[patch v2] mremap.2: Add description of old_size == 0 functionality
From: Mike Kravetz <hidden>
Date: 2017-09-19 21:44:01
Also in:
linux-man, linux-mm, lkml
Subsystem:
the rest · Maintainer:
Linus Torvalds
v2: Fix incorrect wording noticed by Jann Horn.
Remove deprecated and memfd_create discussion as suggested
by Florian Weimer.
Since at least the 2.6 time frame, mremap would create a new mapping
of the same pages if 'old_size == 0'. It would also leave the original
mapping. This was used to create a 'duplicate mapping'.
A recent change was made to mremap so that an attempt to create a
duplicate a private mapping will fail.
Document the 'old_size == 0' behavior and new return code from
below commit.
commit dba58d3b8c5045ad89c1c95d33d01451e3964db7
Author: Mike Kravetz [off-list ref]
Date: Wed Sep 6 16:20:55 2017 -0700
mm/mremap: fail map duplication attempts for private mappings
Signed-off-by: Mike Kravetz <redacted>
---
man2/mremap.2 | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/man2/mremap.2 b/man2/mremap.2
index 98643c640..235984a96 100644
--- a/man2/mremap.2
+++ b/man2/mremap.2@@ -58,6 +58,20 @@ may be provided; see the description of .B MREMAP_FIXED below. .PP +If the value of \fIold_size\fP is zero, and \fIold_address\fP refers to +a shareable mapping (see +.BR mmap (2) +.BR MAP_SHARED ) +, then +.BR mremap () +will create a new mapping of the same pages. \fInew_size\fP +will be the size of the new mapping and the location of the new mapping +may be specified with \fInew_address\fP, see the description of +.B MREMAP_FIXED +below. If a new mapping is requested via this method, then the +.B MREMAP_MAYMOVE +flag must also be specified. +.PP In Linux the memory is divided into pages. A user process has (one or) several linear virtual memory segments.
@@ -174,7 +188,12 @@ and or .B MREMAP_FIXED was specified without also specifying -.BR MREMAP_MAYMOVE . +.BR MREMAP_MAYMOVE ; +or \fIold_size\fP was zero and \fIold_address\fP does not refer to a +shareable mapping; +or \fIold_size\fP was zero and the +.BR MREMAP_MAYMOVE +flag was not specified. .TP .B ENOMEM The memory area cannot be expanded at the current virtual address, and the
--
2.13.5
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