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Subject: Re: POSIX.Memory_Mapping.Map_Memory
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From: Mark Lorenzen <mark.lorenzen@ofir.dk>
Date: 29 Jan 2005 19:44:36 +0100
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Date: 2005-01-29T19:44:36+01:00
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"Adrian Hoe" <byhoe@greenlime.com> writes:

> Mark Lorenzen wrote:
> > "Adrian Hoe" <byhoe@greenlime.com> writes:
> >
> > > Hi,
> > >
> > > I am working on video_device with Video_4_Linux based on the work
> of
> > > Anders Gidenstam. According to latest V4L documentation, capturing
> with
> > > Read has been deprecated and the only method now is by the use of
> mmap.
> >
> 
> >>>> snip <<<<
> 
> 
> > > Device.Fd := Open (To_POSIX_String (File_Name),
> > > Read_Only);
> >
> > You open the device in read-only.
> >
> > [cut]
> >
> > >
> > > -- Permission Denied exception was raised here at the line below!!!
> > > Map := Map_Memory (System.Storage_Elements.Storage_Offset
> > > (Buf_Size),
> > > POSIX.Memory_Mapping.Allow_Read +
> > > POSIX.Memory_Mapping.Allow_Write,
> > > POSIX.Memory_Mapping.Map_Shared,
> > > Device.Fd,
> > > 0);
> >
> > But you try to map it in read/write mode.
> 
> I open with Read_Write option and raised POSIX.POSIX_ERROR :
> INVALID_ARGUMENT at the same line.

In the way you are using Map_Memeory, it is probably because the value
of Offset (i.e. 0) is not page aligned.

On many implementations, you can only map a multiple of the page size
and the memory has to be page aligned.

> 
> > Maybe thats the case of the exception. Do you have to be root in
> order
> > to open the device at all?
> 
> 
> No, I don't have to be root to open the device. Some applications are
> able to open it and the camera and video card work.
> 
> 
> 
> --
> Adrian Hoe

- Mark Lorenzen