Re: mmap(MAP_PRIVATE) question

[Gianni Tedesco <giannit@securewave.com>]

On Wed, 2003-09-03 at 12:28, Jamie Lokier wrote:
> The page cache page is mapped into the application just like a shared
> mapping, until the application writes to the mapped region and
> triggers the copy-on-write fault.

that clears it up somewhat :)

> On the other hand you may not.  On some of the architectures which
> Linux supports, the CPU's cache is not sufficiently coherent to
> guarantee that what is written with write(), or by another process,
> will be seen in this application's memory.  Indeed, you might see a
> mixture of some of the written data and some of the data before it was
> written, with no particular guarantee of which bits of data or in what
> order.

Well, the thing I'm interested in is people overwriting parts of shared
libraries (at least those opened with dlopen). In my tests, I am using
mmap/msync to overwrite the library rodata section with
MS_SYNC|MS_INVALIDATE. When I do this the running copy (using
MAP_PRIVATE) appears unmodified, but no ETXTBSY error is given. What you
are saying would seem to indicate that the running program *should* be
modified.

Perhaps MS_INVALIDATE doesn't bother invalidating MAP_PRIVATE mappings?
Or am I missing a trick here? :)

(this is on intel btw).

-- 
Gianni Tedesco <giannit@securewave.com>