Re: [PATCH] mremap.2: Add information for MREMAP_DONTUNMAP.

Re: [PATCH] mremap.2: Add information for MREMAP_DONTUNMAP.

[Christian Brauner]

This seems to miss hitting the correct mailing list: 
mtk.manpages@gmail.com
linux-man@vger.kernel.org

Christian

On Fri, Feb 07, 2020 at 12:21:24PM -0800, Brian Geffon wrote:
> Signed-off-by: Brian Geffon <bgeffon@google.com>
> ---
>  man2/mremap.2 | 27 ++++++++++++++++++++++++++-
>  1 file changed, 26 insertions(+), 1 deletion(-)
> 
> diff --git a/man2/mremap.2 b/man2/mremap.2
> index d73fb64fa..c660a45be 100644
> --- a/man2/mremap.2
> +++ b/man2/mremap.2
> @@ -26,7 +26,8 @@
>  .\" 1996-04-12 Tom Bjorkholm <tomb@mydata.se>
>  .\"            Update for Linux 1.3.87 and later
>  .\" 2005-10-11 mtk: Added NOTES for MREMAP_FIXED; revised EINVAL text.
> -.\"
> +.\" 2020-02-05 Brian Geffon <bgeffon@google.com>
> +.\"            Update for MREMAP_DONTUNMAP.
>  .TH MREMAP 2 2019-03-06 "Linux" "Linux Programmer's Manual"
>  .SH NAME
>  mremap \- remap a virtual memory address
> @@ -129,6 +130,13 @@ If
>  is specified, then
>  .B MREMAP_MAYMOVE
>  must also be specified.
> +.TP
> +.BR MREMAP_DONTUNMAP " (since Linux ?.?)"
> +This flag which must be used in conjuction with
> +.B MREMAP_MAYMOVE
> +remaps a mapping to a new address and it does not unmap the mapping at \fIold_address\fP. This flag can only be used with private anonymous mappings. Any access to the range specified at \fIold_address\fP after completion will result in a page fault. If a
> +.BR userfaultfd (2)
> +was registered on the mapping specified by \fIold_address\fP it will continue to watch that mapping for faults.
>  .PP
>  If the memory segment specified by
>  .I old_address
> @@ -176,6 +184,8 @@ a value other than
>  .B MREMAP_MAYMOVE
>  or
>  .B MREMAP_FIXED
> +or
> +.B MREMAP_DONTUNMAP
>  was specified in
>  .IR flags ;
>  .IP *
> @@ -197,9 +207,14 @@ and
>  .IR old_size ;
>  .IP *
>  .B MREMAP_FIXED
> +or
> +.B MREMAP_DONTUNMAP
>  was specified without also specifying
>  .BR MREMAP_MAYMOVE ;
>  .IP *
> +.B MREMAP_DONTUNMAP
> +was specified with an \fIold_address\fP that was not private anonymous;
> +.IP *
>  \fIold_size\fP was zero and \fIold_address\fP does not refer to a
>  shareable mapping (but see BUGS);
>  .IP *
> @@ -209,10 +224,20 @@ flag was not specified.
>  .RE
>  .TP
>  .B ENOMEM
> +Not enough memory was available to complete the operation.
> +Possible causes are:
> +.RS
> +.IP * 3
>  The memory area cannot be expanded at the current virtual address, and the
>  .B MREMAP_MAYMOVE
>  flag is not set in \fIflags\fP.
>  Or, there is not enough (virtual) memory available.
> +.IP *
> +.B MREMAP_DONTUNMAP
> +was used without
> +.B MREMAP_FIXED
> +causing a new mapping to be created that would exceed the virtual memory available or it would exceed the maximum number of allowed mappings.
> +.RE
>  .SH CONFORMING TO
>  This call is Linux-specific, and should not be used in programs
>  intended to be portable.
> -- 
> 2.25.0.341.g760bfbb309-goog
>