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616c2730 | 1 | .\" Copyright (C) 2003, Michael Kerrisk <mtk.manpages@gmail.com> |
fea681da | 2 | .\" |
93015253 | 3 | .\" %%%LICENSE_START(VERBATIM) |
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4 | .\" Permission is granted to make and distribute verbatim copies of this |
5 | .\" manual provided the copyright notice and this permission notice are | |
6 | .\" preserved on all copies. | |
7 | .\" | |
8 | .\" Permission is granted to copy and distribute modified versions of this | |
9 | .\" manual under the conditions for verbatim copying, provided that the | |
10 | .\" entire resulting derived work is distributed under the terms of a | |
11 | .\" permission notice identical to this one. | |
12 | .\" | |
13 | .\" Since the Linux kernel and libraries are constantly changing, this | |
14 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
15 | .\" responsibility for errors or omissions, or for damages resulting from | |
10d76543 MK |
16 | .\" the use of the information contained herein. The author(s) may not |
17 | .\" have taken the same level of care in the production of this manual, | |
18 | .\" which is licensed free of charge, as they might when working | |
19 | .\" professionally. | |
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20 | .\" |
21 | .\" Formatted or processed versions of this manual, if unaccompanied by | |
22 | .\" the source, must acknowledge the copyright and authors of this work. | |
4b72fb64 | 23 | .\" %%%LICENSE_END |
fea681da | 24 | .\" |
c11b1abf | 25 | .\" 2003-12-10 Initial creation, Michael Kerrisk <mtk.manpages@gmail.com> |
fea681da MK |
26 | .\" 2004-10-28 aeb, corrected prototype, prot must be 0 |
27 | .\" | |
4b8c67d9 | 28 | .TH REMAP_FILE_PAGES 2 2017-09-15 "Linux" "Linux Programmer's Manual" |
fea681da | 29 | .SH NAME |
fb0e9c48 | 30 | remap_file_pages \- create a nonlinear file mapping |
fea681da | 31 | .SH SYNOPSIS |
e743a184 | 32 | .nf |
b80f966b | 33 | .BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */" |
fea681da | 34 | .B #include <sys/mman.h> |
68e4db0a | 35 | .PP |
14f5ae6d | 36 | .BI "int remap_file_pages(void *" addr ", size_t " size ", int " prot , |
aff9c307 | 37 | .BI " size_t " pgoff ", int " flags ); |
e743a184 | 38 | .fi |
fea681da | 39 | .SH DESCRIPTION |
85c984a1 MK |
40 | .BR Note : |
41 | .\" commit 33041a0d76d3c3e0aff28ac95a2ffdedf1282dbc | |
42 | .\" http://lwn.net/Articles/597632/ | |
94d76e41 MK |
43 | this system call was marked as deprecated starting with Linux 3.16. |
44 | In Linux 4.0, the implementation was replaced | |
45 | .\" commit c8d78c1823f46519473949d33f0d1d33fe21ea16 | |
46 | by a slower in-kernel emulation. | |
85c984a1 MK |
47 | Those few applications that use this system call should |
48 | consider migrating to alternatives. | |
94d76e41 MK |
49 | This change was made because the kernel code for this system call was complex, |
50 | and it is believed to be little used or perhaps even completely unused. | |
51 | While it had some use cases in database applications on 32-bit systems, | |
52 | those use cases don't exist on 64-bit systems. | |
efeece04 | 53 | .PP |
fea681da | 54 | The |
63aa9df0 | 55 | .BR remap_file_pages () |
fb0e9c48 | 56 | system call is used to create a nonlinear mapping, that is, a mapping |
24b74457 | 57 | in which the pages of the file are mapped into a nonsequential order |
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58 | in memory. |
59 | The advantage of using | |
63aa9df0 | 60 | .BR remap_file_pages () |
fea681da MK |
61 | over using repeated calls to |
62 | .BR mmap (2) | |
63 | is that the former approach does not require the kernel to create | |
64 | additional VMA (Virtual Memory Area) data structures. | |
efeece04 | 65 | .PP |
fb0e9c48 | 66 | To create a nonlinear mapping we perform the following steps: |
218dfacd MK |
67 | .TP 3 |
68 | 1. | |
fea681da | 69 | Use |
0bfa087b | 70 | .BR mmap (2) |
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71 | to create a mapping (which is initially linear). |
72 | This mapping must be created with the | |
c13182ef | 73 | .B MAP_SHARED |
16fd68e1 | 74 | flag. |
fea681da | 75 | .TP |
218dfacd | 76 | 2. |
fea681da | 77 | Use one or more calls to |
63aa9df0 | 78 | .BR remap_file_pages () |
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79 | to rearrange the correspondence between the pages of the mapping |
