man2/getpagesize.2

   1 .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .TH getpagesize 2 (date) "Linux man-pages (unreleased)"
   6 .SH NAME
   7 getpagesize \- get memory page size
   8 .SH LIBRARY
   9 Standard C library
  10 .RI ( libc ", " \-lc )
  11 .SH SYNOPSIS
  12 .nf
  13 .B #include <unistd.h>
  14 .P
  15 .B int getpagesize(void);
  16 .fi
  17 .P
  18 .RS -4
  19 Feature Test Macro Requirements for glibc (see
  20 .BR feature_test_macros (7)):
  21 .RE
  22 .P
  23 .BR getpagesize ():
  24 .nf
  25     Since glibc 2.20:
  26         _DEFAULT_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
  27     glibc 2.12 to glibc 2.19:
  28         _BSD_SOURCE || ! (_POSIX_C_SOURCE >= 200112L)
  29     Before glibc 2.12:
  30         _BSD_SOURCE || _XOPEN_SOURCE >= 500
  31 .\"        || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
  32 .fi
  33 .SH DESCRIPTION
  34 The function
  35 .BR getpagesize ()
  36 returns the number of bytes in a memory page,
  37 where "page" is a fixed-length block,
  38 the unit for memory allocation and file mapping performed by
  39 .BR mmap (2).
  40 .SH STANDARDS
  41 None.
  42 .SH HISTORY
  43 This call first appeared in 4.2BSD.
  44 SVr4, 4.4BSD, SUSv2.
  45 In SUSv2 the
  46 .BR getpagesize ()
  47 call is labeled LEGACY, and in POSIX.1-2001
  48 it has been dropped;
  49 HP-UX does not have this call.
  50 .SH NOTES
  51 Portable applications should employ
  52 .I sysconf(_SC_PAGESIZE)
  53 instead of
  54 .BR getpagesize ():
  55 .P
  56 .in +4n
  57 .EX
  58 #include <unistd.h>
  59 long sz = sysconf(_SC_PAGESIZE);
  60 .EE
  61 .in
  62 .P
  63 (Most systems allow the synonym
  64 .B _SC_PAGE_SIZE
  65 for
  66 .BR _SC_PAGESIZE .)
  67 .P
  68 Whether
  69 .BR getpagesize ()
  70 is present as a Linux system call depends on the architecture.
  71 If it is, it returns the kernel symbol
  72 .BR PAGE_SIZE ,
  73 whose value depends on the architecture and machine model.
  74 Generally, one uses binaries that are dependent on the architecture but not
  75 on the machine model, in order to have a single binary
  76 distribution per architecture.
  77 This means that a user program
  78 should not find
  79 .B PAGE_SIZE
  80 at compile time from a header file,
  81 but use an actual system call, at least for those architectures
  82 (like sun4) where this dependency exists.
  83 Here glibc 2.0 fails because its
  84 .BR getpagesize ()
  85 returns a statically derived value, and does not use a system call.
  86 Things are OK in glibc 2.1.
  87 .SH SEE ALSO
  88 .BR mmap (2),
  89 .BR sysconf (3)