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Added an example program.

This commit is contained in:
Michael Kerrisk 2007-06-30 14:11:48 +00:00
parent dd9b25a6ca
commit 74fa61b798
1 changed files with 85 additions and 2 deletions
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87
man2/mmap.2
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@ -1,7 +1,7 @@
.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Copyright (C) 1996 Andries Brouwer <aeb@cwi.nl>
.\" and Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
.\" and Copyright (C) 2006, 2007 Michael Kerrisk <mtk-manpages@gmx.net>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
@ -34,8 +34,9 @@
.\" Modified 2004-12-08, from Eric Estievenart <eric.estievenart@free.fr>
.\" Modified 2004-12-08, mtk, formatting tidy-ups
.\" Modified 2006-12-04, mtk, various parts rewritten
.\" 2007-07-10, mtk, Added an example program.
.\"
.TH MMAP 2 2006-12-04 "Linux" "Linux Programmer's Manual"
.TH MMAP 2 2007-07-10 "Linux" "Linux Programmer's Manual"
.SH NAME
mmap, munmap \- map or unmap files or devices into memory
.SH SYNOPSIS
@ -489,6 +490,88 @@ Since kernel 2.6.12,
fails with the error
.B EINVAL
for this case.
.SH EXAMPLE
.PP
The following program prints part of the file specified in
its first command-line argument to standard output.
The range of bytes to be printed is specified via offset and length
values in the second and third command-line arguments.
The program creates a memory mapping of the required
pages of the file and then uses
.BR write (2)
to output the desired bytes.
.nf
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
char *addr;
int fd;
struct stat sb;
off_t offset, pa_offset;
size_t length;
ssize_t s;
if (argc < 3 || argc > 4) == 0) {
fprintf(stderr, "%s file offset [length]\\n", argv[0]);
exit(EXIT_FAILURE);
}
fd = open(argv[1], O_RDONLY);
if (fd == \-1) {
perror("open");
exit(EXIT_FAILURE);
}
if (fstat(fd, &sb) == \-1) { /* To obtain file size */
perror("fstat");
exit(EXIT_FAILURE);
}
offset = atoi(argv[2]);
pa_offset = offset & ~(sysconf(_SC_PAGE_SIZE) \- 1);
/* offset for mmap() must be page aligned */
if (offset >= sb.st_size) {
fprintf(stderr, "offset is past end of file\\n");
exit(EXIT_FAILURE);
}
if (argc == 4) {
length = atoi(argv[3]);
if (offset + length > sb.st_size)
length = sb.st_size \- offset;
/* Can't display bytes past end of file */
} else { /* No length arg ==> display to end of file */
length = sb.st_size \- offset;
}
addr = mmap(NULL, length + offset \- pa_offset, PROT_READ,
MAP_PRIVATE, fd, pa_offset);
if (addr == MAP_FAILED) {
perror("mmap");
exit(EXIT_FAILURE);
}
s = write(STDOUT_FILENO, addr + offset \- pa_offset, length);
if (s != length) {
if (s == \-1)
perror("write");
else
fprintf(stderr, "partial write");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
} /* main */
.fi
.SH "SEE ALSO"
.BR getpagesize (2),
.BR mincore (2),