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SubjectRe: 64-bit shm: abi problems
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Linus Torvalds <torvalds@transmeta.com> writes:

> On Tue, 14 Dec 1999, David S. Miller wrote:
> >
> > Yes I see someone thought it would be a keen idea to
> > change shm_segsz to size_t from int. Why? I'm quite
> > happy with a 2G limit; you should have been using mmap
> > well before that anyway.
> >
> > mmap() still doesn't support anonymous SHARED+WRITE, which is why
> > people want sysv/ipv SHM.
>
> We really should try to fix the anon shared mmap issue, it should be
> possible these days reasonably easily (it's really mostly an issue of
> making sure that we can allocate "swapper_inode" inodes on the fly, with
> the one special swapper_inode remaining for regular paging).

But keep in mind that mmap SHARED+WRITE does not give you everything
(In fact it does not give you much at all, since you cannot unmap und
mmap the same region during a run).

I am just now working on shm code using struct files for shmat. This
would make shmat a special case of mmap. Also shm_open would be
trivial (and is in fact what I am heading for). shm_open gives you a
file descriptor to a shared memory object which you then can mmap.

My code is progressing now. I have most of the dentry/inode handling
ready and have now to debug the mmap case.

Greetings
Christoph

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