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SubjectRe: shmat problem
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Date
Alex Riesen <fork0@users.sf.net> writes:

> Doug McNaught, Mon, Jan 06, 2003 17:36:39 +0100:
> > > You have to add SHM_REMAP to shmat flags (see definitions of SHM_ flags).
> > Hmm, the manpage (on RH7.3 at least) doesn't mention SHM_REMAP. Nice
> > to know about it.
>
> RH7.3 manpage is quiet old, btw.

Apparently so.

> Linux manpages-1.54 (Dec 30 2002):
>
> The (Linux-specific) SHM_REMAP flag may be asserted in shmflg to indi-
> cate that the mapping of the segment should replace any existing map-
> ping in the range starting at shmaddr and continuing for the size of
> the segment. (Normally an EINVAL error would result if a mapping
> already exists in this address range.) In this case, shmaddr must not
> be NULL.

Wouldn't the OP's code still (potentially) have problems? What if you
had:

char my_shared_area[2048];
int my_unshared_var;

...

void *foo = shmat(id, &my_shared_area, SHM_REMAP);


Would my_unshared_var end up shared, since memory mappings have page
granularity?

-Doug
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