Re: [Qemu-devel] [PATCH v14 1/2] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap()

[Stefan Hajnoczi]

On Wed, Apr 24, 2019 at 09:01:05AM +0800, Wei Yang wrote:
> On Tue, Apr 23, 2019 at 10:25:18AM +0100, Stefan Hajnoczi wrote:
> [...]
> >> +#ifdef CONFIG_LINUX
> >> +#include <linux/mman.h>
> >> +#else  /* !CONFIG_LINUX */
> >> +#define MAP_SYNC              0x0
> >> +#define MAP_SHARED_VALIDATE   0x0
> >> +#endif /* CONFIG_LINUX */
> >
> >MAP_SHARED_VALIDATE is is from 2017:
> >
> >  commit 1c9725974074a047f6080eecc62c50a8e840d050
> >  Author: Dan Williams <address@hidden>
> >  Date:   Wed Nov 1 16:36:30 2017 +0100
> >
> >    mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap 
> > flags
> >
> >This code fails to compile on Linux hosts with pre-4.15 headers.
> >
> 
> Ok, qemu build will fail on pre-4.15 linux.
> 
> >Instead you could use the following (even on Linux!):
> >
> >  #ifndef MAP_SYNC
> >  #define MAP_SYNC 0
> >  #endif
> >  #ifndef MAP_SHARED_VALIDATE
> >  #define MAP_SHARED_VALIDATE 0
> >  #endif
> >
> >Either way:
> 
> You mean replace the above code to:
> 
> #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

Yes, please.

This is not critical but I bet someone will hit this issue when
compiling a new QEMU on an old host.  This small tweak will save them
time.

Stefan

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