Re: [PATCH] Userfaultfd: Add description for UFFD_FEATURE_SIGBUS
From: Andrea Arcangeli <hidden>
Date: 2017-10-07 14:44:19
Also in:
linux-man, linux-mm, lkml
Hello Prakash, On Fri, Oct 06, 2017 at 07:52:20PM -0700, Prakash Sangappa wrote:
quoted hunk ↗ jump to hunk
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 [off-list ref] Date: Wed Sep 6 16:23:39 2017 -0700 mm: userfaultfd: add feature to request for a signal delivery Signed-off-by: Prakash Sangappa <redacted> --- man2/ioctl_userfaultfd.2 | 9 +++++++++ man2/userfaultfd.2 | 17 +++++++++++++++++ 2 files changed, 26 insertions(+)diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2 index 60fd29b..cfc65ae 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(
space after events?
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+.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 handling +page-fault events. .IP The returned .I ioctlsdiff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 index 1741ee3..a033742 100644 --- a/man2/userfaultfd.2 +++ b/man2/userfaultfd.2@@ -172,6 +172,23 @@ 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 deal with page-fault events.
",without having to listen to userfaultfd events." may be more clear.
+No userfaultd monitor will be required for handling page faults. For
^ typo: userfaultfd
+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
Maybe also mention that "The UFFD_FEATURE_SIGBUS feature is implicitly inherited through fork() if used in combination with UFFD_FEATURE_FORK." -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html