diff mbox series

[-manpage,1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal

Message ID 20190314214844.207430-2-joel@joelfernandes.org (mailing list archive)
State New, archived
Headers show
Series [-manpage,1/2] fcntl.2: Update manpage with new memfd F_SEAL_FUTURE_WRITE seal | expand

Commit Message

Joel Fernandes (Google) March 14, 2019, 9:48 p.m. UTC
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(+)

Comments

Michael Kerrisk (man-pages) Feb. 8, 2020, 11:58 a.m. UTC | #1
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@joelfernandes.org/T/#t
>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

Thanks. Patch (finally) applied!

Cheers,

Michael


> ---
>  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
>
diff mbox series

Patch

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