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Date: Thu, 5 Jun 97 12:09:52 EDT
From: luoqi@watermarkgroup.com (Luoqi Chen)
Message-Id: <9706051609.AA13720@watermarkgroup.com>
To: hackers@freebsd.org
Subject: discrepancy in mmap(2) about MAP_ANON
Sender: owner-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk


The mmap(2) man page:

     MAP_ANON    Map anonymous memory not associated with any specific file.
                 The file descriptor used for creating MAP_ANON regions is
                 used only for naming, and may be specified as -1 if no name
                 is associated with the region.

So a file descriptor other than -1 can be used with MAP_ANON, and along
with offset it names the mapped region (so it is possible to map the same
region at another address).

But in fact mmap() returns EINVAL. Here's the code in vm/vm_mmap.c,

        if (((flags & MAP_FIXED) && (addr & PAGE_MASK)) ||
            (ssize_t) uap->len < 0 || ((flags & MAP_ANON) && uap->fd != -1))
                return (EINVAL);