Re: [PATCH -manpage 1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal
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From: Michael Kerrisk (man-pages) <hidden>
Date: 2020-02-08 11:58:15
Also in:
linux-man, linux-mm, lkml
Hello Joel, On 3/14/19 10:48 PM, Joel Fernandes (Google) wrote:
More details of the seal can be found in the LKML patch: https://lore.kernel.org/lkml/20181120052137.74317-1-joel-QYYGw3jwrUn5owFQY34kdNi2O/JbrIOy@public.gmane.org/T/#t Signed-off-by: Joel Fernandes (Google) <joel-QYYGw3jwrUn5owFQY34kdNi2O/JbrIOy@public.gmane.org>
Thanks. Patch (finally) applied! Cheers, Michael
quoted hunk ↗ jump to hunk
--- 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
-- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/