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

Alan Coopersmith alan.coopersmith at oracle.com
Thu Jun 10 06:35:48 PDT 2010

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.

Already there - see the -fbdir option in the man page:


     -fbdir framebuffer-directory
         This option specifies the directory in which the  memory
         mapped files containing the framebuffer memory should be
         created.   See  FILES.   This  option  only  exists   on
         machines that have the mmap and msync system calls.

     The  following  files  are  created  if the -fbdir option is

         Memory mapped file  containing  screen  n's  framebuffer
         memory, one file per screen.  The file is in xwd format.
         Thus, taking a full-screen snapshot can be done  with  a
         file  copy command, and the resulting snapshot will even
         contain the cursor image.

	-Alan Coopersmith-        alan.coopersmith at oracle.com
	 Oracle Solaris Platform Engineering: X Window System

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