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ioctl_userfaultfd.2, userfaultfd.2: Add description for UFFD_FEATURE_SIGBUS 

Userfaultfd feature UFFD_FEATURE_SIGBUS was merged recently and
should be available in the Linux 4.14 release. This patch is for
the man page changes documenting this API.

Documents the following commit:

commit 2d6d6f5a09a96cc1fec7ed992b825e05f64cb50e
Author: Prakash Sangappa <prakash.sangappa@oracle.com>
Date: Wed Sep 6 16:23:39 2017 -0700

     mm: userfaultfd: add feature to request for a signal delivery

Reviewed-by: Andrea Arcangeli <aarcange@redhat.com>
Reviewed-by: Mike Rapoport <rppt@linux.vnet.ibm.com>
Signed-off-by: Prakash Sangappa <prakash.sangappa@oracle.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Prakash Sangappa 2017-10-09 15:45:51 -07:00 committed by Michael Kerrisk
parent cddd55a004
commit 2c371032cf
2 changed files with 32 additions and 0 deletions
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9
man2/ioctl_userfaultfd.2
View File

@ -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

23
man2/userfaultfd.2
View File

@ -171,6 +171,29 @@ or
.B UFFDIO_ZERO
.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)