I strongly recommend you switch to Beta15 and use the shared memory
there that is thanks to Thomas, Paolo, and Michael.
On Fri, Sep 17, 1999 at 11:07:34AM -0400, Dresner, Norman A. wrote:
> I'm trying to set up shared memory using the example at
> http://www.isd.cme.nist.gov/projects/emc/shmem.html
> in user-space but using the MAP_FIXED qualifier, I get a strange return from
> mmap() as follows:
> 1. The value of the pointer returned is 0
> 2. No error is declared (errno = 0 on return)
>
> The 0-pointer points to memory filled with 0's. If I use the original
> address (as I should be able to with MAP_FIXED), I get a segmentation fault.
> If I use the pointer mmap-ed without the MAP_FIXED qualifier, it accesses
> the memory perfectly. It doesn't matter in which order I do the two mmap()
> calls -- or if I only do the MAP_FIXED.
>
> The setup is as follows:
> 1. IBM Personal Computer 350 with an Intel P133 processor
> 2. 64 MB RAM
> 3. Red Hat 5.2
> 4. RT-Linux 0.9J
> 5. lilo.conf contains: append="mem=60m"
> 6. #include-ing <asm/page.h> shows a page size of 4K
>
> I really want to use the MAP_FIXED qualifier because I'm porting some legacy
> code that has pointers in the data that will be kept in shared memory and
> I'd like to be able to use the pointer values directly without modifying
> either the user-space or the rt-module code.
>
> Obviously I could modify the code so that only the offset from the start of
> shared memory is stored in the data and the accessing code in both
> user-space and kernel-space to add their respective base-pointer value to
> the offset, but that greatly increases the chances for error in what is
> already debugged and working code being ported from MS-DOS/AMX.
>
> Any help would be appreciated.
>
> Norm
>
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