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From: Dan Williams <dan.j.williams@intel.com>
Date: Tue, 22 Jan 2019 09:33:37 -0800
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Content-Type: text/plain; charset="UTF-8"
Subject: Re: [Qemu-devel] [PATCH V9 4/6] util/mmap-alloc: support MAP_SYNC
 in qemu_ram_mmap()
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>, Pankaj Gupta <pagupta@redhat.com>, Qemu Developers <qemu-devel@nongnu.org>, yu.c.zhang@linux.intel.com, Stefan Hajnoczi <stefanha@redhat.com>, Igor Mammedov <imammedo@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Xiao Guangrong <xiaoguangrong.eric@gmail.com>

On Mon, Jan 21, 2019 at 7:27 PM Michael S. Tsirkin <mst@redhat.com> wrote:
[..]
> > 2. The reset of cases:
> >       - we will never pass the MAP_SYNC to mmap2
>
> I don't see code probing for MAP_SYNC support. Did I miss it?
> But if all you want is to have old linux ignore MAP_SYNC,
> I think you got your wish automatically - just do not set
> MAP_SHARED_VALIDATE.

That will also cause new Linux to ignore MAP_SYNC.