Re: [Qemu-devel] [PATCH v15 1/2] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap()

[Eduardo Habkost]

Hi,

On Fri, Apr 26, 2019 at 08:36:51AM +0800, Wei Yang wrote:
> From: Zhang Yi <address@hidden>
> 
> When a file supporting DAX is used as vNVDIMM backend, mmap it with
> MAP_SYNC flag in addition which can ensure file system metadata
> synced in each guest writes to the backend file, without other QEMU
> actions (e.g., periodic fsync() by QEMU).
> 
> Current, We have below different possible use cases:
> 
> 1. pmem=on is set, shared=on is set, MAP_SYNC supported:
>    a: backend is a dax supporting file.
>     - MAP_SYNC will active.
>    b: backend is not a dax supporting file.
>     - mmap will trigger a warning. then MAP_SYNC flag will be ignored
> 
> 2. The rest of cases:
>    - we will never pass the MAP_SYNC to mmap2
> 
> Signed-off-by: Haozhong Zhang <address@hidden>
> Signed-off-by: Zhang Yi <address@hidden>
> [ehabkost: Rebased patch to latest code on master]
> Signed-off-by: Eduardo Habkost <address@hidden>
> Signed-off-by: Wei Yang <address@hidden>
> Tested-by: Wei Yang <address@hidden>
> Reviewed-by: Stefan Hajnoczi <address@hidden>
> 
> ---
> v15: fix compile issue on pre-linux4.15
> v14: rebase on top of current upstream

Note that v14 was already merged, so the build fix would need to
be submitted separately.  However:

[...]
> +#ifdef CONFIG_LINUX
> +#include <linux/mman.h>
> +#endif /* CONFIG_LINUX */
> +
> +#ifndef MAP_SYNC
> +#define MAP_SYNC 0
> +#endif
> +#ifndef MAP_SHARED_VALIDATE
> +#define MAP_SHARED_VALIDATE 0
> +#endif

Why would we need this, if we added copies of mman.h to
linux-headers?

-- 
Eduardo