Date: Mon, 4 Aug 1997 19:22:36 -0500 (CDT) From: rtwalsh@ix.netcom.com To: questions@freebsd.org Subject: mmap and MAP_ANON Message-ID: <199784172215241@>
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Hello there,
Sorry to bug you with a question, but I couldn't find the answer anywhere, so here goes:
I am trying to create a "named" memory map, with the name being "69", as in the function call
below:
pMem1 = mmap( NULL, 100000, PROT_READ | PROT_WRITE, MAP_ANON | MAP_SHARED, 69, 0 );
However, this does not work (returns -1, with errno 22 (invalid argument)). If I use the invalid
fd of -1, then it does work, but then it is not named and I cannot get at this memory map from
another process. The man page for mmap() suggests that I should be able to do this:
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.
I am using FreeBSD 2.1.6. Is there a bug with this particular feature, or am I missing something?
If you cannot help me with this particular problem, perhaps you can give me a suggestion as to how
to solve the problem that I am trying to use this mmap for. I need to share memory between
processes and the data in the memory is confidential, thus the shared memory functions (shmget(),
etc.) are not appropriate, since anyone can use ipcs -m to get the shared memory id and write a
tiny program to go get the contents of the shared memory. Any suggestions as to how I can get a
moderately secure block of shared memory?
Many thanks for your time,
Robin.
---------------------
Robin Walsh
rtwalsh@ix.netcom.com
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