linux-kernel - [PATCH man-pages 3/5] ioctl_userfaultfd.2: add BUGS section

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Date:   Mon,  1 May 2017 08:43:17 +0300
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-man@...r.kernel.org, Mike Rapoport <rppt@...ux.vnet.ibm.com>
Subject: [PATCH man-pages 3/5] ioctl_userfaultfd.2: add BUGS section

The features handshake is not quite convenient.
Elaborate about it in the BUGS section.

Signed-off-by: Mike Rapoport <rppt@...ux.vnet.ibm.com>
---
 man2/ioctl_userfaultfd.2 | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/man2/ioctl_userfaultfd.2 b/man2/ioctl_userfaultfd.2
index e12b9de..50316de 100644
--- a/man2/ioctl_userfaultfd.2
+++ b/man2/ioctl_userfaultfd.2
@@ -650,6 +650,15 @@ operations are Linux-specific.
 .SH EXAMPLE
 See
 .BR userfaultfd (2).
+.SH BUGS
+In order to detect available userfault features and
+enable certain subset of those features
+the usefault file descriptor must be closed after the first
+.BR UFFDIO_API
+operation that queries features availability and re-opened before
+the second
+.BR UFFDIO_API
+call that actually enables the desired features.
 .SH SEE ALSO
 .BR ioctl (2),
 .BR mmap (2),
-- 
1.9.1