[v7] mremap.2: Add information for MREMAP_DONTUNMAP.
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Message ID 20200221174248.244748-3-bgeffon@google.com
State New
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  • [v7] mremap.2: Add information for MREMAP_DONTUNMAP.
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Commit Message

Brian Geffon Feb. 21, 2020, 5:42 p.m. UTC
Signed-off-by: Brian Geffon <bgeffon@google.com>
---
 man2/mremap.2 | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

Comments

Vlastimil Babka Feb. 25, 2020, 1:51 p.m. UTC | #1
On 2/21/20 6:42 PM, Brian Geffon wrote:
> @@ -209,10 +227,20 @@ 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.

So this can also result with MREMAP_FIXED, no?

> +.RE
>  .SH CONFORMING TO
>  This call is Linux-specific, and should not be used in programs
>  intended to be portable.
>
Brian Geffon Feb. 25, 2020, 5:48 p.m. UTC | #2
Yes, you're correct that is poorly worded. I'll send an updated
manpage closer to the release of this in case anything else changes.
Thanks for taking a look.

Brian

On Tue, Feb 25, 2020 at 5:51 AM Vlastimil Babka <vbabka@suse.cz> wrote:
>
> On 2/21/20 6:42 PM, Brian Geffon wrote:
> > @@ -209,10 +227,20 @@ 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.
>
> So this can also result with MREMAP_FIXED, no?
>
> > +.RE
> >  .SH CONFORMING TO
> >  This call is Linux-specific, and should not be used in programs
> >  intended to be portable.
> >
>

Patch
diff mbox series

diff --git a/man2/mremap.2 b/man2/mremap.2
index d73fb64fa..54ec67b20 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 5.7)"
+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 +207,17 @@  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 *
+.B MREMAP_DONTUNMAP
+was specified and \fIold_size\fP was not equal to \fInew_size\fP;
+.IP *
 \fIold_size\fP was zero and \fIold_address\fP does not refer to a
 shareable mapping (but see BUGS);
 .IP *
@@ -209,10 +227,20 @@  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.