mirror of https://github.com/mkerrisk/man-pages
90 lines
2.8 KiB
Groff
90 lines
2.8 KiB
Groff
.\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.TH GETPAGESIZE 2 2001-12-21 "Linux 2.5.0" "Linux Programmer's Manual"
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.SH NAME
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getpagesize \- get memory page size
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.SH SYNOPSIS
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.B #include <unistd.h>
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.sp
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.B int getpagesize(void);
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.SH DESCRIPTION
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The function
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.BR getpagesize ()
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returns the number of bytes in a page, where a "page" is the thing
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used where it says in the description of
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.BR mmap (2)
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that files are mapped in page-sized units.
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The size of the kind of pages that
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.BR mmap ()
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uses, is found using
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.RS
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.nf
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#include <unistd.h>
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long sz = sysconf(_SC_PAGESIZE);
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.fi
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.RE
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(most systems allow the synonym _SC_PAGE_SIZE for _SC_PAGESIZE),
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or
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.RS
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.nf
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#include <unistd.h>
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int sz = getpagesize();
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.fi
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.RE
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.SH HISTORY
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This call first appeared in 4.2BSD.
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.SH CONFORMING TO
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SVr4, 4.4BSD, SUSv2.
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In SUSv2 the
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.BR getpagesize ()
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call is labeled LEGACY, and in POSIX.1-2001
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it has been dropped;
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HP-UX does not have this call.
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Portable applications should employ
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.I sysconf(_SC_PAGESIZE)
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instead of this call.
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.SH NOTES
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Whether
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.BR getpagesize ()
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is present as a Linux system call depends on the architecture.
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If it is, it returns the kernel symbol PAGE_SIZE,
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which is architecture and machine model dependent.
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Generally, one uses binaries that are architecture but not
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machine model dependent, in order to have a single binary
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distribution per architecture.
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This means that a user program
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should not find PAGE_SIZE at compile time from a header file,
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but use an actual system call, at least for those architectures
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(like sun4) where this dependency exists.
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Here libc4, libc5, glibc 2.0 fail because their
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.BR getpagesize ()
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returns a statically derived value, and does not use a system call.
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Things are OK in glibc 2.1.
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.SH "SEE ALSO"
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.BR mmap (2),
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.BR sysconf (3)
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