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

[Wei Yang]

On Tue, Apr 30, 2019 at 05:46:36PM -0300, Eduardo Habkost wrote:
>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:
>

Sure, I would spin a separate patch.

>[...]
>> +#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?

This is reported by Stefan.

https://www.mail-archive.com/address@hidden/msg612168.html

>
>-- 
>Eduardo

-- 
Wei Yang
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