Re: [HACKERS] mmap and MAP_ANON

>
> G�ran Thyni wrote:
> >
> > Bruce Momjian wrote:
> > >
> > > Would people tell me what platforms do NOT support the MAP_ANON flag to
> > > the mmap() system call?  You should find it in the mmap() manual page.
> > >
> > > *BSD has it, but I am not sure of the others.  I am researching cache
> > > size issues and the use of mmap vs. SYSV shared memory.
> >
> > SVR4 (at least older ones) does not support MMAP_ANON,
> > but the recommended in W. Richards Stevens'
> > "Advanced programming in the Unix environment" (aka the Bible part 2)
> > is to use /dev/zero.
> >
> > This should be configurable with autoconf:
> >
> > <PSEUDO CODE>
> >
> > if (exists MAP_ANON) use it; else use /dev/zero
> >
> > ------------
> >
> > flags = MAP_SHARED;
> > #ifdef HAS_MMAP_ANON
> > fd = -1;
> > flags |= MAP_ANON;
> > #else
> > fd = open('/dev/zero, O_RDWR);
> > #endif
> > area = mmap(0, size, PROT_READ|PROT_WRITE, flags, fd, 0);
> >
> > </PSEUDO CODE>
>
> Ouch, hate to say this but:
> I played around with this last night and
> I can't get either of the above technics to work with Linux 2.0.33
>
> I will try it with the upcoming 2.2,
> but for now, we can't loose shmem without loosing
> a large part of the users (including some developers).
> flags = MAP_SHARED;
>
> <PSEUDO CODE>
> #ifdef HAS_WORKING_MMAP
> #ifdef HAS_MMAP_ANON
> fd = -1;
> flags |= MAP_ANON;
> #else
> fd = open('/dev/zero, O_RDWR);
> #endif
> area = mmap(0, size, PROT_READ|PROT_WRITE, flags, fd, 0);
> #else
> id = shget(...);
> area = shmat(...);
> #endif
> </PSEUDO CODE>
>

What exactly did not work?

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