80 | and the pages of the file. | |
81 | It is possible to map the same page of a file | |
82 | into multiple locations within the mapped region. | |
dd3568a1 | 83 | .PP |
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84 | The |
85 | .I pgoff | |
86 | and | |
87 | .I size | |
88 | arguments specify the region of the file that is to be relocated | |
89 | within the mapping: | |
90 | .I pgoff | |
91 | is a file offset in units of the system page size; | |
92 | .I size | |
93 | is the length of the region in bytes. | |
efeece04 | 94 | .PP |
fea681da | 95 | The |
14f5ae6d | 96 | .I addr |
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97 | argument serves two purposes. |
98 | First, it identifies the mapping whose pages we want to rearrange. | |
99 | Thus, | |
14f5ae6d | 100 | .I addr |
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101 | must be an address that falls within |
102 | a region previously mapped by a call to | |
0bfa087b | 103 | .BR mmap (2). |
fea681da | 104 | Second, |
14f5ae6d | 105 | .I addr |
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106 | specifies the address at which the file pages |
107 | identified by | |
108 | .I pgoff | |
109 | and | |
110 | .I size | |
111 | will be placed. | |
efeece04 | 112 | .PP |
22b6a68b | 113 | The values specified in |
14f5ae6d | 114 | .I addr |
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115 | and |
116 | .I size | |
117 | should be multiples of the system page size. | |
118 | If they are not, then the kernel rounds | |
c13182ef MK |
119 | .I both |
120 | values | |
22b6a68b MK |
121 | .I down |
122 | to the nearest multiple of the page size. | |
c13182ef MK |
123 | .\" This rounding is weird, and not consistent with the treatment of |
124 | .\" the analogous arguments for munmap()/mprotect() and for mlock(). | |
22b6a68b | 125 | .\" MTK, 14 Sep 2005 |
efeece04 | 126 | .PP |
fea681da MK |
127 | The |
128 | .I prot | |
129 | argument must be specified as 0. | |
efeece04 | 130 | .PP |
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131 | The |
132 | .I flags | |
133 | argument has the same meaning as for | |
0bfa087b | 134 | .BR mmap (2), |
c13182ef MK |
135 | but all flags other than |
136 | .B MAP_NONBLOCK | |
16fd68e1 | 137 | are ignored. |
47297adb | 138 | .SH RETURN VALUE |
fea681da | 139 | On success, |
63aa9df0 | 140 | .BR remap_file_pages () |
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141 | returns 0. |
142 | On error, \-1 is returned, and | |
143 | .I errno | |
144 | is set appropriately. | |
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145 | .SH ERRORS |
146 | .TP | |
147 | .B EINVAL | |
14f5ae6d | 148 | .I addr |
fea681da | 149 | does not refer to a valid mapping |
c13182ef MK |
150 | created with the |
151 | .B MAP_SHARED | |
16fd68e1 | 152 | flag. |
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153 | .TP |
154 | .B EINVAL | |
14f5ae6d | 155 | .IR addr , |
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156 | .IR size , |
157 | .IR prot , | |
158 | or | |
159 | .I pgoff | |
160 | is invalid. | |
161 | .\" And possibly others from vma->vm_ops->populate() | |
a1d5f77c MK |
162 | .SH VERSIONS |
163 | The | |
164 | .BR remap_file_pages () | |
deec2da3 MK |
165 | system call appeared in Linux 2.5.46; |
166 | glibc support was added in version 2.3.3. | |
47297adb | 167 | .SH CONFORMING TO |
fea681da | 168 | The |
63aa9df0 | 169 | .BR remap_file_pages () |
8382f16d | 170 | system call is Linux-specific. |
8fd1fd30 | 171 | .SH NOTES |
7a085379 MK |
172 | Since Linux 2.6.23, |
173 | .\" commit 3ee6dafc677a68e461a7ddafc94a580ebab80735 | |
8fd1fd30 | 174 | .BR remap_file_pages () |
ea38fc5c | 175 | creates non-linear mappings only |
5991f44e | 176 | on in-memory filesystems such as |
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177 | .BR tmpfs (5), |
178 | hugetlbfs or ramfs. | |
76f26660 MK |
179 | On filesystems with a backing store, |
180 | .BR remap_file_pages () | |
181 | is not much more efficient than using | |
8fd1fd30 | 182 | .BR mmap (2) |
76f26660 | 183 | to adjust which parts of the file are mapped to which addresses. |
47297adb | 184 | .SH SEE ALSO |
fea681da MK |
185 | .BR getpagesize (2), |
186 | .BR mmap (2), | |
187 | .BR mmap2 (2), | |
188 | .BR mprotect (2), | |
189 | .BR mremap (2), | |
0a4f8b7b | 190 | .BR msync (2) |