Date: Fri, 10 Nov 2000 18:19:50 GMT From: nick@flirble.org To: FreeBSD-gnats-submit@freebsd.org Subject: kern/22754: mmap man page states non-page offsets do not work Message-ID: <200011101819.SAA46830@thinking-cap.babyhippo.co.uk>
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>Number: 22754
>Category: kern
>Synopsis: mmap man page states that non-page aligned offsets don't work. they do.
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: doc-bug
>Submitter-Id: current-users
>Arrival-Date: Fri Nov 10 10:30:01 PST 2000
>Closed-Date:
>Last-Modified:
>Originator: Nicholas Clark
>Release: FreeBSD 4.0-RELEASE i386
>Organization:
>Environment:
FreeBSD thinking-cap.babyhippo.co.uk 4.0-RELEASE FreeBSD 4.0-RELEASE #0: Mon Mar 20 22:50:22 GMT 2000 root@monster.cdrom.com:/usr/src/sys/compile/GENERIC i386
Anything else needed here?
>Description:
the mmap man page states in the BUGS section:
We currently can only deal with page aligned file offsets.
This doesn't appear to be true as mmap() will map /etc/motd without error
at offset 11. I assume that the documentation is out of date.
>How-To-Repeat:
#include <unistd.h>
#include <sys/mman.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
int main () {
int motd = open ("/etc/motd", O_RDONLY);
void *mapped;
if (motd < 0) {
perror ("Failed to open /etc/motd");
return 1;
}
mapped = mmap(NULL, 1024, PROT_EXEC | PROT_READ | PROT_WRITE , MAP_PRIVATE, motd, 11);
printf ("mapped = %p errno = %d\n", mapped, errno);
return 0;
}
gives
mapped = 0x280f000b errno = 0
on FreeBSD 3.4-STABLE, 4.0-RELEASE and 4.1-STABLE, all x86 (all I have access
to)
which isn't what the man page says should happen.
>Fix:
Ammend man page to remove this from the bugs. (It doesn't appear to be
just regular files, as /dev/zero also works)
Or if not all devices support it, state this in the BUGS section.
>Release-Note:
>Audit-Trail:
>Unformatted:
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