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Re: [PATCH v2] [BZ #10283] localedef: align fixed maps to SHMLBA
- From: Roland McGrath <roland at hack dot frob dot com>
- To: "Carlos O'Donell" <carlos at redhat dot com>
- Cc: David Miller <davem at davemloft dot net>, vapier at gentoo dot org, libc-alpha at sourceware dot org
- Date: Tue, 28 May 2013 16:14:03 -0700 (PDT)
- Subject: Re: [PATCH v2] [BZ #10283] localedef: align fixed maps to SHMLBA
- References: <20130528194042 dot 1EF7B2C074 at topped-with-meat dot com> <20130528 dot 130721 dot 1721261559877509450 dot davem at davemloft dot net> <51A51186 dot 7070904 at redhat dot com> <20130528 dot 132601 dot 2200516495498570890 dot davem at davemloft dot net> <51A524FE dot 7040202 at redhat dot com>
> It's unfortunate that POSIX doesn't say more than just:
> "If MAP_FIXED is specified, the implementation may require that
> addr is a multiple of the page size."
>
> Perhaps we'll get Issue 8 to say something about SHMLBA in the
> non-normative RATIONALE section for mmap.
If the reality is as Dave says, that some implementations will simply
refuse MAP_FIXED attempts for page-aligned addresses that do not meet some
other constraints, then the normative standard needs to provide some way
for an application to find out how to meet those constraints. Otherwise
MAP_FIXED is essentially useless for anything other than overwriting an
existing mapping, and that means that the Linux implementations on some
machines are nonconforming.
Thanks,
Roland