Dresner, Norman A. wrote:
>
> I'm trying to set up shared memory
> 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 setup is as follows:
...
> 2. 64 MB RAM
...
> 5. lilo.conf contains: append="mem=60m"
You have specified to set aside exactly 4 MB of memory, since you have a
64 MB machine and mem=60m in /etc/lilo.conf. However, shared memory is
only set aside between where you tell Linux to stop (short of 60 MB) and
the next address evenly divisible by 4 MB, which is 60 MB. So, you have
no shared memory left.
If you need exactly 4 MB you are out of luck. Try this:
append="mem=61m"
for 3 MB of shared memory. You can use hex numbers, e.g.,
append="mem=0x3D00000"
which makes it easier to compose amounts like 3.75 MB, e.g.,
append="mem=0x3C40000"
Check my hex math; you get the picture. I don't know how close to the
border you can get, e.g.,
append="mem=0x3C00001"
for one byte less than 4 MB may not work.
--Fred
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