Kanoj Sarcar wrote:
> > A program which opens /proc/pid/maps of some other process, and opens
> > the shared mapped file named in there, will open /dev/zero. And that's
> > broken: it doesn't show the correct data. For a MAP_PRIVATE mapping,
> > you get what you expect. But for a MAP_SHARED mapping, it should work
> > or the open should fail.
>
> For a MAP_PRIVATE mapping, if a process mmaps /dev/zero, changes a few
> pages, then another process comes in and opens /dev/zero, how does this
> second process see the changes made by the first?
I'm talking about opening a MAP_SHARED mapping, not a private one.
> > > And they have to show up as deleted since this memory object is only
> > > accesible to the process and its relatives. FD passing et.al. do not
> > > help for /dev/zero since mmaping the file again gives you a new
> > > mapping.
> >
> > ?? I was under the impression that the whole point of MAP_SHARED on
> > /dev/zero is that you can pass the fd around and multiple mappings
> > return the same pages.
>
> Nope. The whole point is cooperative inter process sharing. Being able to
> do what you suggest would be nice only if it is not too hard to implement.
So you can only use shared /dev/zero mappings to share across fork()?
Darn. And I thought it was an automagic equivalent to shm_open().
-- Jamie
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This archive was generated by hypermail 2b29 : Sun Apr 23 2000 - 21:00:21 EST