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

Brian Geffon
2020-02-07T20:21:48Z

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