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Subject: Re: POSIX.Memory_Mapping.Map_Memory
References: <1107014307.952357.216870@f14g2000cwb.googlegroups.com>
From: Mark Lorenzen <mark.lorenzen@ofir.dk>
Date: 29 Jan 2005 17:20:27 +0100
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Date: 2005-01-29T17:20:27+01:00
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"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.
> 
> I open a device and read the device with the following procedures, Open
> and Map_Image as below. In Procedure Map_Image, I make a call to
> Map_Memory (POSIX.Memory_Mapping) and raise an exception:
> 
> POSIX.POSIX_ERROR : PERMISSION_DENIED
> 
> -----------------------------------------------------------------------

[cut]

> 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.

Maybe thats the case of the exception. Do you have to be root in order
to open the device at all?

[cut]

> Adrian Hoe

- Mark Lorenzen