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Date:	Tue, 11 Jan 2011 07:36:16 -0700
From:	Eric Blake <eblake AT redhat DOT com>
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Subject:	Re: Adding madvise function in cygwin with a #define
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On 01/11/2011 04:13 AM, jdzstz - gmail dot com wrote:
> Testing a linux application that uses "madvise", varnish cache, I have
> realized that in cygwin doesnot exists this function but exists the
> alternative "posix_madvise".
>=20
> Adding inside configure.ac script:
> +		AC_DEFINE([madvise], [posix_madvise], [In CYGWIN, madvise function
> is not defined, instead we use posix_madvise])
> +		AC_DEFINE([MADV_RANDOM], [POSIX_MADV_RANDOM], [In CYGWIN,
> MADV_RANDOM define is not defined, instead we use POSIX_MADV_RANDOM])

madvise is more powerful than posix_madvise; while this workaround may
have let you get varnish working, it is not a panacea for all clients of
madvise.  You are better off filing a bug report against varnish that
they should either use the POSIX interface, or add a configure-time
check for the presence of madvise.

> I think it could be interesting adding this defines to cygwin headers,
> at the end of <sys/mman.h> file
>=20
> #define madvise posix_madvise
> #define MADV_NORMAL POSIX_MADV_NORMAL
> #define MADV_SEQUENTIAL POSIX_MADV_SEQUENTIAL
> #define MADV_RANDOM POSIX_MADV_RANDOM
> #define MADV_WILLNEED POSIX_MADV_WILLNEED
> #define MADV_DONTNEED POSIX_MADV_DONTNEED

While these defines may make sense _once madvise is implemented_ in
cygwin, I don't want them any sooner.  In other words, we need a cygwin
port of madvise before we pollute the namespace with MADV_* constants.
That said, since Linux supports madvise and cygwin tries to emulate
Linux, a patch to implement madvise() is more than welcome.

--=20
Eric Blake   eblake AT redhat DOT com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org


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