why not allow another process access to share memory of xvfb?

[xin zhang]

thank you you all! now i understand the reason and solution.

2010/6/10 Daniel Stone <daniel at fooishbar.org>
>
> On Thu, Jun 10, 2010 at 03:10:52PM +0800, xin zhang wrote:
> > Hi experts:
> >     In Xvfb implementation, the frame buffer is allocated with IPC_PRIVATE
> > if uses SHM.
> >     Given that IPC_PRIVATE is just useful to parent/child process, and given
> > X is a single process,
> >     I don't realize what is the use.
> >     Why not add a param which allows user pass a string to produce IPC key,
> > and create share memory
> >     with the key, then other process will really access to the frame buffer.
> >     I think this will benefit many softwares, e.g. VNC, there is no need to
> > write an individual X server, just
> >     do an extension hooks on Xvfb is OK.
> >
> >     Does anyone know the reason? is it for security? thank you.
>
> Because direct access to the framebuffer might get you anything,
> including corruption if you access it in the middle of a copy.  If you
> want to get the framebuffer contents through SHM, use XShmGetImage().
>
> Cheers,
> Daniel
>
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