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    SubjectRe: mmap'ed memory in core files ?
    Hi Michael,

    On Tue, Jul 01, 2008 at 08:16:11PM +0200, Michael Kerrisk wrote:
    > On 7/1/08, Philippe De Muyter <phdm@macqel.be> wrote:
    > > Hello everybody,
    > >
    > > I develop video acquisition software using the video1394 interface.
    > > The images grabbed by the camera and iee1394 bus are kept in kernel
    > > memory and made available to the user program through a mmap call done
    > > in the libdc1394 library :
    > >
    > > dma_ring_buffer= mmap(0, vmmap.nb_buffers * vmmap.buf_size,
    > > PROT_READ|PROT_WRITE,MAP_SHARED, craw->capture.dma_fd, 0);
    > >
    > > Sometimes, my program crashes and produces a core file :) It seems to
    > > me that the core file does not contain the mmap'ed memory and hence
    > > I cannot replay my program with the same image for debugging purpose.
    > >
    > > Is it possible to configure the kernel through /proc, or through the mmap
    > > system call to have that mmapped segment in the core file, or do I need
    > > to modify the kernel itself to obtain the behaviour I want ? If I
    > > need to modify the kernel, can some kind soul provide me some pointers ?
    >
    >
    > Have a look at the section "Controlling which mappings are written to
    > the core dump" in a recent core.5 man page:
    > http://www.kernel.org/doc/man-pages/online/pages/man5/core.5.html

    thanks for the info. I didn't know about /proc/PID/coredump_filter.

    that part was promising :

    bit 2 Dump file-backed private mappings.
    bit 3 Dump file-backed shared mappings.

    The default value of coredump_filter is 0x3; this reflects traditional
    Linux behavior and means that only anonymous memory segments are dumped.

    Unfortunately, the part that applies to me (I have tested it) is the next one :

    Memory-mapped I/O pages such as frame buffer are never dumped, [...],
    regardless of the coredump_filter value.

    Is that a design decision, or a mere finding of the way it is implemented
    now ?

    So, back to my original question :

    Can some kind soul provide me some pointers to the way I should modify
    the kernel to make the inclusion of the video1394 mmapped segment in
    core files possible ?

    best regards

    Philippe


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