man2/remap_file_pages.2

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  23 .\" 2003-12-10 Initial creation, Michael Kerrisk <mtk.manpages@gmail.com>
  24 .\" 2004-10-28 aeb, corrected prototype, prot must be 0
  25 .\"
  26 .TH REMAP_FILE_PAGES 2 2008-04-22 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 remap_file_pages \- create a non-linear file mapping
  29 .SH SYNOPSIS
  30 .nf
  31 .B #define _GNU_SOURCE
  32 .B #include <sys/mman.h>
  33 .sp
  34 .BI "int remap_file_pages(void *" addr ", size_t " size ", int " prot ,
  35 .BI "                     ssize_t " pgoff ", int " flags );
  36 .fi
  37 .SH DESCRIPTION
  38 The
  39 .BR remap_file_pages ()
  40 system call is used to create a non-linear mapping, that is, a mapping
  41 in which the pages of the file are mapped into a non-sequential order
  42 in memory.
  43 The advantage of using
  44 .BR remap_file_pages ()
  45 over using repeated calls to
  46 .BR mmap (2)
  47 is that the former approach does not require the kernel to create
  48 additional VMA (Virtual Memory Area) data structures.
  49
  50 To create a non-linear mapping we perform the following steps:
  51 .TP 3
  52 1.
  53 Use
  54 .BR mmap (2)
  55 to create a mapping (which is initially linear).
  56 This mapping must be created with the
  57 .B MAP_SHARED
  58 flag.
  59 .TP
  60 2.
  61 Use one or more calls to
  62 .BR remap_file_pages ()
  63 to rearrange the correspondence between the pages of the mapping
  64 and the pages of the file.
  65 It is possible to map the same page of a file
  66 into multiple locations within the mapped region.
  67 .LP
  68 The
  69 .I pgoff
  70 and
  71 .I size
  72 arguments specify the region of the file that is to be relocated
  73 within the mapping:
  74 .I pgoff
  75 is a file offset in units of the system page size;
  76 .I size
  77 is the length of the region in bytes.
  78
  79 The
  80 .I addr
  81 argument serves two purposes.
  82 First, it identifies the mapping whose pages we want to rearrange.
  83 Thus,
  84 .I addr
  85 must be an address that falls within
  86 a region previously mapped by a call to
  87 .BR mmap (2).
  88 Second,
  89 .I addr
  90 specifies the address at which the file pages
  91 identified by
  92 .I pgoff
  93 and
  94 .I size
  95 will be placed.
  96
  97 The values specified in
  98 .I addr
  99 and
 100 .I size
 101 should be multiples of the system page size.
 102 If they are not, then the kernel rounds
 103 .I both
 104 values
 105 .I down
 106 to the nearest multiple of the page size.
 107 .\" This rounding is weird, and not consistent with the treatment of
 108 .\" the analogous arguments for munmap()/mprotect() and for mlock().
 109 .\" MTK, 14 Sep 2005
 110
 111 The
 112 .I prot
 113 argument must be specified as 0.
 114
 115 The
 116 .I flags
 117 argument has the same meaning as for
 118 .BR mmap (2),
 119 but all flags other than
 120 .B MAP_NONBLOCK
 121 are ignored.
 122 .SH "RETURN VALUE"
 123 On success,
 124 .BR remap_file_pages ()
 125 returns 0.
 126 On error, \-1 is returned, and
 127 .I errno
 128 is set appropriately.
 129 .SH ERRORS
 130 .TP
 131 .B EINVAL
 132 .I addr
 133 does not refer to a valid mapping
 134 created with the
 135 .B MAP_SHARED
 136 flag.
 137 .TP
 138 .B EINVAL
 139 .IR addr ,
 140 .IR size ,
 141 .IR prot ,
 142 or
 143 .I pgoff
 144 is invalid.
 145 .\" And possibly others from vma->vm_ops->populate()
 146 .SH VERSIONS
 147 The
 148 .BR remap_file_pages ()
 149 system call appeared in Linux 2.5.46;
 150 glibc support was added in version 2.3.3.
 151 .SH "CONFORMING TO"
 152 The
 153 .BR remap_file_pages ()
 154 system call is Linux-specific.
 155 .SH "SEE ALSO"
 156 .BR getpagesize (2),
 157 .BR mmap (2),
 158 .BR mmap2 (2),
 159 .BR mprotect (2),
 160 .BR mremap (2),
 161 .BR msync (2),
 162 .BR feature_test_macros (7)