From: cmlee@netcom.com (Chen-Ming Lee)
Subject: mmap() error:  "Out of memory"
Date: Wed, 5 May 1993 09:04:40 GMT

Hi all!

I am trying to use mmap() to emulate share memory.  However, it's
always giving me "Out of memory" error no matter how I set it up.
Has any one tried to use it with success?

Here's a sample code:

main()
{
   int  fd;
   char *mptr;
    
   fd=open("foo", O_RDONLY); 
   mptr=mmap(0, sizeof(int),PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
   /* 
   ** At this point mptr gets the return value of -1 no matter how
   ** I vary the parameters to mmap().
   */
}

Thanks for the help!


- Tom, cmlee@netcom.com
-- 
Tom, cmlee@netcom.com, cmlee@soda.berkeley.edu
--

From: haible@ma2s3.uucp (Bruno Haible)
Subject: Re: mmap() error:  "Out of memory"
Date: 5 May 1993 16:33:22 GMT

cmlee@netcom.com (Chen-Ming Lee) writes:
> main()
> {
>    int  fd;
>    char *mptr;
>    
>    fd=open("foo", O_RDONLY); 
>    mptr=mmap(0, sizeof(int),PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
>    /* 
>    ** At this point mptr gets the return value of -1 no matter how
>    ** I vary the parameters to mmap().
>    */
> }

You cannot use O_RDONLY in combination with PROT_WRITE.
Use  O_RDONLY  and  PROT_READ  if you want read access only,
O_RDWR  and  PROT_READ|PROT_WRITE  if you need read/write access
to your file "foo".

                    Bruno Haible
                    haible@ma2s2.mathematik.uni-karlsruhe.de

From: sct@dcs.ed.ac.uk (Stephen Tweedie)
Subject: Re: mmap() error:  "Out of memory"
Date: 6 May 93 11:57:44 GMT

On 5 May 93 09:04:40 GMT, cmlee@netcom.com (Chen-Ming Lee) said:

> I am trying to use mmap() to emulate share memory.  However, it's
> always giving me "Out of memory" error no matter how I set it up.
> Has any one tried to use it with success?

No!

Linux does not yet have full mmap() support.  If you want shared
memory, you can get the excellent ipcdelta set of Linux patches which
implement the SysV IPC routines - shared memory, message queues and
semaphores.

Cheers,
 Stephen Tweedie.
---
Stephen Tweedie < sct@uk.ac.ed.dcs>   (Internet: < sct@dcs.ed.ac.uk>)
Department of Computer Science, Edinburgh University, Scotland.