man2/remap_file_pages.2

   1 .\" Copyright (C) 2003, Michael Kerrisk (mtk-manpages@gmx.net)
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  20 .\" 2003-12-10 Initial creation, Michael Kerrisk <mtk-manpages@gmx.net>
  21 .\" 2004-10-28 aeb, corrected prototype, prot must be 0
  22 .\"
  23 .TH REMAP_FILE_PAGES 2 2004-10-28 "Linux 2.6" "Linux Programmer's Manual"
  24 .SH NAME
  25 remap_file_pages \- create a non-linear file mapping
  26 .SH SYNOPSIS
  27 .B #include <sys/mman.h>
  28 .sp
  29 .BI "int remap_file_pages(void *" start ", "
  30 .BI "size_t " size ", int " prot ", "
  31 .BI "ssize_t " pgoff ", int " flags );
  32 .SH DESCRIPTION
  33 The
  34 .BR remap_file_pages ()
  35 system call is used to create a non-linear mapping, that is, a mapping
  36 in which the pages of the file are mapped into a non-sequential order
  37 in memory.
  38 The advantage of using
  39 .BR remap_file_pages ()
  40 over using repeated calls to
  41 .BR mmap (2)
  42 is that the former approach does not require the kernel to create
  43 additional VMA (Virtual Memory Area) data structures.
  44
  45 To create a non-linear mapping we perform the following steps:
  46 .TP
  47 \fB1.\fp
  48 Use
  49 .BR mmap ()
  50 to create a mapping (which is initially linear).
  51 This mapping must be created with the
  52 MAP_SHARED flag.
  53 .TP
  54 \fB2.\fp
  55 Use one or more calls to
  56 .BR remap_file_pages ()
  57 to rearrange the correspondence between the pages of the mapping
  58 and the pages of the file.
  59 It is possible to map the same page of a file
  60 into multiple locations within the mapped region.
  61 .LP
  62 The
  63 .I pgoff
  64 and
  65 .I size
  66 arguments specify the region of the file that is to be relocated
  67 within the mapping:
  68 .I pgoff
  69 is a file offset in units of the system page size;
  70 .I size
  71 is the length of the region in bytes.
  72
  73 The
  74 .I start
  75 argument serves two purposes.
  76 First, it identifies the mapping whose pages we want to rearrange.
  77 Thus,
  78 .I start
  79 must be an address that falls within
  80 a region previously mapped by a call to
  81 .BR mmap ().
  82 Second,
  83 .I start
  84 specifies the address at which the file pages
  85 identified by
  86 .I pgoff
  87 and
  88 .I size
  89 will be placed.
  90
  91 The values specified in
  92 .I start
  93 and
  94 .I size
  95 should be multiples of the system page size.
  96 If they are not, then the kernel rounds
  97 .I both
  98 values
  99 .I down
 100 to the nearest multiple of the page size.
 101 .\" This rounding is weird, and not consistent with the treatment of
 102 .\" the analogous arguments for munmap()/mprotect() and for mlock().
 103 .\" MTK, 14 Sep 2005
 104
 105 The
 106 .I prot
 107 argument must be specified as 0.
 108
 109 The
 110 .I flags
 111 argument has the same meaning as for
 112 .BR mmap (),
 113 but all flags other than MAP_NONBLOCK are ignored.
 114 .SH "RETURN VALUE"
 115 On success,
 116 .BR remap_file_pages ()
 117 returns 0.
 118 On error, \-1 is returned, and
 119 .I errno
 120 is set appropriately.
 121 .SH NOTES
 122 The
 123 .BR remap_file_pages ()
 124 system call appeared in Linux 2.5.46.
 125 .SH ERRORS
 126 .TP
 127 .B EINVAL
 128 .I start
 129 does not refer to a valid mapping
 130 created with the MAP_SHARED flag.
 131 .TP
 132 .B EINVAL
 133 .IR start ,
 134 .IR size ,
 135 .IR prot ,
 136 or
 137 .I pgoff
 138 is invalid.
 139 .\" And possibly others from vma->vm_ops->populate()
 140 .SH "CONFORMING TO"
 141 The
 142 .BR remap_file_pages ()
 143 system call is Linux specific.
 144 .SH "SEE ALSO"
 145 .BR getpagesize (2),
 146 .BR mmap (2),
 147 .BR mmap2 (2),
 148 .BR mprotect (2),
 149 .BR mremap (2),
 150 .BR msync (2)