[forum] XFree86 5.0 TODO

Marc Aurele La France forum@XFree86.Org
Tue, 25 Mar 2003 15:34:06 -0700 (MST)


On Tue, 25 Mar 2003, Mark Vojkovich wrote:

> On 25 Mar 2003, Juliusz Chroboczek wrote:

> > L> So in it's current form DGA is pretty useless even when we ignore
> > L> it's sequrity problems.

> > There's at least one legitimate use of DGA that I can see.  I believe
> > it's the only one.

> > Consider a client that is doing its rendering client-side, but cannot
> > render to a shared-memory image, for example because it's using a
> > library that insists on rendering in buffers it allocates itself, or
> > because it's generating images in a non-X format.

> > Such a client will need to do a copy (possibly changing formats on the
> > fly) from system memory to the framebuffer.  Because it didn't render
> > to shm, it needs to do two copies -- either client buffer to shm to
> > framebuffer (ShmPutImage), or else client buffer to socket buffer to
> > framebuffer (PutImage).  With DGA, it can do a single copy, and thus
> > limit both memory access and cache pollution.

> > As I've said, I believe this to be the only legitimate application of
> > DGA, and I only know of it being actually required in video players
> > that use third-party codecs and that don't enjoy the benefits of Xv.
> > Whether this justifies the continuing existence of DGA (which highly
> > competent people tend to strongly dislike) is not something I can judge.

>    This is only a legitimate usage when in DGA mode.  Many of the
> players I've seen use DGA to get the framebuffer address and then
> use that outside of the relatively safe full-screen mode to render
> to the root window, which is not safe at all.

So, what about VMWare?  I'm not saying its use of DGA is legitimate nor
that DGA can't be replaced, but at some point we'll need to say something
to its installed base.

Marc.

+----------------------------------+-----------------------------------+
|  Marc Aurele La France           |  work:   1-780-492-9310           |
|  Computing and Network Services  |  fax:    1-780-492-1729           |
|  352 General Services Building   |  email:  tsi@ualberta.ca          |
|  University of Alberta           +-----------------------------------+
|  Edmonton, Alberta               |                                   |
|  T6G 2H1                         |     Standard disclaimers apply    |
|  CANADA                          |                                   |
+----------------------------------+-----------------------------------+
XFree86 Core Team member.  ATI driver and X server internals.