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Subject: Re: POSIX.Memory_Mapping.Map_Memory
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From: Mark Lorenzen <mark.lorenzen@ofir.dk>
Date: 30 Jan 2005 17:36:48 +0100
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Date: 2005-01-30T17:36:48+01:00
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Mark Lorenzen <mark.lorenzen@ofir.dk> writes:

> "Adrian Hoe" <byhoe@greenlime.com> writes:
> 
> > Mark Lorenzen wrote:
> > >
> > > I corrected the above mentioned problem and successfully opened and
> > > mapped a file. Strange.
> > 
> > Yes. I made a mistake. It should be:
> > 
> > if (buf == MAP_FAILED)
> > 
> > and it gave me error as well. And the strace says:
> > 
> > open("/dev/video0", O_RDWR)             = 3
> > mmap2(NULL, 230400, PROT_READ|PROT_WRITE, MAP_SHARED, 3, 0) = -1 EINVAL
> 
> I was just wondering: Is it allowed to map a device file as shared
> memory? Try to use MAP_PRIVATE instead of MAP_SHARED.

Furthermore: I do not think that it is possible to map character
special files, since it only allows sequential access. You can
probably only map block special files.

> 
> > (Invalid argument)
> > fstat64(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 1), ...}) = 0
> > m
> > 
> > mmap gives EINVAL in my C and Ada programs.
> > --
> > Adrian Hoe
> 
> - Mark Lorenzen