++++++++++++++++++++++ > 2 files changed, 32 insertions(+) > > diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2 > index 60fd29b..32f0744 100644 > --- a/man2/ioctl_userfaultfd.2 > +++ b/man2/ioctl_userfaultfd.2 > @@ -196,6 +196,15 @@ with the > flag set, > .BR memfd_create (2), > and so on. > +.TP > +.B UFFD_FEATURE_SIGBUS > +Since Linux 4.14, If this feature bit is set, no page-fault events > +.B (UFFD_EVENT_PAGEFAULT) > +will be delivered, instead a > +.B SIGBUS > +signal will be sent to the faulting process. Applications using this > +feature will not require the use of a userfaultfd monitor for processing > +memory accesses to the regions registered with userfaultfd. > .IP > The returned > .I ioctls > diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 > index 1741ee3..3c5b9c0 100644 > --- a/man2/userfaultfd.2 > +++ b/man2/userfaultfd.2 > @@ -172,6 +172,29 @@ or > .BR ioctl (2) > operations to resolve the page fault. > .PP > +Starting from Linux 4.14, if application sets > +.B UFFD_FEATURE_SIGBUS > +feature bit using > +.B UFFDIO_API > +.BR ioctl (2), > +no page fault notification will be forwarded to > +the user-space, instead a > +.B SIGBUS > +signal is delivered to the faulting process. With this feature, > +userfaultfd can be used for robustness purpose to simply catch > +any access to areas within the registered address range that do not > +have pages allocated, without having to listen to userfaultfd events. > +No userfaultfd monitor will be required for dealing with such memory > +accesses. For example, this feature can be useful for applications that > +want to prevent the kernel from automatically allocating pages and filling > +holes in sparse files when the hole is accessed thru mapped address. > +.PP > +The > +.B UFFD_FEATURE_SIGBUS > +feature is implicitly inherited through fork() if used in combination with > +.BR UFFD_FEATURE_FORK . > + > +.PP > Details of the various > .BR ioctl (2) > operations can be found in > -- > 2.7.4 > -- Sincerely yours, Mike.
