From: "Joel Fernandes (Google)" <joel@joelfernandes.org>
To: linux-kernel@vger.kernel.org, mtk.manpages@gmail.com
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@kernel.org>,
dancol@google.com, Jann Horn <jannh@google.com>,
John Stultz <john.stultz@linaro.org>,
kernel-team@android.com, linux-api@vger.kernel.org,
linux-man@vger.kernel.org, linux-mm@kvack.org,
Matthew Wilcox <willy@infradead.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Shuah Khan <shuah@kernel.org>,
Stephen Rothwell <sfr@canb.auug.org.au>
Subject: [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal
Date: Thu, 14 Mar 2019 17:48:43 -0400 [thread overview]
Message-ID: <20190314214844.207430-2-joel@joelfernandes.org> (raw)
In-Reply-To: <20190314214844.207430-1-joel@joelfernandes.org>
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) <joel@joelfernandes.org>
---
man2/fcntl.2 | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/man2/fcntl.2 b/man2/fcntl.2
index fce4f4c2b3bd..e01e2c075b5b 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
--
2.21.0.360.g471c308f928-goog
next prev parent reply other threads:[~2019-03-14 21:49 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-14 21:48 [PATCH -manpage 0/2] Joel Fernandes (Google)
2019-03-14 21:48 ` Joel Fernandes (Google) [this message]
2020-02-08 11:58 ` [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal Michael Kerrisk (man-pages)
2019-03-14 21:48 ` [PATCH -manpage 2/2] memfd_create.2: " Joel Fernandes (Google)
2020-02-08 11:58 ` Michael Kerrisk (man-pages)
-- strict thread matches above, loose matches on Subject: below --
2019-01-13 0:14 [PATCH -manpage 0/2] Document " Joel Fernandes
2019-01-13 0:14 ` [PATCH -manpage 1/2] fcntl.2: Update manpage with new " Joel Fernandes
2018-12-12 22:05 Joel Fernandes (Google)
2018-11-20 5:25 Joel Fernandes (Google)
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