From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by kanga.kvack.org (Postfix) with ESMTP id 491768E0002 for ; Sat, 12 Jan 2019 19:14:55 -0500 (EST) Received: by mail-qk1-f199.google.com with SMTP id j125so13029447qke.12 for ; Sat, 12 Jan 2019 16:14:55 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id q6sor80054998qtb.53.2019.01.12.16.14.54 for (Google Transport Security); Sat, 12 Jan 2019 16:14:54 -0800 (PST) From: Joel Fernandes Subject: [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal Date: Sat, 12 Jan 2019 19:14:45 -0500 Message-Id: <20190113001446.158789-2-joel@joelfernandes.org> In-Reply-To: <20190113001446.158789-1-joel@joelfernandes.org> References: <20190113001446.158789-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: linux-kernel@vger.kernel.org, mtk.manpages@gmail.com Cc: "Joel Fernandes (Google)" , Andrew Morton , Andy Lutomirski , dancol@google.com, Hugh Dickins , Jann Horn , John Stultz , linux-api@vger.kernel.org, linux-man@vger.kernel.org, linux-mm@kvack.org, marcandre.lureau@redhat.com, Matthew Wilcox , Mike Kravetz , Shuah Khan , Stephen Rothwell From: "Joel Fernandes (Google)" More details of the seal can be found in the LKML patch: https://lore.kernel.org/lkml/20181120052137.74317-1-joel@joelfernandes.org/T/#t Signed-off-by: Joel Fernandes (Google) --- man2/fcntl.2 | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/man2/fcntl.2 b/man2/fcntl.2 index 03533d65b..54772f949 100644 --- a/man2/fcntl.2 +++ b/man2/fcntl.2 @@ -1525,6 +1525,21 @@ Furthermore, if there are any asynchronous I/O operations .RB ( io_submit (2)) pending on the file, all outstanding writes will be discarded. +.TP +.BR F_SEAL_FUTURE_WRITE +If this seal is set, the contents of the file can be modified only from +existing writeable mappings that were created prior to the seal being set. +Any attempt to create a new writeable mapping on the memfd via +.BR mmap (2) +will fail with +.BR EPERM. +Also any attempts to write to the memfd via +.BR write (2) +will fail with +.BR EPERM. +This is useful in situations where existing writable mapped regions need to be +kept intact while preventing any future writes. For example, to share a +read-only memory buffer to other processes that only the sender can write to. .\" .SS File read/write hints Write lifetime hints can be used to inform the kernel about the relative -- 2.20.1.97.g81188d93c3-goog