Re: patch for mmap MAP_ANON|MAP_SHARED

From: Christoph Rohland (hans-christoph.rohland@sap.com)
Date: Sat Apr 22 2000 - 10:31:12 EST


kanoj@google.engr.sgi.com (Kanoj Sarcar) writes:

> The patch looks good. I would just ask you to illustrate with a small
> program that mmaps /dev/zero MAP_SHARED and then does a "cat /proc/pid/maps"
> on itself. I think instead of reporting the root device numbers for the
> /dev/zero mapping, it will report the shmfs device numbers.
>
> Ie,
>
> instead of
>
> 08048000-0804e000 r-xp 00000000 08:01 XXXXXXXX /dev/zero
>
> it will say something like
>
> 08048000-0804e000 r-xp 00000000 AB:CD XXXXXXXX /dev/zero

Yes, that's right.

> I can't think of a problem this would cause, unless you claim an
> user might be confused to see /dev/zero, but a different device
> for the file.

I think this is reasonable since /dev/zero is a special device itself.

> Btw, even for MAP_ANON|MAP_SHARED, the filename reported via
> "cat /proc/pid/maps" will show up as /dev/zero (I _think_), did
> you want to change that?

No, the I think the current behaviour is fine since mmap /dev/zero and
mmmap MAP_ANON are semantically the same. So they can just show up the
same.

Greetings
                Christoph

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