Re: don't let mmap allocate down to zero

[linux-os]

On Wed, 26 Jan 2005, Olivier Galibert wrote:

> On Wed, Jan 26, 2005 at 01:20:53PM -0500, linux-os wrote:
> > On Wed, 26 Jan 2005, Olivier Galibert wrote:
> > > Given that the man page itself says that unless you're using MAP_FIXED
> > > start is only a hint and you should use 0 if you don't care things can
> > > get real annoying real fast.  Imagine if you want to mmap a <4K file
> > > and mmap then returns 0, i.e. NULL, as the mapping address as you
> > > asked.  It's illegal from the point of view of susv3[1] and it's real
> > > annoying in a C/C++ program.
> >
> > mmap() can (will) return 0 if you use 0 as the hint and use MAP_FIXED
> > at 0. That's the reason why one does NOT check for NULL with mmap() but
> > for MAP_FAILED (which on this system is (void *)-1.
>
> All the paragraph was under an obvious "when you do not use MAP_FIXED"
> precondition.  The patch is not supposed to change anything to the
> MAP_FIXED case.  Malloc does not use MAP_FIXED.  Usual file mmaping
> as an alternative to read() does not use MAP_FIXED.
>
>  OG.

Okay. That's fine.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.10 on an i686 machine (5537.79 BogoMips).
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