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    SubjectRe: [test patch] dirty shared mappings

    On Fri, 9 Jan 1998, Thomas Sailer wrote:
    > >
    > > Really? I thought the standard UNIX shared memory definition was more like
    > > a shared memory block that has a public key (ie I thought _everybody_ got
    > > the shared memory area, not just children).
    > Everybody (with perms) can get it as long as it's not "unlinked"
    > (IPC_RMID). IPC_RMID removes the key (so no one new may attach),
    > but the segment retains until the last one unmaps it.
    > Don't know what happens on a fork after IPC_RMID, but I would
    > be very surprised if the child wouldn't get it mapped into
    > its address space.

    Note that when I'm saying "UNIX anonymous shared memory" as opposed to
    "SysV shmem" I'm talking about something like this:

    char * addr = mmap(NULL, 8192,
    -1, 0);

    And I thought that _everything_ shared the same page pool with no
    protection checks (ie different processes that aren't related would get
    the same shared pages).

    But if the above only gets a "private" shared memory area (ie only passed
    down as a shared memory area through fork(), not accessible through other
    unrelated processes doing the same mmap()), then it is not as braindamaged
    as I thought it was.


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