Shared memory mapping question.

[Conor P. Cahill]

In article <9464 at discus.technion.ac.il> devil%techunix.bitnet at jade.berkeley.edu (Gil Tene) writes:
>My problem is : How do i "allocate" a specific area in process virtual space,
>in order to map the shared memory into it. How can i specify this virtual
>process address as a constant, and where do i take it from (top of user
>vir. address space, etc.). Allocating using sbrk() or malloc() variaties,
>doesn't give me any way to control the exact address of the allocated block...

Pulling an old response out of the saved bucket:

  From cpcahil Wed Nov  1 09:37:04 1989
  Path: virtech!cpcahil
  From: cpcahil at virtech.uucp (Conor P. Cahill)
  Newsgroups: comp.unix.questions
  Subject: Re: Shared memory and pointers
  Message-ID: <1989Nov1.143704.9258 at virtech.uucp>
  Date: 1 Nov 89 14:37:04 GMT
  References: <525 at wizard.UUCP>
  Distribution: usa
  Organization: Virtual Technologies Inc.
  Lines: 24
  
  In article <525 at wizard.UUCP>, john at wizard.UUCP (John Danner) writes:
  > group, neither of which are very clean.  First, make sure that every client
  > maps each block of shared memory to the same location.  Second, replace
  > pointers with something like objectID's and keep a table on the server which
  > has block #'s and offsets for each objectID.  
  
  I have seen 2 solutions to these problems.
  
  	1.  have the first program that creates the shared memory segment
  	attach it at whatever address it determins is appropriate and
  	then writes said address  into the first 4 bytes of the shared memory
  	segment itself.  All follow on program will attach the segment  at the
  	default address, read the address that it should be attached at, 
  	detach it, and finally re-attach it at the appropriate address.
  
  	2. keep track of data using relative pointers (offset from the 
  	begining of the shared memory segment) this is a real bear.
  
  
  
-- 
Conor P. Cahill            (703)430-9247        Virtual Technologies, Inc.,
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